Natural History of Vacant Lots [Reprint 2020 ed.] 9780520318441

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Natural History of Vacant Lots

California Natural History Guide No. 50

Natural History of Vacant Lots Matthew F. Vessel and Herbert H. Wong Drawings by Pamela Vesterby

UNIVERSITY OF CALIFORNIA PRESS Berkeley Los Angeles London

CALIFORNIA NATURAL HISTORY GUIDES Arthur C. Smith, General Editor Advisory Editorial Committee: Raymond Dasmann Mary Lee Jefferds Don MacNeill Robert Ornduff Robert C. Stebbins

University of California Press Berkeley and Los Angeles, California University of California Press, Ltd. London, England © 1987 by The Regents of the University of California

Library of Congress Cataloging in Publication Data Vessel, Matthew F. Natural history of vacant lots. (California natural history guides; SO) Bibliography: p. Includes index. 1. Vacant lot ecology. I. Wong, Herbert H. II. Title. III. Series. QH541.5.V27V47 1986 574.5'268 85-1073 ISBN 0-520-05250-1 ISBN 0-520-05390-7 (pbk.)

Printed in the United States of America 1 2 3 4 5 6 7 8 9

Editorial Note and Dedication We have reached a milestone in the publication of the California Natural History Guides. Natural History of Vacant Lots is Volume 50 in this continuing series devoted to the flora, fauna, physical features, and environment of California and the West. When this series was first proposed in the early 1950s, there were few publications available on California natural history other than technical works. Most of the popular books then available in California on natural history were written by Easterners about eastern species. I recall a book which supposedly covered the 100 most common native trees to be seen from coast to coast. The only native California species included was the Coast Redwood! A series of nature books used in California schools for many years was written and published in the Midwest. It treated primarily eastern species without mentioning that most of them did not occur in California. To find Cecropia moths the school children would need to travel east to Utah or north to Washington. To see Ruby-throated Hummingbirds they would have to go as far as Kansas, Oklahoma or Texas. Yet this editor, in 1926 as a fifth grader, was sent out by his teacher to find and collect Cecropia cocoons and to see and observe Ruby-throated Hummingbirds in the San Joaquin Valley. Forty years later, when my son reached the fifth grade in Hayward, he was given the identical assignment from the same books based on eastern plants and animals! This lack of reliable, pertinent publications on California natural history for the nonscientist was recognized in the late 1920s by San Jose State Professors Gayle Pickwell and Karl Hazeltine. Each completed his graduate work at Cornell University where a tradition of writing and publishing popular natural history had long existed. There they came under the influence of famed naturalists A. A. Allen, J. G. Needham, E. L. Palmer, A. H. Wright, and others. v

vi / Editorial Note and Dedication

In 1930 Gayle Pickwell and colleagues embarked on a program to provide information specifically on California natural history topics. Through 1935, under the series title Western Nature Study, they published books on birds, amphibians, wildflowers, trees, weather, and insects. These early natural history publications provided accurate and relevant California natural history information at a popular level for the first time. The first concerted effort to provide broad coverage of California natural history began in 1959 with publication of the first guides in this series. By mid-1985, total sales for the series passed the one-million-copy mark. Most titles remain in print today and projected plans include at least another 50 titles. Today we are joined by a multitude of publishers and individuals producing many excellent natural history books. There is no longer a dearth of good California natural history information available to the general public! I take great pleasure in joining authors Matt Vessel and Herb Wong in dedicating this fiftieth volume in the California Natural History Guide series to the memory of a group of dedicated naturalists and teachers who had a profound effect on the scope and development of field natural history in California— E. Laurence Palmer, Cornell University; and Gayle Pickwell, Karl Hazeltine, Carl D. Duncan, P. Victor Peterson, and Emily Smith of San Jose State College (now University). Arthur C. Smith, General Editor California Natural History Guides

Contents Introduction The Vacant Lot as an Ecosystem

ix 1

Seasonal Observations of Vacant Lots

13

Weedy Waysides and Roadways as Ecosystems

22

Some Characteristics of Weedy Plants

25

Suggested Activities

30

List of Common Species in Disturbed Areas

55

Descriptions of Plants and Animals Found in Vacant Lots and Waysides Plants Insects Amphibians Reptiles Birds Mammals

79 79 160 219 222 226 241

Glossary

251

Selected References

257

Index

261

Introduction A town or city is a disturbed natural area modified drastically by humans to accommodate their own needs. People have bulldozed, excavated, blacktopped, filled, and cemented large areas and built a wide assortment of buildings. To a large extent the city is an auto-environment—automobiles predominate. About two-thirds of a city is covered with streets, freeways, roofs, walkways, and parking areas. Most of the natural organisms that once flourished on the urban site have been pushed out by people. But wherever there are spots or edges of soil along waysides, buildings, and in vacant lots, a sturdy group of pioneer-type plants has claimed the growing space. The majority of these are foreign plant invaders that have the necessary adaptability to cope with adverse conditions such as pollution, trampling, lack of water, herbicide spraying, and cultivation. These specialized plants provide a variety of habitats for a miscellany of animals, primarily insects. Disregarded sites, usually vacant lots or other weedy areas, are found in or near urban sites throughout the country, and except for differences in climatic conditions, these sites have many similarities. Vacant lots may be construction sites or areas where a building has burned down or been demolished. Sites planned for public reconstruction often remain vacant for years. The number of vacant lots is surprisingly large in most communities. For instance, Berkeley, California, a city of about 120,000 people in 1979, has far more vacant lots than one would guess, despite the great influx of new residents. On the accompanying map (see Figure 1), the blackened areas indicate the vacant lot sites. A recent federal study found that on the average, 20 percent of the urban land in a community was underdeveloped or uncommitted and potentially available for use. This open space included surplus military property, abandoned lands, and dereix

FIG. 1 Vacant lots in a built-up city area—indicated by black rectangles. (Berkeley, California, 1977)

Introduction / xi

lict land adjacent to waterfronts, as well as unused streets, waysides, reservoirs, and even rooftops. Thus, vacant lots, waysides, and disturbed sites are within easy reach of most urban and suburban dwellers; this availability makes these sites excellent places to learn of the interrelationship of man with his environment and to gain an appreciation of ecosystems. Waysides and roadways are frequently neglected boulevards, driveways, building frontages, edges of cemeteries, playgrounds, and parking areas. Waysides and roadways are here considered only those areas in front of or adjacent to homes and other dwellings. (For an excellent description of roadsides in northern California, see Frenkel [1980].) Like vacant lots, these areas are ecosystems created and modified by people, with ecological characteristics similar to vacant lots. Some of these sites have trees and shrubs growing on them, but in most instances the areas are neglected. Disturbed areas are naturally colonized by weedy plants grown from seeds blown in by the wind and carried in by animals, especially man. These pioneer plants are fast growing, usually many seeded, widespread, and have adaptable growth habits. Although the plants growing in most vacant lots and waysides are often similar, each urban area may have some species that is unique to the area or more abundant in one area than in another. California, with its coastal areas as well as deserts, valleys, and mountain slopes, has plants adapted to each of these biotic zones. The most commonly encountered kinds of plants and animals are included in the checklist and species accounts of this book. In the headings and in the List of Common Species both common and scientific names are given. Elsewhere common names are frequently used alone. As in other California Natural History Guides, the common names for species are capitalized, but general names for a group of species or one or more genera are not capitalized. Thus filaree is not capitalized but White-stemmed Filaree is. The Index lists both common and scientific names.

xii / Introduction

Vacant lots are frequently an eyesore in the community. However, with a modest level of community group effort, more constructive use could be made of city vacant lots. These resource areas can serve as alternative recreation sites and ecological study areas and can be an enhancement to the community. It is hoped that the information in this book will enable the reader to recognize some of the plants and animals in weedy or disturbed sites around the neighborhood and to be intrigued and enlightened by the plant-animal interrelationships. Some selected investigations and activities are also suggested. We wish to acknowledge the suggestions of Gordon Edwards, James W. Tilden, and Sally Casey, San Jose State University; Arthur Nelson, San Francisco State University; Martin R. Britton, California State University, Sacramento; John Butler, California State University, Humboldt; Roger J. Lederer, California State University, Chico; Keith Woodwick and John Weiler, California State University, Fresno; Charlotte Clarke, Fullerton College; and Richard D. Vessel, Grossmont College, San Diego. Particularly, we wish to thank the series editor, Arthur C. Smith, for his valuable suggestions. The black and white drawings are by Pamela Vesterby with the exception of Fig. 9, which was prepared by Dorothy Thurman. We also wish to express our appreciation to Clarice C. Pickwell for the use of photographs by the late Gayle Pickwell, and to Lester A. Brubaker, Steve J. Grillos, Sandra Pieper, and Art Smith for their photographs. All photographs not credited are by the senior author. Many readers have long known and used plant family names such as Cruciferae, Leguminosae, Compositae, etc. Recent publications, including Munz, A Southern California Flora, use different names for some of the plant families. This natural history guide series normally follows Munz in the use of scientific botanical names, as we have in this book. However, so that readers not yet familiar with the new plant family names will not be confused, we have included the old familiar names in parentheses directly below the new names in the text headings.

THE VACANT LOT AS AN ECOSYSTEM

Even on casual observation, one can discover plants growing beside city buildings, along abandoned boulevards, by fences, in cracks of pavement, and, of course, in vacant lots. These plants—not planted or tended, ignored and mostly despised— are the "natural" vegetation of urban centers. These are hardy pioneer plants that strive to gain a foothold whenever there are suitable environmental conditions. Plants growing voluntarily in these disturbed sites are commonly called weeds. The term weed has varying definitions but usually refers to "pest" plants that compete with other, cultivated plants. A more appropriate term for plants that voluntarily colonize disturbed and waste areas is ruderal plants. This category includes both alien and native species found on these disturbed sites and does not have pejorative implications for the esthetic or economic worth of the plants. In a natural environment, there are no so-called weeds. Following each natural disturbance caused by fire, storm, or other catastrophe, a natural area is invaded by pioneer plants. These plants mature and die, building up leaf litter and thus changing soil conditions. The improved soil environment permits survival of other plants, and in time conditions change further. Still other plants invade the area, frequently replacing the pioneer plants, which can no longer tolerate the shade or crowded circumstances. This sequence of plant replacements is called ecological succession, and the process may continue until a relatively stable plant community is established on a natural 1

2 / Natural History of Vacant Lots

site. Such a mature or climax community never occurs in a vacant lot or wayside site because these sites are constantly disturbed. Yet the ruderal plants on these sites, although few in number of species and varying in the space they occupy, struggle with environmental problems similar to those of trees in a forest. The environmental factors of any habitat can be classified as abiotic and biotic in form. The abiotic or nonliving factors include soil, heat, light, and water, and in urban settings, polluted air is another important factor. Soil conditions vary with location and with modifications caused by bulldozing, filling, and dumping. Temperature and available light differ with seasons, as well as with location. Moisture is largely dependent on obtainable rainfall. An open area between tall buildings will sustain a community of plants and animals different from those in an open area on the outskirts of the city. The vast surfaces of roofs and roads absorb sufficient heat to raise the average air temperatures of cities two or three degrees. Polluted air, largely from vehicular exhausts whose pollutants are often further activated by sunlight, inhibits growth of some plants, as has been the case for the citrus trees, alfalfa, beans, and tomatoes, and orchids in southern California. Tiny particles of airborne pollutants can poison the soil and clog up the stomates (the microscopic openings in the leaves), which reduces the respiration and photosynthetic activities of the plant. This can stunt the growth of the plant or even lead to its death. In addition to sunlight, high humidity may intensify pollution damage; the low humidity levels of urban sites help prevent greater damage from various atmospheric pollutants. The biotic factors are represented by the living environment, the competition for growth with other plants, and the animals that may use the plant for food, shelter, or nesting. In the urban setting, man is invariably the dominant biotic factor. The nature of vacant lots varies according to location, season, and maturity. For instance, areas that are sprayed regularly, tilled, or cultivated will be different from those areas that are left alone. A disturbed area may result when a building is

The Vacant Lot as an Ecosystem / 3

burned or demolished. In such cases the remnant landscaping may endure for a time, if it can compete with the invading species that are not dependent on regular watering and care. Within the vacant lot and other disturbed environments, there is usually a number of distinct habitats. These may be pathways, areas adjacent to tended gardens (a kind of ecotone or transition zone), edges next to walks or pavement (the British call these verges), and cracks in paved areas, to mention a few. Pathways worn by much walking compact the soil particles and thereby reduce the air available to seeds and roots. As a consequence, there are few nitrifying bacteria found in this soil, and only plants with minimal nitrogen demands can grow successfully in these sites. Plants that establish themselves along pathways have several general characteristics. They are primarily annual plants, with small seeds. They are usually small in size or grow in a prostrate form; the stems are very flexible in order to withstand trampling. Although some species grow as rosettes, others may spread out, rooting along the nodes. Many have taproots, and the grasses all have fibrous roots. Studies of the plants found in trodden habitats have been made in many countries of the world. The species common in most of these regions as well as in California include: Annual Bluegrass (Poa annua), Perennial Ryegrass (Lolium perenne), Common Knotweed (Polygonum aviculare), Shepherd's Purse (Capsella bursa-pastoris), and Common Plantain (Plantago major). Others also frequently found include Pineapple Weed (Matricaria matricarioides), White Clover (Trifolium repens), and Common Dandelion (Taraxacum officinale). Additional plants commonly found along pathways of much of California are Prostrate Pigweed (Amaranthus blitoides) and Flax-leaved Fleabane (Conyza bonariensis). In the usual disturbed area, grasses often dominate the plant species, with members of the sunflower family usually second in abundance. In the environmental scheme of things, organisms live in

4 / Natural History of Vacant Lots

areas for which they are best suited. The place or area in which a plant or animal lives is called its habitat. Even a few scraggly plants will provide a habitat for some kinds of animals. The size of a habitat may be very small—a weed clump or the area under a rock, for example; or, if the organism roams or grows over the entire area, the habitat might be a field or pond. Usually, if two or more kinds of organisms occupy the same habitat, this is called a community. The organisms in the community perform different functions or play different roles. The plants called mallow and butterfly called West Coast Lady (Vanessa annabella) both occupy the vacant lot, and the plant serves as food for the insect. The earthworm and the mole both occupy the subterranean habitat, and the mole feeds on the earthworm. The function, or the part played by an organism in its community, is called its niche. Thus, in a vacant lot community there may be a variety of smaller habitats with different kinds of organisms; each has its particular niche or its particular function, which is usually as either a food producer or a consumer. In almost every habitat or community, green plants are the food producers. These organisms capture the sun's energy and use it to combine carbon dioxide from the air with water; this process is called photosynthesis and provides energy for plant growth, which results in plant foods—the energy source for all life. This fundamental energy-storing process and the liberation of oxygen enables life to exist on our earth. Green plants (photosynthetic organisms) are the producers in the ecosystem, and all other organisms are consumers. The consumers may also be categorized. Animals that feed primarily on plants are first-order consumers or herbivores. One can observe many kinds of herbivores in the vacant lot, such as snails, slugs, sowbugs, aphids, and caterpillars of numerous species. Some animals feed on both plants and animals and are known as omnivores. Other animals, like the ladybird beetle or the dragonfly, prey and feed on other animals; these are the carnivores—the second-order consumers. Third-order

The Vacant Lot as an Ecosystem / 5

consumers include the parasitoids—ichneumonid and braconid wasps and tachinid flies—which consume the tissues of their host plants and eventually kill them. Though not insects, the various spider species also found in vacant lots are effective predators, second-order consumers. These animals can capture organisms often larger than themselves with the help of webs. Some plant-insect associations are so close and interdependent that the insect and plant are almost never found apart. This is true for many aphid species; particular kinds of aphids are found on particular species of plants. A few of the betterknown plant-insect associations existing in vacant lot habitats include the Monarch Butterfly (Danaus plexippus) and milkweed; Green Dock Beetles (Gastroidea cyanea) and Curly Dock (Rumex crispus); Cabbage Butterfly (Artogeia rapae) and plants of the mustard family; and the Anise Swallowtail Butterfly (Papilio zelicaon) and Sweet Fennel (Foeniculum vulgare). Other animals feed on many plants. The House Finch (Carpodacus mexicanus), goldfinches, and towhees feed on seeds of many kinds. Mice and Cottontail Rabbits chew the greenery, but underground insect larvae and pocket gophers live on the root parts of plants. Moles may be found feeding on earthworms and insect larvae as well as plants. On or near the ground one is likely to find lizards, and possibly toads and salamanders, capturing stray insects and spiders. Mice and Black Rats (Rattus rattus) as well as Norway Rats (Rattus norvegicus) may be common in lots cluttered with rubbish. In larger, less urbanized areas, one may find garter snakes (Thamnophis spp.), Gopher Snakes (Pituophis melanoleucus), or Common King Snakes (Lampropeltis getulus), which seek amphibians, mice, gophers, and ground squirrels as food. The feeding relationships that link up what animal eats what, can be represented by a food chain. Grass (eaten by grasshoppers) represents a link of a food chain. (The arrow indicates that grass serves as food for grasshoppers, showing direction of energy flow from one organism to another.)

6 / Natural History of Vacant Lots

Food chains are seldom this short or simplistic because other animals usually get involved in the overall process. A likely combination would be: Ryegrass —* grasshopper —*• mouse —* Gopher Snake. Here the mouse and the snake are second- and third-level consumers. Further examination of the feeding relationships in a vacant lot reveals that food chains often overlap to form complex patterns, called food webs. Two possible vacant lot food webs are diagrammed in Figures 2 and 3. In the clutter of most vacant lots, the tires, boxes, boards, jars, and tin cans provide new habitats. Cans will usually collect rain water, making miniature pools for mosquitoes and other small aquatic life. Cardboard boxes and boards often invite termites, beetles, earwigs, sowbugs, slugs, centipedes, and the California Slender Salamander (Batrachoseps attenuates). And few fields exist without ants of several species busying themselves harvesting seeds, scavenging, or seeking any animal life they can overcome. House

Goldfinches

Mouse

I

Earwigs

Mockingbird

Garden Spiders

t

Tachinid Flies

Aphids

t

Painted Lady Caterpillar

Thistles FIG. 2

Syrphid Fly (Syrphidae)

House Fly (Musca domestica)

Crab Grass (Digitarla sanguinalis)

Crane Fly (Tipulidae)

imping Spider (Salticus sp.)

Green Bottle Fly (Phaenicia sericata)

Flesh Fly (Sarcophaga sp.)

Western Fence Lizard (Sceloporus occidentalis)

Green Bottle Fly

Dead robin Running or grass spider Funnel web spider (Agelenopsis naevia)

European Earwig {Forficula auricularia)

Measuring worm (G eometridae)

Silverfish (Lepisma saccharina)

Black Widow Spider (iatrociectus mactsns)

Click Beetle (Elateridae) Jerusalem Cricket (Stenopelmatus fuscus)

Hare Barley ( Hordeum leporinum )

Southern Alligator Lizard (Gerrhonotus mutticarinatus)

Field Cricket (Gryllus sp.)

Grasshopper (Acrididae)

Field Cricket

12 / Natural History of Vacant Lots

A change in seasons often means a change in the kinds of plants and animals. With the season's end, annual plants and many creatures complete their life cycle and die. On the ground the leaves make layers of leaf mold—a great habitat for springtails, ground beetles, sowbugs, and pill bugs, as well as millipedes and earthworms. These animals that eat dead organisms are classed as scavengers. Minute forms of animal life like the springtails and their relatives may become very abundant. Finally, microscopic fungi and bacteria get their energy by breaking down the unconsumed organic matter into the simple materials of which the plants were originally made. This, then, completes the complex web of life in the vacant lot. The producers are the green plants, making food from the gases in the air combined with water and minerals from the soil. Plants are eaten by the primary consumers, such as caterpillars, grasshoppers, mice, and rabbits. In turn, these animals are usually eaten by birds, toads, snakes, and cats—the predators or secondary consumers. Sometimes there are also third and fourth levels of consumers. Eventually, the individual organism dies. Now the scavengers consume it and finally the decomposers—bacteria and fungi—digest the remaining organismic matter to complete the task of recycling all of the once-living matter to organic compounds and then to simple gases and water. The goal of the living in this system is to obtain and store energy for growth and sustenance; when this no longer takes place, the organism is dead. This is the cycle of life that takes place in all ecosystems.

SEASONAL OBSERVATIONS OF VACANT LOTS

As an introduction to the study of a disturbed area or vacant lot, one might follow the changes that occur during the seasons. Unlike the northeastern and midwestern parts of the country, California does not have obvious seasonal changes, except in the mountainous areas. In general, a Mediterranean type of climate prevails, with long hot dry summers and then the winter rains. Thus, the apparent spring season occurs early, with the first rains, and it also terminates early. The following is a summary of observations made of several vacant lots in the city of San Jose. The rationale for this area's selection was simply that San Jose is characteristic of cismontane California, which represents a good part of the state, except for the deserts and high mountains. Four seasons or periods were identified for this area. The first period occurred in the late fall, just after the first soaking rains. It might be called the germinating period. The second period was the time of maximum cold and wetness, occurring usually during January and February. A third period coincided with the calendar spring, when vegetative growth and animal reproduction were in full swing. And the final period occurred in mid- to late summer when weedy plants dominated the landscapes of disturbed and waste areas. The Germination Period

The first soaking rains, coming in late fall, initiate the greening of California landscapes. The vacant lots and waste areas, usu13

14 / Natural History of Vacant Lots

ally dry and sometimes dusty, take on a new fresh look, as grasses and perennial and broad-leaved weeds germinate. A few warm, sunny days hasten the growth of seedlings. Hundreds of seedlings spring up where the plants of last season dropped their fruiting stalks. Conspicuous plants in addition to grasses include mallows, filarees, Common Groundsel, Petty Spurge, Annual Bluegrass, Common Sow Thistle, and Common Dandelion. In other areas, there might be Common Chickweed, Milk Thistle, docks, mustards, and Prickly Lettuce. Thick-rooted perennial plants that have been cut off by cultivation may renew their growth, and in a short time some will form beautiful symmetrical rosettes of leaves. These radial designs are common in mallow, filaree, Curly Dock, and Common Dandelion. As with plants, the animal inhabitants of vacant lots are also affected by the cool fall temperatures. Most insects have completed their life cycle for the season and now either become food for scavengers or part of the debris. Some insects survive, crawl into cracks and holes in the ground, and begin a variable period of inactivity. The field crickets, Jerusalem Cricket, and several species of ground beetles withdraw to these habitats. During the brief warm spells, they may emerge, but as it cools they again retreat to their sanctuaries. Butterflies like the Mourning Cloak, West Coast Lady, Buckeye, and Cabbage Butterfly hide for protection. House, tachinid, and blow flies; Honey Bees; and ladybird beetles, like butterflies, make an occasional venture out of concealment during warm periods. The first soaking rains of fall also appear to signal the emergence of the damp wood and subterranean termites. These insects are the special long-winged reproductive forms that usually make a brief flight before dropping to the ground in search of mates. On the ground, they break off their wings and pair off in follow-the-leader fashion. Then they scurry about to find a site to start a new colony. The site could be a cardboard box, a board, or an exposed piece of wood. They burrow in and in the darkness start a new colony.

Seasonal Observations / 15

On the few standing stalks of mustard or Prickly Lettuce, one might find the orb webs of several species of garden spiders. These spiders are mostly females with bulbous abdomens filled with eggs and silken fluid. The males are usually less than one-fourth the size of the females and difficult to find. At the end of the fall season, the female orb weavers spin their egg sacs, deposit the eggs, and seal them over. Their energy sapped by this arduous effort, the spiders waste away and drop to the ground, unless they are picked off by some bird or other predator. Slime trails in the foliage or on the ground indicate the presence of snails and slugs. Being nocturnal, these creatures mostly confine their activity to the twilight and night hours. With moisture available everywhere, the slimy clan can move about with ease to select their favorite plant foods. Earwigs also belong to the nocturnal group, and if the temperatures are high enough, these insects will venture out to feed on plants and occasionally on aphids. To many Californians, the fall season is usually announced by the plaintive calls of the Golden-crowned Sparrow and its associate, the White-crowned Sparrow. These large sparrows commonly forage in small groups of about four to eight on the ground or in the low shrubbery and tall weeds. Lesser Goldfinches are often seen perching on the weed stalks especially of Prickly Lettuce and Common Sow Thistle and feeding on the seeds. Occasional flocks of Brewer's Blackbirds, American Robins, House Sparrows, and Starlings may search the ground for seeds and insects. The Cool Rainy Season The winter rains pack down the fallen leaves and litter and soak the soil. Now the bacteria can better utilize their digestive enzymes and gradually decompose the organic matter to essentials—carbon dioxide, water, nitrates, and other compounds. Molds and other fungi will permeate the leaf litter, and here and there toadstools or mushrooms may pop up. The Fairy-ring is a commonly found mushroom that also occurs in lawns. In

16 / Natural History of Vacant Lots

boulevard areas and roadways, the Oak-root Fungus may grow in masses on infected trees. Low temperatures and occasional freezes may kill off many of the aphids, white flies, and other exposed insects, but a Careful search of the vegetation should turn up some of the survivors. Conspicuous in many lots and roadways may be the stout, naked, tan-colored stalks of Tree of Heaven sprouts with their large leaf scars. On the mature trees there may be clusters of dried fruits or samaras, which flutter off with each gust of wind. Tree of Heaven is one of the few trees that can be categorized as a weedy species. It is a common shrub alongside buildings and waysides, and seedlings are often found in rain troughs, gutters, and in cracks of pavement. Here and there a branch of dried mustard stalk may show signs of life as a few yellow blossoms pop open. The brown dried stalks of Curly Dock show a growing collar of broad green leaves at their base. Coyote Brush, a native shrub, is in full bloom, and the female plants are quite showy with their mass of white blossoms, which also have a distinctive odor. The seedlings of Milk Thistle, Bristly Ox Tongue, Common Groundsel, Wayside Peppergrass, and Shepherd's Purse may be found. Piled up against fences and other obstructions are tumble weeds, White Amaranth, and Russian Thistle, along with segments of Prickly Lettuce, mustards, and species of goosefoot. Other plants such as Common Dandelion, clovers, oxalis, Common Sow Thistle, Panicled Willowherb, and Goose Grass are fairly common along sidewalks and roadways. Animals living in this same habitat include sowbugs, pill bugs, millipedes, centipedes, snails and slugs, and occasionally darkling ground beetles and earwigs. Earthworms are usually near the surface or just under the leaf mold. Hidden in the mustard greenery is the greenish Cabbage Butterfly caterpillar and the Checkered White Butterfly, and sometimes just below ground level, live several species of cutworms. Where leaves have piled up, ladybird beetles are often found, apparently hibernating, for they become active when warmed up. Some species

Seasonal Observations / 17

migrate and overwinter in mountain areas. On tree trunks and fences, a search may reveal the hairy cocoons of the woolly bear caterpillars or tiger moths and the chrysalids of the Anise and Tiger Swallowtail butterflies, both overwintering in the pupal stage. In small communities and city edges, vacant lots may harbor moles and gophers cultivating the ground; mounds of soil indicate their presence. Moles forage for earthworms, although they also eat plant parts; gophers feed on plant parts, especially the fleshy roots. Evidence of cats and dogs may also show up. As early as January, hummingbirds begin their nesting activity. Spring Season By the time calendar spring, March 20, arrives, the herbaceous plants in the valleys and foothills of California are almost full grown and some beginning to flower. During most years, this is a period of dwindling rainfall, and by mid-year most annual plants have reached maturity. Untended urban lots are usually lush with vegetation. Warm weather germinators like Pineapple Weed and plantain must find open spaces to sprout, and so they are usually found in pathways, edges, and waysides. The perennial Orchard Morning Glory has sprouted many shoots, and the small leaved Yellow Oxalis and Petty Spurge crowd the open areas near the lot edges. Competition for light is critical. Fast growing forms may shade some plants to the degree that they are unable to grow. For one interested in sampling the natural foods close at hand, this is the best season to harvest. The new leaves of Curly Dock, mustards, pigweeds, and Lamb's Quarters can all serve as potherbs. In some instances, it may be necessary to discard the first two boilings of water because the leaves of most species get bitter as they grow older. Young Miner's Lettuce can be used like lettuce. Common Dandelion leaves, especially those that are blanched because they have been partially covered by a rock or other debris, can be used like lettuce and

18 / Natural History of Vacant Lots

are especially good when sprinkled with hot bacon chips or drippings. Areas with moist soil may be carpeted with Common Chickweed or Miner's Lettuce. Common Chickweed grows so rapidly that it seems to take over an area in just a few weeks. The conspicuous grass species include the bromes, wild oats, rye, and foxtails. There are also areas overgrown by young plants of filarees, Bur Clover, mallows, mustards, and Milk Thistle. Very green spots in the lots will often be caused by fertilization from dog dung. In some areas, the nitrogen content may be so high from dung deposits that only Common Groundsel and Pineapple Weed can survive. Visible animals include Monarch, Mourning Cloak, swallowtail, West Coast Lady, American Painted Lady, Buckeye, Chalcedon Checkerspot, Mylitta Crescent, and Cabbage Butterflies. These roam over the area in search of nectar or host plants on which they can lay their eggs. Honey Bees, House Flies, bluebottle flies, bee flies, and wasps visit plants to seek food or to find other insects that they can parasitize. An examination of the mustards or Prickly Lettuce stalks will usually show some young shoots covered with sapsucking aphids or scale insects. And nearby there should be larvae of the lacewing fly or the ladybird beetle—common predators. If a weed is pulled up and shaken, a greenish caterpillar of one of the white butterflies may drop out of the foliage. Just beneath the soil may be cutworms, earthworms, wireworms, and sodworms, as well as field crickets, the Camel Cricket, and the rarer, large-headed Jerusalem Cricket. In addition to these, there is a good chance of encountering earwigs, centipedes, millipedes, ground beetles of several species, as well as slugs and snails. In early spring, individuals or small groups of ladybird beetles may be disturbed in hibernation. The seemingly awkward meandering daddy-long-legs contrasts sharply with the rapidly moving wolf spider crawling about the ground. Any pile of leaves or plant debris will probably harbor an abundance of springtails, pill bugs, and sowbugs. Western Fence Lizards or alligator lizards may be found in

Seasonal Observations / 19

some areas, depending on the number of cats roaming the site. Alligator lizards will frequent the shade—dense grass and under boards—whereas Western Fence Lizards seem to prefer the sun—the more open, cleared areas. Birds frequenting the lots may include the winter resident White-crowned and Golden-crowned Sparrows, as well as Dark-eyed Juncos, Brown Towhees, House Finches, and goldfinches. The few mammals in these areas, other than domestic cats and dogs, include mice, Broad-footed Moles, and in some areas, pocket gophers as well as Black Rats. This is often the season when man enters the scene and disturbs the habitats of vacant lots. The "shabby" appearance of the areas, as well as the fire hazard, prompts him to control the vegetation by mowing, spraying, or cultivation. As a result of this action, the area may be brought back to its pioneer stage of succession. Again, the fast growing annual plants take over as soon as the seeds can germinate and the perennials survive by sending up new shoots. T h e Late Summer Season By the first of July, most of the native wild flowers have completed their life cycles as have the annual grasses. Many of the weedy plant species have a prolonged or a later flowering period, so these plants are quite conspicuous during late summer. The tall, bushy Wild Radish and mustards show mostly podlike fruits, but a few may still have shoots of green. Curly Dock displays its dense clusters of brownish fruits, and is often collected for dry flower arrangements. Scraggly stalks of mallow, with their cheese-like fruits, show withering or discoloring of leaves that are often speckled with rust. Many of the weedy members of the sunflower family such as Prickly Lettuce may still be in bloom, as may Telegraph Weed, Coyote Brush, and Flax-leaved Fleabane, with their masses of dirty, cottony fruiting heads. Salsify (Tragopogon porrifolius), with its beautiful golf ball size, tan colored fruiting heads—an enlarged version

20 / Natural History of Vacant Lots

of the Common Dandelion fruiting head—is a striking sight. Near the outskirts of cities where farm crops have been grown or in alkaline waste areas such as exist near the San Francisco Bay Area salt marshes, the Wild Beet may live in vacant lots and waysides. These plants somewhat resemble Curly Dock but are more scraggly, and the fruits are spaced more widely on the stems. Where undisturbed, Russian Thistles reach maturity and form a two- or three-foot tumbleweed ball, which will eventually break off at the ground and then roll along with the wind, all the while disseminating seeds. Most of the grasses have seeded and dropped their grains or have had them carried off by animals, leaving behind the pale yellow stalks; especially conspicuous are Annual Ryegrass and Wild Oat. The upright stalks of Sweet Fennel, like small umbrella skeletons, are often found with a few green shoots still surviving. Close examination of this greenery might reveal the last feeding larvae of the Anise Swallowtail butterfly. In some areas the silky seeds of the Narrow-leaved Milkweed pop out of pods. Here, too, on the remaining greenery, there may be Monarch Butterfly caterpillars, yellowish Milkweed Aphids, and Large Milkweed Bugs. The meter-or-more-tall Milk Thistle is tan dry now and is identified by the spiny involucred heads and spiny dry stalks. Along the edges and in cracks of walks, Prostrate Pigweed will be in bloom, although the flowering is inconspicuous. Shear off the top and the buds below will send up new shoots, which quickly flower and seed. The fleshy purslane flourishes where moisture is adequate. Areas that have been bulldozed or shallowly disced to control weeds are often covered with Orchard Morning Glory, Bermuda Grass, or some other perennial that survived the cultivation. Narrow-leaved Milkweed is frequently one of the survivors, and the stout sprouting twigs of Tree of Heaven may also be conspicuous. Late summer and fall is also the time for observing spiders. The tall stalks of mustard, Sweet Fennel, and Prickly Lettuce provide the framework over which scores of orb weaving spiders spin their webs. The abundance of spiders, mostly Banded and

Seasonal Observations / 21

Golden Garden Spiders, will naturally vary with the food available. Near fruit canneries that attract millions of vinegar flies, a dense population of spiders can be expected. Insects at this time of year include grasshoppers, flies, and occasional butterflies feeding on the greenery or blossoms available, as well as a variety of ground dwellers—the darkling ground beetles, earwigs, and field crickets. At dusk and through the night, the crickets call. Ants may trail along, carrying food to their nests. An aggressive search may be necessary to locate snails, slugs, sowbugs, and earthworms, for the habitat is now usually quite dry. On sunny days, look for the Western Fence Lizard; it may be stalking the smaller invertebrates. Finches may frequent the flower stalks, plucking out the seeds, and family flocks of House Sparrows and Starlings may visit the sites to find food. Broad-footed Moles and pocket gophers are usually deeper underground, and the pocket gopher often eats off the deeper roots of mustards and Prickly Lettuce. On occasion a shrew will show up, too. Cats and dogs have selected sites and paths in the vacant lots, where they wander about and leave their various signs. All seems to be awaiting the first soaking rains.

WEEDY WAYSIDES AND ROADWAYS AS ECOSYSTEMS

Waysides of sidewalks, driveways, untended roadways, and edges of parking areas are also urban ecosystems. The plants here are few in kind, and the ones likely to be found are Annual Bluegrass, Flax-leaved Fleabane, Low Amaranth, and Common Knotweed. At the edges of parking lots, the common weedy tree, Tree of Heaven (Ailanthus altissima) may establish itself. Occasionally cotoneaster, privet, pyracantha, and Coyote Brush (Baccharis pilularis) will be found. Some plants that adjust to a low-ground profile are Narrow-leaved Plantain, mallows, Bermuda Grass, and the ubiquitous Common Dandelion. Roadways with perhaps somewhat better soil may sprout Pineapple Weed, filarees, Prickly Lettuce (Lactuca serriola), Common Sow Thistle (Sortchus oleraceus), Annual Ryegrass (Lolium multiflorum), brome grasses, foxtail grasses, Miner's Lettuce (Claytonia perfoliata), Common Chickweed (Stellaria media), Common Groundsel (Senecio vulgaris), the star thistles, and the Italian Thistle (Carduus pycnocephalus). Wayside areas and lots contain "escapees" and survivors from previous home gardens, if such plants can subsist on the scanty water supply and the lack of care. Some of the common forms include: Elms (Ulmus spp.), Acacia (Acacia spp.), English Ivy (Hedera helix), Sweet Alyssum (Labularia maritima), Butterfly-bush or Summer Lilac (Buddlia davidii), Himalaya Berry (Rubus procerus), Tree Mallow (Lavatera arborea), Cretan Lavatera (L. cretica), Malva Rose (L. assurgentiflora), Red Valerian (Centranthus ruber), Black 22

Waysides and Roadways as Ecosystems / 23

Locust (Robinia pseudo-acacia), and peas (Lathyrus latiflorius and L. odoratus). These plants' straggle for life and their energy relationships with other organisms illustrate the character of this ecosystem. The abiotic factors—water, wind, soil, and so on—limit the sustained growth of plants in waysides and roadways, but as a biotic factor, humans remain the principal change agent. Attempts to control weedy plants by mowing, cultivating, or spraying often initiate the beginning of a new cycle of growth. As soon as conditions are suitable, the plants sprout and start growing again. Perennial plants send up new shoots once the spray has worn off. Thus, in suitable warm areas, some plants appear to have no seasonal cycle but instead germinate or sprout, grow to maturity, seed, die, and start the process again, irrespective of the time of the year. Animal species, finding a haven on or among plants, include aphids, bees, wasps, and butterflies. One handsome butterfly is the Buckeye (Junonia coenia), whose larvae live on plantains. Another commonly found plant-insect association is the West Coast Lady butterfly feeding on mallow. The life cycle of this butterfly can be easily observed when it is brought indoors. Upright plants harbor crab spiders and jumping spiders that pounce on their insect prey, and stretched among the vegetation, the orb weaving spiders spin webs to catch flying or other small insects. A casual search will often locate ants tending aphids and mealybugs on plants. Nocturnal animals, such as earwigs, field crickets, ground beetles, earthworms, sowbugs and pill bugs, snails and slugs may be found at the base of shrubbery or in the pockets of leaves. At edges of parking areas in the soft fine soil, the little pits of ant lions, also called doodle bugs, can sometimes be seen. At the bottom of each pit a ferocious appearing larva patiently awaits unwary ants or other small prey crawling about. And if a piece of wood or cardboard lies on the ground for a time during the fall and winter seasons, one will probably find termites living underneath, feeding on the cellulose. Ants and termites appear to be enemies, so a habitat will usually accommodate one or the other, but not both.

24 / Natural History of Vacant Lots

Other animals that visit the waysides and roadways are birds, mice, squirrels, and sometimes rabbits. Birds include House Sparrows (Passer domesticus), House Finches (Carpodocus mexicanus), White-crowned and Golden-crowned Sparrows (Zonotrichia leucophrys and Z. atricapilla), Brown Towhees (Pipilo fuscus), Lesser Goldfinches (Carduelis psaltria), Brewer's Blackbirds (Euphagus cyanocephalus), Starlings (,Sturnus vulgaris), pigeons, and occasionally American Robins (Turdus migratorius). Most of these birds feed on seeds, fruits, insects, earthworms, or food scraps. The edges of large parking lots and airport runways provide a refuge for mice and rabbits that live in and feed on the vegetation. On the overhanging wires and utility posts, especially on the edge of the city or town, one may see a Loggerhead Shrike (Lanius ludovicianus) or a Kestrel or Sparrow Hawk (Falco sparverius) and in some areas Burrowing Owls (Athene cunicularia) search on the ground for large grasshoppers, lizards, small birds, or mice. Both Fox Squirrels (Sciurus niger) and Black Rats often use the powerlines as runways. In roadway communities, one can with little effort identify the producers and the consumers and determine how they relate to one another.

SOME CHARACTERISTICS OF WEEDY PLANTS

People often think of weeds as plants out of place—plants that interfere with the activities of people. A number of features enable weeds to be successful. Dominance of Alien Plants The majority and most aggressive of weeds are alien plants. In their native surroundings, they do not appear aggressive, for over the many generations of growth, they have acquired a variety of pests and diseases that attack them and keep them in check. Introduced to a new suitable habitat without their accompanying controls, these plants often multiply quickly and create problems. For example, in 1788 a prickly pear cactus (Opuntia sp.) was introduced into Australia for use as a sheltering hedge around ranch houses and as a possible fodder plant. By 1910 ten million acres were infested with the plant. A search was made for the natural enemies of the cactus, and the most successful parasite was found to be a brown moth (Cactoblastis cactorum) from Argentina and Uruguay. These insects were collected and reared in laboratories and then set free among the cacti. The nocturnal moths lay their eggs on the plants, and the eggs hatch into larvae that tunnel into the stems and roots of the cacti. Pathogenic organisms then complete the disintegration. Now the cactus is under control in Australia, and a large enough resident population of moths prevents a recurrence of explosive growth. In California the European leaf beetle (Chrysolina quadrigemina) was introduced to control a plant on range lands 25

26 / Natural History of Vacant Lots

called St. John's Wort (Hypericum perforatum). It is commonly called Klamath Weed, because the worst infestation occurred along the Klamath River. By 1940 about 250,000 acres of range land became hazardous to grazing animals because of the growth of this weed. The beetles were introduced in 1945-46, and by 1948 they had established themselves. Within a few years the weed had been largely destroyed, and the beetles now appear to keep Klamath Weed under control. These are examples of biological control that have been used for controlling other species of plants as well as animals. A spectacular success story was the extensive colonization of rabbits in Australia and New Zealand and the eventual control of these rabbits by the introduction of a virus disease called myxomatosis. California succeeded in controlling Cottonycushion Scale on oranges by importing an Australian ladybird beetle called the Vedalia Beetle. Thus, alien organisms without their natural controls have an advantage over local organisms, and this probably is a major factor in the success of alien plants and animals in adapting to a new environment. Some of these are escaped cultivated plants such as Chicory (Cichorium intybus), Horehound (Marrubiuf vulgare), Poison Hemlock (Conium maculatum), and Salsify (Tragopogon porrifolius). Some escaped ornamental plants are English Daisy (Bellis perennis), Scotch Broom (Cytisus scoparius), and Red Valerian. Methods of Distribution

Among other means of transport, people can act as agents for seed distribution. Further means include: Impurities in Seed Some common weed seeds are often mixed with purchased seeds: Shepherd's Purse, Common Chickweed, Sweet Fennel, Common Groundsel (Senecio vulgaris), Annual Bluegrass, Narrow-leaved Plantain (Plantago lanceolata), and Sheep Sorrel (Rumex acetosella). Ballast from Boats and Sweepings from Freight Cars Seeds thus transported include: Petty Spurge (Euphorbia peplus),

Some Characteristics of Weedy Plants / 27

Red-stemmed Filaree (Erodium cicutarium), Black Mustard (Brassica nigra), and Bird's Foot Trefoil (Lotus corniculatus). Packing Materials Hay and straw have been used widely for packing pottery, china, and machinery. The packing usually contains some weed seeds; the seeds of chickweed and several species of brome grasses have often been found in these packing materials. Wind One of the most widespread means of weed seed dispersal is wind. The plumed seeds and fruits of the sunflower and milkweed plant families and some of the grasses are carried for long distances by wind currents. The airborne fruits of the Common Dandelion are well known. Plants such as the tumbleweeds Russian Thistle (Salsoli kali) and White Pigweed (Amaranthus albus) break off at the soil level when mature, and the entire plant is rolled by the wind across fields, dropping seeds as it goes. Water Early cities were all established on or near the shores of oceans, lakes, and rivers, since water was the chief means of transportation. Rainwater and surface run-off often can carry seeds into streams, where the buoyant seeds or fruits float along to be deposited later in fields. Some sedges, ragweed, dock, cocklebur, and mustards are adapted for dispersal by water. In California, irrigation ditches act as principal routes for water-borne seeds. Animals Many weedy fruits and seeds are sticky or have hook-like spiny appendages that attach to the fur of animals or to clothing. Cocklebur, Horehound, some docks, Goose Grass (Galium aparine), and plantain seeds can attach. Seeds become sticky when wet and then may be carried on the feet as well as in the fur and feathers of animals. Harvester ants, which collect and store seeds, are also important distributors of seeds. In addition to seed hitchhikers, many weed seeds and fruits are spread by being eaten and then passed through the ani-

28 / Natural History of Vacant Lots

mal's digestive tract. A few of the many species spread this way include: Scarlet Pimpernel (Anagallis arvensis), Shepherd's Purse, Narrow-leaved Plantain, Common Knotweed, Wild Radish, Indian Chickweed, and Common Dandelion. An interesting observation was made in England that some seeds had better germination rates after they had passed through an animal's digestive tract. Seeds of the Narrow-leaved Plantain, for example, had a 100 percent germination rate after passing through the digestive system of a dove, compared to the only 56 percent germinated without this treatment. Explosive mechanisms Plants like impatiens, some oxalis, and Wisteria have explosive fruits. The common Yellow Oxalis (Oxalis corniculata) found in lawns, gardens, and vacant lots has a cylindrical pod, and if touched when ripe, the entire pod will suddenly split and scatter seeds up to two or three feet. Those who have lived near a Wisteria plant are probably familiar with the explosive energy of these seeds. The force may propel the seeds thirty feet or more. Other Advantageous Features Another advantage many weeds have over many native plants is the great number of seeds each plant may produce. A few examples are: Tumble Mustard (Sisymbrium altissimum)— 511,200 seeds; Horseweed (Conyza canadensis)—243,000

Some Characteristics of Weedy Plants / 29

seeds; Prickly Lettuce (Lactuca serriola)—52,700 seeds; and Common Purslane (Portulaca oleracea)—193,200 seeds. In addition to the production of enormous numbers of seeds, many weed seeds have a long dormancy period, that is, they can remain viable underground for years. Seeds of Rough Pigweed (Amaranthus retroflexus), Purslane, Lamb's Quarters (Chenopodium album), and Black Mustard have germinated after being buried for twenty to forty years. Jimson Weed {Datura stramonium) and Yellow Bristlegrass (Setaria lutescens) have survived twenty years of burial, and Chickweed, Narrowleaved Plantain, and Tumble Mustard have likewise germinated after being buried for ten years. Another advantage weeds have is the ability to self-pollinate and self-fertilize. This acts as a guarantee of seed production. Plants with this ability include Shepherd's Purse, Chickweed, Wild Radish, and Tumble Mustard. Some species, such as Common Dandelion and Bristly Ox Tongue, are even more unusual. In the ovaries of these plants, the seeds may be formed without any fertilization. This process is called apomixis, and in a sense might be considered a kind of natural cloning. In many ways weedy plants are well equipped for survival in disturbed urban areas as well as in cultivated fields and gardens.

SUGGESTED ACTIVITIES

Introduction

There are many fascinating investigations anyone can carry out that will lead to a keener awareness of the interrelationships in vacant lots and similar wayside or roadside ecosystems and to some fundamental ecological knowledge, values, and conduct. Basically, there are four ecological principles that characterize living forms in the environment: diversity, interdependence, adaptation, and change. Diversity concerns the variations in living as well as nonliving forms of the ecosystem. For living forms, one can observe variations between species as well as variations within species. Diversity in nonliving forms is apparent as changes in light, water, and soil types. Interdependence refers to the interrelated effects that organisms and their environments have on each other. Adaptation concerns variations in organisms that can make them more enduring and persistent in surviving the variety of hazardous conditions found in vacant lots and roadside habitats. Change is one of the more obvious phenomena on disturbed sites, and it is the most "constant" or persistent of all features of such ecosystems. With changes in season come changes in growth and kinds of plants. Animal behavior changes over the year. Humans create changes by littering, by cultivating, by treating the sites with herbicidal or insecticidal sprays, and by physically altering these sites. (Children and dogs and cats are primarily responsible for such alteration.) 30

Suggested Activities / 31

The actual organisms one finds in a disturbed area will largely depend on the geographical location. Coastal urban areas are usually more moist than inland ones; mountain slopes and desert regions have physical limitations of extreme cold or heat, short seasons, drought, and variable winds. In addition to geographically related environmental conditions, the vacant lot ecosystem is affected by the characteristics of the urban or suburban environment. These include the changes in atmospheric heat, moisture, and chemical composition owing to the effects of many square miles of roofs and roadways, the presence of industrial plants, the combined metabolism of thousands of human beings, and the toxic gases emitted by numerous automobiles and factories. The urban environmental conditions of principal California cities are, for the most part, quite similar, and the conspicuous organisms found around these areas are often identical. There are intriguing problems particular to the species of organisms in these disturbed communities, especially regarding these species' struggle for survival. These characteristics present an opportunity for investigation and suggest the following questions: 1. What are the techniques for identifying and studying various organisms? 2. What are the ecological interrelationships of these organisms with their environment and how can they be determined? 3. What are the life histories—the stages of repopulation and succession—of organisms in a newly disturbed site? 4. How do the various organisms adapt and survive in this kind of ecosystem? 5. What are the limiting factors controlling some of the common species? 6. What biotic and habitat associations can be identified? 7. What are some of the food-energy relationships? 8. What natural plant foods exist in these environments and how can they be identified?

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9. What is the human impact on these ecosystems, and what, if any, regulations exist to prevent vacant lots from becoming dumping sites for rubbish or that prescribe the liability of individuals using vacant lots for observation? 10. What are the implications for reevaluating and developing environmental literacy, attitudes, values, and ethics? 11. What are the successive changes in the ecosystem that result from the change of seasons? These questions form the basis of the suggested activities that follow. This listing of activities is not intended to include all possible activities, but rather to present a few ideas that can act as a springboard to others. Identification, Census, and Animal Signs

One of the first steps in exploring the ecosystem of a vacant lot is to determine what lives there—the plants and animals such as insects, birds, reptiles and mammals. This can be done by recording the types of species and the number of organisms and by looking for signs of the organisms, as the following activities demonstrate. Identifying Plants One way of identifying and studying plants is to collect seedlings or young plants. Use mediumsized vegetable cans from which both ends have been removed. Place this tin cylinder over the plant and press down with your foot until the top of the can is level with the ground. Then wiggle the container with its specimen and soil out of the ground. These specimens can be placed in a tray of wet sand or sawdust and kept growing until they bloom. Identification can then be made with certainty. Determining Plant Distribution One can also determine the relative abundance and distribution of species, that is, how much of the area is covered by grasses, Orchard Morning Glory, mustards, and so on. One method of doing this—the line intercept transect method—is to use a 50-foot length of

Suggested Activities / 33

heavy string or cord. At 6-inch intervals, make marks with a marker pen on the length of cord. Stretch the cord from one edge of the lot to the other and peg it down at each end. Select at random at least five locations to stretch the line across the lot. There will thus be 500 places (100 marks per cord X 5 cord locations) to make observations and recordings. Begin making observations at the first 6-inch mark on the first location; at this point count all the kinds and numbers of individual plants (not the number of leaves) that can be touched with the blunt end of a pencil. For example, suppose that from the 500 possible observation points, 200 were found to have grasses (rye grass), 50 bare soil (no plants), 100 Orchard Morning Glory, 100 mustard, and 50 miscellaneous plants. One could then conclude that the lot was 40 percent grass, 20 percent Orchard Morning Glory, 20 percent mustard, 10 percent miscellaneous plants, and 10 percent bare soil. (This is a good project for a group activity, as it permits two pairs of observers to work from each end of the 50-foot line—one observing, one recording.) Making a Census of What Is Living and Growing in the Vacant Lot Making a census of the organisms is a good way to begin study of a disturbed area. Make a grid map of the area to pinpoint the locations of plants and animals. Then, record the types, numbers, and location of plants found. Because making an inventory of plants is a key activity in the study of an ecological area, much of this book is devoted to brief descriptions and sketches designed to assist in the identification of the more common plants of disturbed areas. Making a census of animals is not as direct as making a census of plants. Look for evidence of animal activity and animal residents; the next activity describes how to do this. Finding Signs of Visiting Organisms In a search for signs of animals, consider the following clues: pawprints; chewed leaves, blossoms, or fruits; burrows in leaves or stems or in the ground or fence posts; parasites on caterpillars, or aphids or other insects; droppings of birds, rats, mice, rabbits, and dogs;

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empty bottles and cans, paper tissue, paper or plastic cartons—garbage; nests, feathers, shed skins, fragments of birds' eggs; and snail or slug trails. Although some of these animals may be residents, some will just be visiting or passing through the area. This further complicates taking a census of certain animal forms. A great variety of animal activities are described in Common Native Animals, by Vessel and Harrington (see the Selected References below). How Many Kinds of Insects on a Lot? One of the classical stories about the numbers of species of insects found in an urban lot is the account by Dr. Frank E. Lutz, former Curator of Insects at the American Museum of Natural History. Dr. Lutz wanted more museum space and more staff for the entomological section and propositioned the museum director as follows: "If the museum will agree to raise my salary by $10 a year for every species above 500 that I honestly find on our lot [his 75 X 200 foot yard in suburban New York City], I shall agree to have my salary reduced $10 for every species short of 500." Although the director did not agree to the arrangement or believe that 500 species of insects could be found, Dr. Lutz proceeded to make a count. He actually collected a total of 1,402 species! Determine the number of species of insects in a study area of your choice. As Dr. Lutz discovered, there are a lot of insects in an urban lot. Life Histories

Tracing the life history of a common organism provides a good opportunity for understanding how the four ecological concepts identified in the introduction to this chapter are interwoven. Observing the Life Histories of Insects The very common Cabbage Butterfly can be observed in its various stages throughout the year and in many areas. Watch the adult butterfly behavior. Where does it land? What is it doing on the plants? Look for eggs under leaves of mustard plants, Wild Radish, and other plants. Consider what advantages there are to laying

Suggested Activities / 35

eggs on the undersides of leaves. Examine the eggs with a hand lens and note their shape, color, and pattern. When the eggs hatch, observe the change in life-style and behavior of the caterpillar. Describe how its appearance equips this animal for survival. What kind of food does it eat? Devise a way to determine how much a caterpillar eats. How far does it travel in a day? Simple containers to observe insects can be made of plastic or plastic screening. Boxes with magnifying glass on the top are also available for closer observation. What changes take place as the caterpillar grows? How many molts occur? What happens to the molted skin? Describe the chrysalid stage and record the period of time spent in this pupal stage. Finally, what is the appearance of the emerging adult?

rapae)

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FIG. 8 Life Cycle of a Monarch Butterfly (Danaus plexippus)

Recording Observations Here is one record of observations on Monarch Butterfly development. Oct. 4 Oct. 9

Oct. 20

Nine eggs collected on different plants of Narrowleaved Milkweed. All but one egg hatched; three caterpillars observed while emerging from egg; after a tenminute rest, caterpillars ate their egg shells. Six caterpillars remain. Molting occurred as follows: "Face mask" broke off, and the skin was

Suggested Activities / 37

worked backward until it slipped off posterior end; after caterpillar dried off, it turned around and ate its skin. By counting the facial masks it was possible to determine how often the caterpillar molted. First-hatched caterpillar preparing to pupate. Oct. 29 All six caterpillars pupated, four at the following times: Oct. 22—12:10 PM; Oct. 25—3:45 PM; Oct. 27—8:40 AM; and 9:08 AM. Nov. 7 First butterfly emerged at 1:10 PM (female). Nov. 13 Second butterfly emerged about 1:30 PM (male). Nov. 14 Third and fourth butterflies emerged about 5:00 PM.

Nov. 16 All butterflies have emerged. This familiar life cycle is just one example of the numerous developmental life histories and interrelationships that occur in the ecosystems of vacant lots and waysides. Keeping Live Insects Insects can be kept alive for observation in many kinds of containers (Figure 9a-d). One of the simplest is the shoe or cereal box, with window cutouts covered with plastic. The plastic may be stapled to the box or attached with a plastic adhesive, rubber cement, or adhesive tape. If the insect is feeding, the greenery can be kept fresh by using a small paper milk carton filled with water. A container

a

b

c

d

FIG. 9 a, Shoe-box cage for rearing insects, b, Terrarium made from gallon jar. c, Insect cage: two cake pans and a screen-wire cylinder, d, Test chamber made from two jars and lids.

38 / Natural History of Vacant Lots

half filled with moist sand will also keep the plant food fresh. Insects, especially caterpillars, will fall into open dishes containing water and drown. Gallon jars with wide mouths are satisfactory terraria for maintaining live insect cultures for study. If they are modified as shown in Figure 9-b by attaching to the cover a square piece of plywood that has the same width as the diameter of the bottle, the bottles will not roll around. There are many other simple ways to keep insects. An excellent cage is made of wire or plastic screening and two cake or pie tins (Figure 9-c). The authors have used this type of cage successfully for rearing and studying insects for a number of years. A simple test chamber for studying small animals can be made from two canning or mayonnaise jars. Remove the metal covers. Cut through both covers in the form of an X (Figure 9-d) and flatten two opposite flaps inside one cover and the other two flaps inside the other cover. This will keep the covers joined and also allow an opening. Two jars may be held together by screwing them into these covers. (A "miracle" glue may be used to attach covers instead of cutting.) Observing the Life Histories of Larger Animals Animals— small mammals and birds—are somewhat more difficult to observe, since they are more elusive in their habitat and do not do well when confined. However, the dedicated observer can learn something from animal life histories. For instance, many birds return to the same nesting area year after year—such as the Mockingbirds, chickadees, and Starlings. Birds are a natural choice for observation and are a good example of the effect of seasonal changes on life history. Binoculars and a field guide are a great help in identifying birds. Peterson's Field Guide to Western Birds is recommended. The authors have written an elementary book called Introducing Western Birds in which the illustrations are stylized emphasizing only the key identifying features. Try to identify several species and observe their behavior (singing, nest building, mating, feeding). Return the next sea-

Suggested Activities / 39

son and determine which species are still around. Many birds sing in spring and in California some begin with the first rains in December. During mid-summer after nesting the birds are molting and cease their singing. Noting when singing occurs can help identify changes in yearly behavior. In the vacant lot one must know if he is seeing the same individual time after time so varied marking systems are used. Sometimes the feather patterns or the peculiarity of the song can identify individual birds. Marking reptiles is accomplished in several ways. Turtles and tortoises are marked by filing small notches on either side of the upper shell or carapace. In snakes a V-shaped notch is cut along the posterior margin of the ventral (belly) scales just in front of the anal opening. Mammals are more difficult to mark and there is also danger of being bitten. If one is really serious about studying mammals, experts from fish and game departments or local colleges and universities should be consulted. Ecological Interrelationships

Ecological interrelationships reflect the ecological principle of interdependence defined in the introductory section of this chapter. Some examples of interdependence include: the water, mineral, and soil requirements necessary for plant growth; the effects of nitrifying bacteria in root nodules of legumes and other plants on plant growth; the modification of carbon monoxide and utilization of carbon dioxide by green plants in photosynthesis; and the modification of urban weather owing to transpiration by plants. The following activities can help the observer understand the interrelationship and interdependence of the organisms and their environment—the vacant lot ecosystem. Comparing Other Species' Effects on Seed Germination The success of weeds is due largely to their ability to grow rapidly and produce seeds under what appear to be adverse conditions. If an area is examined just after the first soaking rain, thousands of seedlings will be found. Sometimes it appears

40 / Natural History of Vacant Lots

that an entire vacant lot is populated by one kind of plant only. This has been seen in fields composed entirely of London Rocket or Field Mustard, although most often the species are mixed. It is known that some seeds when germinating give off a chemical that inhibits the growth of other species. Moreover, the roots of some plants actually poison their and other future seedlings. An investigator at the University of Illinois reported that a first-year disturbed field may contain a dense stand of ragweed (Ambrosia sp.) over three feet tall. The plants of the next generation are stunted, usually not much more than six inches tall, and by the end of the third year, few ragweed plants remain. This was also noted in fields of Eastern Horseweed in North Carolina and also in California with the mustard called London Rocket. This raises interesting problems regarding control of these plants, particularly if they are the cause of hayfever. To study the effects of seed germination inhibitors, collect soil from under Eucalyptus, California Pepper, or California Laurel trees (suspected to be germination inhibitors). Plant seeds in these soil samples and in samples of soil taken from a vacant lot, a garden, or from soil collected beneath oak and redwood trees. (If sterilized soil is desired, it can be prepared by heating soil in an oven at 300 degrees for about one hour.) Compare and record rates of seed germination in each soil sample. Adaptation As noted in the introduction to this chapter, organisms develop or have adaptive characteristics that enable .them to survive in ecological settings such as vacant lots. Examples of adaptive forms of behavior are: the abundance of wind-dispersed seeds; the animals' assumption of a prostrate form during certain threatening conditions, such as mowing or trampling; the production of small leaves and seeds that will withstand being trodden on; the development of a tolerance to particular poisons; and the possession by some organisms of a disagreeable taste or odor or of characteristics that make them hazardous to touch.

Suggested Activities / 41

Evaluating How Plants Adapt to Disturbed Areas In considering plants' adaptations for invading and surviving in disturbed areas, it is necessary to examine these plants' requirements for germination, how these plants tolerate the usually difficult conditions of growth and competition, and how they manage to propagate themselves vegetatively as well as by producing seeds. The following activities illustrate some of these adaptations. Dispersal of Seeds To establish themselves as pioneer plants in a barren area, seeds must be introduced. The dispersal of seeds by wind is a common way that plants populate this type of ecosystem. Such seeds are those of dandelions, thistles, and many other plants of the sunflower family, as well as some grasses like Ripgut Brome, Wild Oat, and Hare Barley. Other seeds may hitchhike on the fur of cats and dogs, and some are dispersed by birds. The seeds of many fruits eaten by birds will pass through the bird's gut undamaged and are thus able to start new plants if dropped in proper sites. Areas under birds' roosting locations will often show evidence of this, and undoubtedly the wide distribution of Poison Oak can be attributed largely to birds that feed on the berries of this plant. As an exercise, collect samples of seeds that are airborne, that "hitchhike," or that are carried by birds. Regenerative Plant Parts How do plants adjust to discing, spraying, or fire? It is obvious that vacant lots and waysides are generally not optimal growing areas. Therefore, plants existing there must have features that enable them to survive. Some perennial plants regenerate their leaves if they are cut off. Remove the top leaves of a growing Dandelion or Narrowleaved Plantain and observe the plant for a few weeks. Note and study the regrowth of a Dandelion or Curly Dock root. Orchard Morning Glory has an extensive root and underground stem system. Dig up a plant and trace the underground system. How small a piece of root or underground stem can develop into a new plant in the field? Investigate similar adaptations of some thistles and Bermuda Grass.

42 / Natural History of Vacant Lots

Leaf Arrangement Other plants exhibit other adaptations for survival. Some grow in the form of rosettes, hugging the ground. What other plants have the leaf arrangement of a Common Dandelion? Is filaree, Curly Dock, or Narrow-leaved Plantain in the area? How have these plants adapted to survive mowing and trampling? High Seed Production and Longevity Compare the number of seeds in a mustard plant with those of a sunflower or other cultivated plant. Most weeds produce enormous numbers of seeds and ensure the chances of survival of the species. Purslane and some pigweeds may have more than 190,000 seeds on one plant; Prickly Lettuce, 50,000; and Flax-leaved Fleabane, more than 240,000 seeds. The seeds of some weeds are also long lived. The U.S. Department of Agriculture and the Michigan Experiment Station found that weed seeds that were buried for forty years would still germinate. This is an adaptation seen in several mustards, pigweeds, purslanes, ragweeds, Common Chickweed, and Narrow-leaved Plantain, to name a few. Rapid Growth and Maturity Some plants show very rapid growth. Grow some seeds of Annual Blue Grass, Common Sow Thistle, or Common Chickweed and compare their rate of growth with the rate of growth of flower seeds like Nasturtium or Zinnia. How might rapid growth be advantageous to a plant? Comparing Adaptations of Vacant Lot Plants Plant growth is affected by soil, rainfall, and variations in light. In general, plants that grow in the sun are smaller with shorter internodes and smaller leaves than are plants in trampled areas, such as pathways. In cooler soils plants tend to spread out and become prostrate; in higher altitudes and along the coast plant blossoms often appear larger and brighter in color. Compare the adaptations of some weedy plants such as Cheeseweed, Common Knotweed, and Bermuda Grass. Find specimens growing in cracks of driveways and parking lots, on worn pathways, and under trees or shrubbery of vacant lots.

Suggested Activities / 43

Which of these plants display the generalized survival features listed above and in what ways? Devise a way to determine the interrelationship between the amount of light and the growth of seedlings. This can be done in your home or a classroom. What other growth factors can be tested? Keeping a Notebook on Plant Adaptations Select a number of common weedy plants and describe some of the adaptations that support their survival. Record an inventory of the habitats and the different adaptations in a field notebook. Supplement with sketches and leave space to add research information. Limiting Factors Each species can tolerate a limited range of light intensity, temperature, moisture, mineral concentration, or crowding in its environment. When any one of these conditions exceeds the limits of tolerance the organism (if a plant) will die or (if an animal) will move out. Careful observations will reveal that plants appear limited as to where they grow and when they grow. Investigating Limiting Factors on Plant Growth Examine a well-trodden pathway through a vacant lot and locate the distribution of plants from the center of the path to its edges. Make five site observations of the plants found at distances 10, 20, 30,40, and 50 cm. from the center of the path. After listing the plants, enter them in a chart like the one shown below. Trampling or Wear Extreme Heavy Medium Light 10cm

20cm

30cm

40cm

Distance from center of path

50cm

44 / Natural History of Vacant Lots

Look for such plants as the following: Annual Bluegrass, Perennial Ryegrass, Hare Barley, Common Knotweed, Sheep Sorrel, pigweeds, Bur Clover, mustards, mallows, pineapple weeds (Matricaria spp.), Common Sow Thistle, filarees, and Tree of Heaven. What do you suspect are the factors that limit plants to these specific regions? Other investigations could be designed to compare plants found (1) in areas of sunlight or of shade, (2) in very moist or very dry areas, (3) under conditions in which the color of light or the pH or soil acidity to which plants are exposed varies, and (4) in areas treated with various amounts and kinds of fertilizers. Identifying Limiting Factors for Insects Insects are the most common animals associated with plants, particularly in disturbed areas. Since the plants in such areas have developed in accordance with the limitations of the disturbed environment (by growing closer to the ground, less densely, or smaller), this also affects the species and numbers of insects to be found there. Study the types of insects in the vacant lot and record their numbers. In the process of collecting insects for identification and study, observe and record the plant species on which the insects are found. Many insects are found only on specific plants, and this dependent relationship provides identification clues. Likewise, the behavior of insects on or in plants is a helpful clue. Often it may be necessary to collect the plant or plant parts with which the insect is associated. Immature insects are not easy to identify; therefore, collecting the plant enables the observer to note the life cycle of the insect. (It should be noted that it is difficult to identify most moths and butterflies except in the adult stage.) Food Webs and Predator-Prey Relationship Food webs or food chains and predator-prey relationships characterize every ecosystem, and the vacant lot or disturbed area

Suggested Activities / 45

is no exception. These food webs are intricate and delicately balanced; the loss of.one member of the chain, through spraying of insecticides or other externally introduced control methods, creates an imbalance in the entire web. The disturbed environment provides an excellent opportunity for observing this ecological mechanism as well as for understanding the structure of predator-prey relationships. Locating Invertebrates in Food Webs A variety of invertebrates other than insects inhabit these disturbed environments and interact in the food webs; snails are a good example. Collect and bring indoors several snails and confine them in a box for a period of four or five days. How do they adapt to this drying condition? Identify the snails with a numeral, a letter or some other cue, using small self-sticking labels or a bit of fingernail polish. Release them from some central spot in the vacant lot and observe their movement and behavior. Collect data on distances traveled, time consumed, hiding places, and so on. Record evidence of behavioral adaptations and structural adaptations. On your vacant lot map or census grid, where would snails be found during a hot dry spell? How do snails fit into the food webs of a vacant lot? Finding Out What Eats What An illustration of a predatorprey relationship is the ladybird beetle and aphids. Examine the new shoots of mustard and other plants for colonies of aphids. In company with aphids, there are often both the adult and immature stages of the ladybird beetle as well as ants. Observe the interaction between ants and aphids. What would you call this relationship? Here is a clue: Aphids are often called "ant cows." Also, observe the ladybird beetle and its larvae interacting with the aphids. Look for other examples of predators that prey on aphids—particularly the lacewings, some small wasps, and occasionally earwigs. Differentiating an Insect Predator from a Plant or Nectar Eater Insect predators are faster, more aggressive, and have different mouth parts than nonpredator insects. Compare the

Gaffer Snake ( Thamnopbis sirtalis) •Si

Bermuda Grass (Gynodon dactylon)

^

California Slender Salamander ( Batrachoseps attenuates)

Pillbugs ( Armadillidium vulgare) Gray Slug (Deroceras reticulatum)

Sowbugs

California Toad (Bufo bóreasL

European Brown Snail (Helix aspersa)

Snaileater (Scaphinotus sp.) Darkling Ground Beetle (Tenebrionidae)

:eous ground beetle (Carabidae)

50 / Natural History of Vacant Lots

mouth parts of a caterpillar, a butterfly, a grasshopper, and a ladybird beetle. Use a hand lens to examine the mouth parts up close. Exploring the Predator-Prey Relationship Search for organisms at night with a flashlight. Try covering the light with red cellophane if they seem to be disturbed by white light. Survey the ground area for animals and evidence of animal activity. Figure 11 illustrates some animals found at night and their probable feeding relationships. Studying the Effects of Control Methods Record the species and numbers of insects in a vacant lot, following the steps outlined in previous activities. Find out when the lot will be mowed, tilled or sprayed for weed, insect, or other animal control. After several months, make another census and note any changes of species or decreases in the plant and animal populations. Natural Plant Foods Before organized farming and gardening were established, plant foods were collected wherever they grew. Cultivated plants are all derived from wild plants, which have been developed and modified through breeding and selection. Pigweeds (Amaranthus spp.) were extensively used by the American Indians, and even today in parts of Mexico and Central America, these plants are grown for food and planted between rows of corn. Amaranthus species are found through much of the world and have been recommended as an alternative to our common grains where there is a threat of famine. Many weedy plants are considered by herbalists to have healing properties. This is an intriguing field to explore, and in recent years there has been a resurgence of interest in the use of herbs, especially herbal teas. Associated with the herbs are numerous poisonous plants, which, of course, the investigator must learn to recognize.

Suggested Activities / 51

Collecting Food Plants Collect and prepare some vacant lot plants that are safe for a meal. Many weedy plants are excellent foods if picked at the proper time and properly prepared. Obviously, the safe and nontoxic species must be identified and distinguished from unsafe plants. Edible and Useful Plants of California, by Charlotte Clarke, and Early Use of California Plants, by Edward K. Balls, offer detailed instructions on the preparation and cooking of many weedy species. Many plants can be used as salad greens, for spices, or boiled or steamed. Be especially careful of mushrooms, as many species can be deadly. Mushrooms of Western North America, by Robert and Dorothy Orr, will help with the identification of these nongreen plants, and Poisonous Plants of California, by Thomas C. Fuller and Elizabeth McClintock, is a general survey. (All of these books are California Natural History Guides.)

Human Impact and Environmental Ethics

Vacant lots are largely the results of human activity, and human beings continue to act as the most influential agent of change in these ecosystems. Left alone, a disturbed area operates as a natural ecosystem. However, numerous ecosystem interactions are affected when humans intervene by spraying herbicides or insecticides, by trampling, by physically altering the area, or by depositing garbage and waste products. Such intervention can abruptly alter the availability and types of small habitats; this will in turn affect animal as well as plant diversity and population dynamics. Checking on Human Impact Using the census grid shown earlier, check for evidence of human disturbances and keep a record of the changes that occur. What impact do these intrusions have on the support systems of the organisms? What is the nature of these impacts? How successful are organisms in adapting to the changes? Record your observations in a cumulative record.

52 / Natural History of Vacant Lots

If there are no major disturbances in the study environment, then as an investigatory exercise, intentionally remove or introduce materials into this environment and observe the consequent changes. How may the results of such an investigation change ecological awareness and how should we react to this behavior? What are the implications for developing a general awareness and sensitivity to ecological attitudes, values, and ethics? Examining the Rubbish in a Vacant Lot The amount of litter in vacant lots reveals social attitudes about the environment; for the most part (in spite of the recent emphasis on environmental issues), people discard waste locally, nationally, and globally without thought or consideration of the effects these waste products will have, in particular, on the ecosystem of a vacant lot, and, in general, on the global ecosystem. What can be done to change these perceptions and behavioral styles? Devise and describe plans or programs to develop

FIG. 12 Berlese Funnel with Light

Suggested Activities / 53

appropriate environmental awareness and ethics, using the vacant lot as a microcosm for change. Make up a general list of litter materials found in vacant lots and group the materials according to how quickly or slowly they will deteriorate or decompose. Devise a scheme to test the biodegradability of the most common litter materials. What organisms are found living among litter? How does the litter affect the organisms living here? Describe a litter habitat and how organisms have adapted to living here. Finding Small Organisms in Leaf Litter The simplest way of getting small organisms out of leaf litter is to use a Berlese funnel (Fig. 12). This is a large funnel with a piece of screen or hardware cloth in the middle of it and a container of alcohol below the spout. Litter is placed on the screen and an electric light bulb is placed above the funnel. As the litter dries out, the animals move downward in the funnel and eventually fall into the container. This is a good device for determining the kinds and population sizes of small spiders, insects, and other arthropods in soil debris. Checking the Impact of Cats and Dogs Cats are the main predators in most vacant lots, for they are often free to roam the neighborhood, while dogs may be kept in a yard or on a chain; some dogs are allowed to roam at night. These animals explore and hunt in these vacant lots and both cats and dogs frequently use these areas to deposit their dung. The acid nitrogenous fertilizer thus deposited has a decided effect on the plants and small organisms living there. A number of fly and beetle species live and breed in animal dung and hasten its decomposition. This is an interesting investigation in itself. Examine a site in your neighborhood for this animal behavior. Compare the plants growing in the dung area with those on the rest of the vacant lot. Identify some invertebrates that seem to be associated with these highly nitrogenous sites.

54 / Natural History of Vacant Lots

A Year-Long Concept of Studying Ecosystems Year-long observations of seasonal changes are useful in studying the vacant lot ecosystem. Refer to page 13 for an account of the progression of changes occurring in a vacant lot during a calendar year. Vacant lots or waysides that are cultivated annually provide excellent opportunities to see the colonization of a barren area by pioneer-type plants. Studying Seasoned Changes Clear off an area of ground. Use a hula hoop or some kind of a frame that defines a small space and can serve as a measuring and counting aid. Divide the hoop into four quadrants by tying two strings as diameters at right angles to each other. The quadrants will demonstrate the variations that can occur in small areas. Remember to place the hoop in exactly the same position on the ground each time weekly observations are made. The location can be marked with stakes to ensure accuracy. On a piece of paper, plot the weekly changes in each quadrant. Note species and population differences from quadrant to quadrant each time. Changes in size or shape of plants and evidence of attack by insects can be recorded. Did the plants germinate evenly over the area? Compare the annuals with the perennials. Where did the seeds for these plants come from? How many species of plants did you find? When did the first evidence of animals appear? Did the soil texture change as the plants grew? Similar year-long activities can be designed to study the seasonal effects on insects or birds. The developmental stages of insects and the mating, nesting, and migration patterns of birds have direct seasonal relationships. (See the record of Monarch Butterfly development and the description of birds' life histories in the previous section concerning life histories.)

LIST OF COMMON SPECIES IN DISTURBED AREAS

This is a general listing of some plants and animals commonly found in disturbed urban sites in California. The broad categories suggested are arbitrary, but urbanization tends to generalize the kinds of species found. Foothill communities are defined as up to the Yellow Pine belt, about 3,500 feet in elevation; mountain communities are above 3,500 feet.

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