Patches and Structural Components for a Author(s): Richard T. T. Forman and Michel Godron Source: BioScience, Vol. 31, No. 10 (Nov., 1981), pp. 733-740 Published by: American Institute of Biological Sciences Stable URL: http://www.jstor.org/stable/1308780 Accessed: 02/04/2009 21:20

Your use of the JSTOR archive indicates your acceptance of JSTOR's Terms and Conditions of Use, available at http://www.jstor.org/page/info/about/policies/terms.jsp. JSTOR's Terms and Conditions of Use provides, in part, that unless you have obtained prior permission, you may not download an entire issue of a journal or multiple copies of articles, and you may use content in the JSTOR archive only for your personal, non-commercial use.

Please contact the publisher regarding any further use of this work. Publisher contact information may be obtained at http://www.jstor.org/action/showPublisher?publisherCode=aibs.

Each copy of any part of a JSTOR transmission must contain the same copyright notice that appears on the screen or printed page of such transmission.

JSTOR is a not-for-profit organization founded in 1995 to build trusted digital archives for scholarship. We work with the scholarly to preserve their work and the materials they rely upon, and to build a common research platform that promotes the discovery and use of these resources. For more information about JSTOR, please contact [email protected].

American Institute of Biological Sciences is collaborating with JSTOR to digitize, preserve and extend access to BioScience.

http://www.jstor.org Patches and Structural Components For A LandscapeEcology

Richard T. T. Forman and Michel Godron

Landscapesas ecologicalunits with structureand functionare composed primarily Between the stands of a cluster are of patchesin a matrix.Patches differ fundamentally in originand dynamics,while transitionzones or , which may size, shape,and spatialconfiguration are also important.Line corridors, strip corri- vary from being abrupt to gradual and stream and dors, corridors,networks, habitationsare major integrative structural wide. In less disturbedlandscapes, grad- characteristicsof 29 .(Accepted for publication May1981) ual community gradients may be com- mon or uncommon,depending upon how Landscapessurround us, yet curiously tion among stands of the cluster. If one sharp environmental changes are with it is hard to find people with the same moved several kilometers away within distance. However, with greater distur- concept of a landscape. Artists and hu- the landscape, one would find a similar bance, especially by human activity, a manistscommonly portray the landscape cluster of stands with similar interac- landscape mosaic of patches as what the eye can perceive and some- tions. Moving on, one would find this with distinct boundaries comes into times limit the idea to naturallandforms cluster repeateduntil enteringa different sharperfocus. or .Such a landscapegener- geomorphologicalarea, or an area sub- We suggest that landscape' is a dis- ally includes a high degree of spatial jected to differentnatural or human dis- tinct, measurableunit with several inter- heterogeneity.In geographicalliterature, turbances. Here, a different cluster of esting ecological characteristics. Within the landscape plays a central role, with interacting stands would be evident as the landscape is a recognizable and re- most definitionsfocusing on the dynamic one entered, for example, a landscapeof peated cluster of and distur- relationship between two characteris- ridges and valleys, a suburban land- bance regimes. The boundary between tics-natural landformsor physiographic scape, or a sandy forested landscape. landscapes (which differ in geomorphol- regions and human cultural groups Such observationsare at the heart of the ogy and ) is relatively dis- (Grossman 1977, Mikesell 1968, Sauer landscapeconcept, which we describeas tinct, particularly in vegetation struc- 1963). In this article we ask whether the follows. ture. Ecologically, landscapestructure is landscape is a recognizable and useful A landscape is a kilometers-widearea measured by the distributionof energy, unit in ecology, with a distinctive struc- where a cluster of interacting stands or mineralnutrients and species in relation ture and function that can be analyzed, ecosystems is repeated in similar form. to the numbers, kinds, and configura- as is done for organismsor ecosystems. The landscape is formed by two mecha- tions of the component ecosystems. What are the structuralcomponents of a nisms operating together within its Landscape dynamics is the flux of ener- landscape and their characteristics?Are boundary-specific geomorphological gy, mineralnutrients, and species among there interesting,indeed critical, ecologi- processes and specific disturbances of the component ecosystems, and conse- cal questions facing us that may be the component stands. quent changes in those systems. solved using a landscape approach? Landscapesvary considerablyin areal The key landscape structurequestions Walkingin a small area of an agricul- extent, and a localized area of a few today center on the importanceof num- tural landscape, one might encounter a metersor hundredsof meters across is at bers, kinds, and configurationsof eco- corn field, a bean field, an abandonedold a finer level of scale than a landscape. systems. Randomness is rare within a field, an uplandoak stand, and a lowland Because of the area's geomorphology, landscape. The overwhelmingnumber of elm-ash-sycamore woods adjacent to the complex of landforms and parent one another.If one studiedthis cluster of materials present is relatively constant 'Relatedconcepts: A region is bounded by a com- five specific communitiesor stands, one over a landscape. Each stand has a char- plex of physiographic,economic, social and cultural characteristics(Dickinson 1970, Isard 1975). A stand would find fluxes of energy, mineralnu- acteristicdisturbance regime (the sum of (or a localizedcommunity) is the groupof organisms trients, and species between adjacent the frequencies, intensities, and types of at a specificlocality, and is homogeneousenough to stands, considerable interac- individual A cluster of be considereda unit (Greig-Smith1964, Daubenmire indicating disturbances). 1968).The ecosystem concept--organismsand their stands or a "stand cluster," therefore, encompassingabiotic environment-may be applied has a disturbanceregime cluster, which at any level of spatialscale (Odum1971). However, in turn is constant the in practiceone looks for relativehomogeneity so as fairly throughout to characterizean ecosystem with a limitednumber Formanis with the Departmentof Botany, Rutgers landscape. Disturbances include both of measurements(Woodwell and Whittaker 1968, University, New Brunswick, NJ 08903. Godron is naturalevents and humanactivities such Forman1979a, Bormann and Likens 1980).Though with the Centre d'Etudes Phytosociologiques et one may applythe ecosystem concept to a heteroge- Ecologiques,CNRS, B. P. 5051, Route de Mende, as fire, hurricanes, agricultural prac- neous regionor landscape,in this articlewe limitits 34033Montpellier, France. tices, or forest cutting. use to stands within a landscape.

November 1981 733 species exhibits an aggregated or clus- A. SPOT DISTURBANCE D. INTRODUCED PATCH An environmental patch re- tered distributionof individuals(Chessel PATCH flects the normalheterogeneous distribu- DISTURBANCE 1978, Greig-Smith1964, Kershaw 1973), INTRODUCEDBY PEOPLE tion of resources in the environments and even in randomand regular species 0000111110000 o000111*0000 and results from the environmentalre- of a and distributions,some aggregationsof indi- 8. REMNANT PATCH sources relatively permanent viduals normally are present in a sur- DISTURBANCE DISTURBANCE E. EPHEMERAL PATCH discrete area which differ from the sur- roundingarea of lower density (Godron +++ iTIME4 roundingarea. Unlike the other patches, OOOOO1eenon=n OO oo0000000Qo 1966, 1971). This basic aggregationpat- the environmentalresource patch is not tern of individualsof a species underlies C. ENVIRONMENTAL dependent on disturbance. Concentra- the patchiness of vegetation and animal RESOURCE PATCH tions of amphibians and reptiles in a communities so commonly seen in desert oasis, patches of heaths on an nature. t oooooooooooo exposed mountain ridge, acid-tolerant RESOURCEft In simplestterms, patches are commu- mosses in a glacier-causedbog, and pol- nities or species assemblagessurrounded Figure 1. Patch origins. Species dynamics linatorsin a moist alpine gully are exam- a matrixwith a dissimilar withina patch and turnoverof the patch itself Other examples are described by by community differ to the mecha- ples. structureor The matrixex- substantiallyaccording Brown MacArthur and Wilson composition. nisms causing a patch. 0 0 0 = matrix; (1971), hibits several characteristicsitself, such 0 0 0 = patch; disturbance = a sudden (1967), Simberloff(1976), Smith (1974), as the degree of heterogeneity and con- severe environmentalchange. Stiles (1979),and Willis (1974). Since the nectivity, but in this article we focus on cause of the environmental resource patches and the other structuralcompo- mechanism. This patch is a remnant of patch is relatively permanent,the patch nents, corridors, networks and habita- the previous community embedded in a is permanent,and species changes sim- tions. We further limit the analysis to matrix that has been disturbed. Exam- ply reflect those normal in the interac- patches at a single level of scale, the ples of remnantpatches are woodlots in tion between a small community in dy- landscape, though most of the resulting an agriculturalarea, a shrub-coveredis- namic equilibrium with a surrounding patternsappear to apply to all levels of land produced by flooding a valley, a matrixcommunity. scale. breedingwarbler community on a south- An introduced patch is dominated by facing slope that survived a rare freeze, an aggregationof individualsintroduced or a pocket of that escaped into a matrix by people. Pine and euca- PATCHORIGINS the invasion of an aggressive non-native lyptus plantations (Pinus, Eucalyptus), Further are described fields of wheat and corn Causal Mechanisms species. examples golf courses, by Galli et al. (1976), Gottfried (1979), (Triticum,Zea), or a largefeeding station Five causal mechanisms predominate Helliwell (1976), Pollard et al. (1974), that attractsvertebrate species to a small and the five types of patches produced Seignobos (1978), and Southwood area are examples. Introduced patches differ strikingly in their dynamics and (1961).If the disturbancein the matrixis remainas long as the humandisturbance stability (Forman 1979b). A spot distur- temporary,succession will proceed until regime maintainsthem. Thereafter, spe- bance patch results from disturbanceof the matrix converges with the patch in cies from the matrix colonize, and like a small area in the matrix(Figure 1). For species similarity. Here again the patch the spot disturbance patch, the patch example, patches are produced by a disappears.If this convergence is rapid, disappears as it converges with the small fire in a grassland, a large blow- the patch may change relatively little in matrix. down in a forest, overgrazingby a local species composition. However, if the An ephemeral patch is a transient ag- explodingpopulation of rodents, or local disturbance of the matrix is chronic, gregation of species caused by normal spraying of a generalized insecticide. inhibitingthe normal successional rate short-lived fluctuations iri resource lev- Otherexamples are given by Heinselman and direction, the patch will remain. In els, that is, levels of biotic or abiotic (1973), Levin and Paine (1974), Pickett this case, a net loss of species may take environmentalchange that are frequent and Thompson (1978), and Forman and place (Diamond 1972, Willis 1974). This enough and of a low enough intensity Boerner (1981). Following the distur- hypothesized net loss would be rapid at that species have adaptedto them. Espe- bance, succession proceeds until the first, finallydropping to zero, a response cially rare or severe environmental patch disappears by becoming like the referred to as a relaxation period. The changes are considered disturbances, matrix;that is, changes and species lost are those requiringa which in turn cause spot disturbanceand immigrationsand extinctions of species larger than the remnant patch or those remnantpatches. Examples of ephemer- take place until the relative abundances sensitive to a modified microenviron- al patches are mammalsfeeding at dawn of the species are similarto those of the ment within a patch. arounda large savannamudhole, a local- surroundingmatrix. In unusual cases, Hence, remnant patches vary from ized bloom of annuals in the desert, or a especially where the intensity of distur- short-lived,as producedby a single natu- large shrubbyarea in field-to-forestsuc- bance is severe or the matrixis undergo- ral or human disturbance,to long-lived, cession. However, the rapid-turnover ing rapidchange, succession may lead to resulting from chronic human distur- ephemeral patch appears more promi- a semi-stable patch that differs signifi- bance. In the same way, spot distur- nent at finer levels of scale than the cantly from the matrix. The spot distur- bance patches may be short- or long- landscape. bance patch typically has high popula- lived. In remnant patches caused by In summary,patch is a spatialconcept tion changes and species immigration chronic disturbance,the net loss of spe- focused on a small area. Both the causal causes its ultimatedisappearance. cies duringa relaxationperiod results in mechanismsof patches and the resulting A remnant patch is caused by wide- the patch remaining,but with a species dynamics of patches differ greatly. As spread disturbance surroundinga small composition differing from the original with most biological patterns, some area, the inverse of the spot disturbance patch. overlaps exist amongthe five basic patch

734 BioScience Vol. 31 No. 10 origins. For example, a severe chronic S = f(habitatdiversity ? disturbance+ from habitat diversity. When patch area disturbance in the matrix might so area - isolation + age) alone is evaluated, we find it to be an the matrixthat with determinantof diversi- change convergence Patches in the important species a remnant is landscape, however, ty, and that (such as patch community prevent- differ from islands sur- species groups ed, and the remnant into significantly trees, seed-eating birds and insectivo- patch develops rounded water an environmentalresource by (Forman 1979b). rous birds) respond differently to patch patch. we and Above, analyzed patch origins area (Elfstrom1976, Formanet al. 1976). here note that average turnover rates Other Characteristics (the appearance and disappearance)of be whereas PATCHEDGE AND SHAPE A multitude of possible community landscapepatches may high, named islands are essentially permanent. Simi- The microenvironmentin the center of types, primarilyby physiognomy the of the bound- or predominantspecies, may character- larly, sharpness patch a tiny patch of woods differs strikingly ize in a The number ary varies greatlyin the landscape(Whit- from the center of an extensive woods. patches landscape. taker and of such different is a 1973), gradual gradients may This results largely from penetrationof community types be more conducive to the movement of structural characteristic of land- air from the surroundingmatrix through- key between and matrix. The not for but to species patch out the tiny woods, whereas this air scapes, only mapping, of the matrix is an index of the of biotic heterogeneity landscape penetrates only a limited distance into provide range often which a source richness, and nutrientand high, implies large the edge of the extensive forest. The , of in the matrixand direc- water fluxes in a species strong outer band of a patch, which has an landscape. tional effects of the matrix on different In addition, each environment significantlydifferent from ecosystem compo- sides of the The matrix nent is normallypatchy in the landscape. patch. landscape the interiorof the patch, is known as the For of soil may be used as a rest stop for many This an example, superimposingmaps between patch edge. produces edge ef- tree communities, and herbivo- species moving patches, partic- fect, that is, a differencein species com- types, in the area of a rous mammal communities for a land- ularly limited landscape position and abundancein the edge. For with extensive oceanic archi- scape may show several places where compared example, differences between the edge boundaries coincide and pelagoes. Here the importanceof isola- and interior of deciduous forests in many places a central characteristic of where do not. The of con- tion, island North America and Europe have been they degree is lessened. in the units of differ- biogeographictheory, documentedfor a host of meteorological gruity space among Withina the rain" ent is useful in landscape, "species factors, vegetational characteristics(Ja- components mapping, be and of land- appearsto high, that is, most species kucs 1972,Wales 1967, 1972),and animal planning, analyses reach most within their life structure(Forman 1979b, patches cy- communities(Galli et al. 1976, Johnston scape McHarg cle. when extinctions 1969). Therefore, species 1947, Leopold 1933, Patton 1975). Soil take in recoloniza- place patches, rapid and fire characteristics probably also tion is facilitated and the effect of isola- differ. PATCHSIZE tion minimized.While this species rainis Several factors affect the width of the to be for a as nutrient and water flux, suggested high community, patch edge. The angle of the sun plays a Productivity, measured a rela- and are all affected by , major role, with edges facing equator- species dynamics by small of individual the size of Island tively proportion spe- ward typically wider than those facing landscape patches. cies has a within from limited dispersability poleward(Wales 1972),and those in tem- biogeographic theory developed the Isolation in the in a matrix of landscape. landscape perate areas wider than in tropicalareas. studying archipelagoes be critical for these individual water lends into the may spe- Wind also exerts a majorinfluence, with insight relationship of which are uncommon. between and area. The number cies, many the prevailingwind direction duringthe species in conservation not must the of (= on an Thus, only active or growth period having a wider species, S, species diversity) basic be island was related to three fac- communitypattern considered, edge than other sides. The degree of directly but also the tors in order: the island area, its isola- specific (Dia- species differencebetween the patch and mond and 1976, Formanet al. 1976, tion, and its age (MacArthurand Wilson May matrixis significant,too. Pickett and 1978, Simberloff 1967). The basic island area effect, Thompson The patch edge appears to vary in is due to habitat diversi- 1976, Terborgh 1976). Summarizingthe width from a few meters to a few tens of though, mainly for ty; in most cases, larger islands simply species diversity patterns landscape meters in patches at the landscapelevel. we have more which, therefore, patches suggest: Different groups of organisms respond to the environmentallydeter- supportmore species. However, there is S = f(habitatdiversity + disturbance+ differently also an area effect: When the habitat area + age + matrix heterogeneity mined edge width. For example, in diversity of large and small islands or - isolation - boundary discreteness) woodlots, avian and tree communities patches does not differ, more species are appearto differfrom the interioronly in typicallyfound on the former(Forman et Landscapepatch area has been shown the outer portion of a forest edge, while al. 1976,Simberloff 1976). Finally, one of to correlate strongly with species diver- herbs and mosses appear sensitive to the major factors determiningdiversity sity (Galli et al. 1976, Gottfried 1979, essentially the entire edge width. on an island or patch is the history and Moore and Hooper 1975, Peterken 1974, Patch shape as a variableis important present regime of disturbance(Carlquist Robbins 1980,Whitcomb 1977), but rare- in several ways, such as a target for 1974,Pickett and Thompson 1978).Sum- ly has area been considered separate dispersalor home range suitability;here marizingthe patternsfor islands, species we consider patch shape in the context - = diversity is a function of certain island 2+ = positively related to diversity; negatively of the edge concept. A large isodiametric related;+ = usuallynegatively, but sometimespos- characteristics listed in the suggested itively, related. Units are not considered in this patch is mostly interior, with a band of order of overall importance:2 encapsulation. edge in the outer portion of the patch. A

November 1981 735 rectangularpatch of the same size has PATCHNUMBERS A. SIZE B. SHAPE C. BIOTIC TYPE D. NUMBER proportionally less patch interior and AND CONFIGURATION 0o o more a narrow @ @ o patch edge. Finally, strip 0 o patch of the same size may be all edge. So far we have focused on the charac- Since communityand populationcharac- teristics of individual patches. Patches, teristics differ between the interior and however, do not exist generally singly, E. CONFIGURATION the these characteris- but vary in numbersand in their config- 1) Distance Size Shope Biotic Type Origin edge, comparing Apart Difference Difference Difference Difference tics with the interior to edge ratio of urationand juxtaposition to one another. patches may be useful in evaluating the Patches exhibitingany of the above de- 0 0- 0 Introduced importance of patch shape in a scribed patch characteristics may, of from zero to in a landscape. course, vary many 2) Regular Random Aggregated

Whitmore noted that In a land- 0000 00oo (1975) plant spe- landscape. understanding . o 0 0 o 0 00 0 0o ooo S08 ooooo0 o cies composition and community struc- scape, determiningthe numberof patch- introducd ture varied according to the shape of es in each of at least four categories o 0 Ooo in rain forests. Stiles essential. How ) Disitance SiNegate ShapDendritic Liner Circuiginor openings tropical appears many patches % 0 0 0 0 .0. (1979) found sharp differences in wasp are there of each of the patch origins? 0 nesting density in the New Jersey Pine How many of each communitytype are 0 Barrens to the width of the there for each of the origins? In according patch Figure 2. Patch characteristics in a habitat.In Idaho rockslides, small mam- each category thus formed, what is the landscape. mal density correlated best with the size distribution of the patches? And lengthof the rockslideperimeter (Bunnel what is the distributionof patch shapes and Johnson 1974). Unpublished data in each of these? boundaries,drainage ditches, and irriga- (Formanand Clay) on mushroomdiver- Determining the numbers in each of tion channels, are narrow and typically sity in old New Jersey two-hectare oak these four categories is not difficult in have only species characteristicof patch woodlots indicate a halving of species some landscapes. A subsamplecan then edges. Strip corridors are wider bands diversity and a threshold response in be selected for measurementof the spe- containinga patch interior environment proceeding from isodiametric through cies, energy, or nutrient component of in which interiorspecies may migrateor rectangularto strip patches. Patch width interest, and by simple multiplicationthe live. Stream corridors, which border wa- or shape, therefore, appears to be a status of the componentin the patches of ter courses and vary in width according major ecological variable in the a landscape can be estimated with a to the size of the stream, control water landscape. measure of variability. However, this and mineral nutrient runoff, minimizing Several special cases of shape bear estimation is inadequate, because the flooding, siltation, and soil fertility loss. mention. Ring zones are belts of vegeta- spatial configurationamong the patches Networks are formed by intersectingor tion, commonlywithin a particularaltitu- has been ignored. For example, a land- anastomosing corridors and therefore dinal range, which extend around a scape with ten evenly-distributedlarge contain loops. Some overlap among the mountain, and contain a "hole" with patches differs fundamentally in most four basic types exists, such as edge differentvegetation at a differentaltitude ecological fluxes from a landscape with species moving in all four, or a wide (Hedberg 1955, MacArthurand Wilson the ten patches clustered at one end. stream corridor also functioning as a 1967).The interiorto edge ratio indicates Various spatial configurations(Figure strip corridor for movement of patch that ring zones are more similar to strip 2) can be examinedusing standardstatis- interiorspecies. patches than isodiametricpatches. Lin- tical techniques (Chessel 1978, Daget Line corridorsare particularlycharac- ear patches and dendritic patterns con- 1979, Godron 1971, Kershaw 1973) ap- teristic of landscapes dominated by hu- tain special characteristicsand are con- plied to the distribution of patches in man disturbance. They originate in the sideredbelow. each of the categories just described. same ways as patches, e.g., remnanttree The peninsula,where a narrowportion The patches of a category may be ran- lines left between fields from an earlier projectsfrom a large patch, is a common dom, regular, or aggregated;or positive forest, paths as spot disturbance lines, shape, and species diversity commonly or negative associations among patches and introduced lines as shrub and tree decreases progressively toward the tip. of different categories may be present. plantings for defense, enclosing live- The reason for this pattern in major This provides insight into both the cause stock or decreasingwind (Kellogg 1934, continentalpeninsulas of North America of the patches and the potentialfor inter- Rotzien 1963, Seignobos 1978, Van Ei- is hypothesized to be species extinction patch interaction.For example, common mern et al. 1964). on the peninsula during the Pleistocene nonrandompatterns of patches are seen The plant and animal species of line and subsequent gradual recolonization in limestone karst topography, in den- corridors generally also characterize from the continent (Simpson 1964, Tay- dritic stream basins, along roads and patch edges (Pollard et al. 1974). These lor and Regal 1978). An alternative ex- property lines, or encircling towns. Fi- corridors provide habitat and breeding planationbased on the edge effect, that nally, the actual distance between patch- sites for species requiringthe surround- the peninsularedge has a climate strong- es is an importantmeasure of potential ing matrixenvironment for protectionor ly modified by the surroundingwater patch interactions. feeding. Introduced nonnative species leavinglittle if any interiorenvironment, are common in line corridors,especially the disturbance-causedcorridors. is well known to farmerswho must grow CORRIDORS different crops on peninsulas (e.g., The microstructureof the line pro- functions Squier 1877). Apparentlythe peninsular There are four types of corridors in vides insight into its potential effect has not been studied at the land- landscapes: Line corridors, such as (Les Bocages 1976, Lewis 1969, Pollard scape patch level. paths, roads, hedgerows, property and Relton 1970, Pollard et al. 1974,

736 BioScience Vol. 31 No. 10 Southwood 1961). Hence, a path line scapes with ample human activity, one HABITATIONS contains mainly disturbance-resistant type of corridor, such as a road, com- species and has compacted soil, often monly crosses another type, such as a A final major structuralcharacteristic with attendanterosion along the line. In hedgerow. The degree to which such of many landscapesis humanhabitation, contrast, the hedgerow line of shrubs or crossings are effective barriers to the including the house with its associated trees, which is higher than the matrix, migration of different species needs yard, courtyard,farm buildings and im- cuts wind velocity, shades the adjacent study. mediate surroundings. Habitations, of matrix, and has a high evapotranspira- The corridormay exist as an isolated course, are disturbance-caused,partially tion rate. Irrigationchannels, and often unit or it may interconnectpatches in the or totally eliminatingthe naturalecosys- roads and hedgerows, include adjoining landscape. In patches, species become tem at that spot. The continued exis- ditches and embankmentswith consider- extirpatedfor many reasons. Following tence of the habitationdepends on main- able microhabitat diversity where am- loss of a species in a patch, a connected taininga chronic disturbancelevel. phibians,reptiles, and moisture-tolerant corridorfacilitates rapidreestablishment The primary ecological structure of plants are often favored. Changes in line of certain species in the patch. A strip habitationsis based on the types of or- corridorsthrough time are little known. corridor that links small patches may ganisms that have replaced the naturally M. D. Hooper, however, found a linear enrich those patches with species that occurring ones. Foremost are people, correlation between hedgerow age and otherwise could not survive in small iso- who provide the continued disturbance shrubspecies diversity in managedBrit- lated patches, because many species regime to maintain the habitation area. ish hedgerows, with an average one spe- have minimumpatch size requirements Most of the plants, in turn, are intro- cies gained per century (Les Bocages for survival (Galli et al. 1976, Robbins duced by people. Some may be native 1976, Pollardet al. 1974). 1980, Terborgh1976). Additionally,cor- species, but humansexhibit a propensity General characteristics of the wider ridors facilitate gene flow across the for surroundingthemselves with a di- strip corridors are reasonably well landscape. verse and exotic species assemblage. known, despite a paucity of direct stud- Networks are particularlywidespread People also generally introduce domes- ies. The corridor must provide protec- in landscapes bearing the heavy imprint tic, rather than native animals into tive cover for species from naturalpred- of human activity. Anastomosing line homes, and both animal and plant pests ators, domestic animals, and human corridors generally form networks, are inadvertently introduced. Native effects lining each side of the corridor. though occasionally networks may be species from the surroundingmatrix or The outer portions of the strip corridor composed of strip corridors. Familiar patches immigrateinto habitationareas, have the edge effect, while the central examples are the interconnectedhedge- but their success depends upon the level portion contains the interior environ- rows or "bocage" and the networks of of disturbancemaintained. ment required for many patch interior roads and railroads. A few networks Distance between habitationsin effect species (Andersonet al. 1977,Johnson et reflect natural conditions, such as the defines urban, suburban, town, village, al. 1979).For this reason, the width of a polygon soils of arctic tundra areas or and various rural areas. The greatest stripcorridor is critical, since the interior the reticulate trails of large mammalsin density and diversity of introducedspe- environmentmust be present and suffi- east African savannas. cies appears, on the average, in subur- ciently wide itself to be used by interior As isolated units, single corridorsare ban areas, and indeed, in all areas with species. consideredto enhance the movement of contiguous homes, the ecosystem is In contrast to the line and strip corri- species. However, as a series of inter- dominated by humans and introduced dors, the stream corridor is normally a connected links and loops, a network species (Schmid 1975). In rural areas dendriticpattern formed by intersecting provides a more efficient migratorysys- with isolated homes, the entire borderof narrowfingers upstream which gradually tem, since alternativepathways are pre- the habitation interfaces with patches, widen downstream.The stream corridor sent. This structureis importantfor ani- networks, corridors or the matrix, so is the most widespread corridor type, mal efficiency, predator that interactionwith other landscapeele- and the concept has developed from con- avoidance, and minimizingthe barrieror ments is at a maximum.This interaction siderationsof water and mineralnutrient isolating effect of a local disturbanceor is the primaryecological importance of flows. This corridor strongly affects the break in a corridorlink. The frequency habitationsin rurallandscapes. erosion rate of the stream banks and of intersections of corridorsand the de- adjoiningupland and the absorptionrate gree to which such intersections are ex- of water from precipitation and runoff. panded nodes or patches may play an DYNAMICSOF THE LANDSCAPE These, in turn, control siltationand flood important role in migration efficiency. levels in downstream ecosystems. The Some networks, such as paths and Our primaryobjective in this article is streamcorridor is optimumwhen it dou- roads, are especially effective for move- to lend insight into the ecological struc- bles as a strip corridorfor the migration ment of people and domestic animals. ture of landscapes, particularlypatches of interior species. Since many species We hypothesize networks to be impor- (Figure3). Yet, the structureis ultimate- cannot survive the occasional floods of tant migrationroutes for native species, ly of importanceas it relates to function. the streamlowland or the wet soils of the but as yet, the evidence is meager (Pol- We have touched on the dynamics of lowland and adjoiningbanks, the corri- lard et al. 1974). patches themselves. Here we brieflysug- dor must include a strip of interiorenvi- In short, networks are prominentfea- gest some examples of fluxes between ronment on well-drained soil atop the tures of most landscapes today. Their structuralcomponents of the landscape streambank. functional importance rests not only in (Forman 1981), that is, interactions be- A corridor should be continuous for movement along the links, but in their tween patch and matrix, patch and patch maximumeffectiveness (Getz et al. 1978, impact on the matrix and patches in the of the same type, patches of different Schreiber and Graves 1977). In land- surroundinglandscape. types, networkand matrix, and the like. November 1981 737 Interactionsbetween patch and matrix isolatedunits. Networks and streamcor- CONCLUSION are in both directions. Heat ridors retard surface water and nutrient important The structureof a landscapeis carried wind from one to the and siltation and primar- energy by runoff, subsequent ily a series of patches surroundedby a other accelerates the floods in downstream and in evapotranspiration ecosystems, matrix. The origins of patches differ ac- rate and desiccates the microenviron- a similar a network modifiesthe fashion, cordingto the disturbanceregime in the ment for certain wind flow of air and heat over the species. Similarly, energy patch, disturbancein the matrix, natural carries and which in turn alters moisture, ash, dust, propa- landscape, evapo- distributionof environmentalresources, back and forth. Fire and other and the moisture gules transpiration patterns species introductions by people, and disturbancesstart in one and enter the of the soil. time. These differences in patch origin and of animals as other, many types forage Finally, habitations, species determinethe dynamics and the from one to another. and nonnative species sources, provide people stability and turnover of patches Corridors and networks facilitate plants and animals. They, in turn, har- themselves. movementof from to vest form corridors and net- species patch patch species, Patch area, and secondarily isolation, in the but also a various landscape, play major works, produce disturbances, have traditionallybeen considered the role in of matrix and colonize both the inhibiting migration surroundingpatch- major variables indicating the species the matrix into es and matrix. species by subdividing diversityof a patch. We hypothesize that species diversity in a landscape patch is 47? ~ a function of varia- :: . the following patch ~~UP, bles in orderof overall importance:habi- tat diversity ?+disturbance + area + age + matrix heterogeneity - isolation - boundarydiscreteness. Patch shape as a modifierof area is importantto species diversity and is mediated through the ...... "" patch edge or edge effect. The numbersof patches of each patch origin,biotic patch type, size, and shape determine in part the landscape struc- ...... -- i7 ture. However, the spatial configuration among the patches present may be just as importantas the numbers. Corridorsvary in width and function. Line corridors,particularly those result- ::7f7 ing from human activities, are very nar- row and used primarilyfor movement of edge species or people. Strip corridors, for effective movement of species char- acteristic of the interior of a patch, are wide enoughto include an interiormicro- environment as well as edge effect on both sides. A special case is the stream corridor,which also controls water and nutrientflows across the landscape. Networks composed of intersecting corridorsare prominentfeatures of most landscapes. Networks provide an effi- cient migratoryroute as well as alter the flow of nutrients, water, and air across the landscape. Portionof an in New for corn and Figure 3. agriculturallandscape Jersey. Farmingpractices The of in beans since 1701 have moldedthis landscape. Limitedsuburbanization effects are recent. The concept repetitive patterns geomorphologyis a level Triassicred shale, on whicha well-drainedsilt loam of the Penn series the structureof landscapes opens up a predominates.The biotic patch types present are dominated by white, red and black oak host of ecological questions related to (Quercusalba, Q. borealis,Q. velutina),except in streamcorridors and wet spots where pinoak, both structure and function, and pro- red ash and elm Acer maple, (Q. palustris, rubrum,Fraxinus, Ulmus) predominate. Photograph vides a relatively simple frameworkfor taken May 29, 1970. A. Spot disturbance patch (small opening in forest). B. Strip corridor (powerlinecrossing stream corridor).C. Narrowpatch with no forest interior.D. Stripcorridor testing them. It also provides a land (wooded).E. Tinypatches withno forest interior.F. Peninsula.G. Tinyremnant patch affected by managementtool for helping to deter- proximityto largerpatch. H. Introducedpatch (golf course). I. Introducedline corridor(Platanus mine prioritiesin the land use. Finally, it plantedalong road). J. Large remnantpatch (well-developedforest interior;patch edge about emphasizes that no patch stands alone. twiceas wide to south as north).K. Road network.L. Dwellingsclustered (village). M. Introduced patch (cemeteryconifers and grass). N. Environmentalresource patch (lowlandtree species on wet spot). 0. Temporalpatch (area of shrubs and successional trees undergoingrapid change). ACKNOWLEDGMENTS R. Matrix P. Wide stream corridor(containing both riverand canal). Q. Narrowstream corridor. We thank Steward T. A. Pickett and (corn and bean fields). S. Line corridor(road). T. Habitation(area of farm buildings). U. Hedgerownetwork (connecting woods patches). V. Small remnantpatch (containslimited area MarkJ. McDonnell for significantlyim- of forest interior). provingthis manuscript,and the Nation-

738 BioScience Vol. 31 No. 10 al Science Foundationfor grantDEB-80- within differentsized forest islands in cen- Moore, N. W., and M. D. Hooper. 1975. On 04653 in support of a portion of this tral New Jersey. Auk 93: 356-364. the number of bird species in British work. Getz, L. L., F. R. Cole, and D. L. Gates. woods. Biol. Conserv. 8: 239-250. 1978. Interstate roadsides as dispersal Odum, E. P. 1971. Fundamentals ofEcology. REFERENCESCITED routes for Microtus pennsylvanicus. J. W. B. SaundersCo., Philadelphia,PA. Anderson, S. H., K. Mann, and H. H. Shu- Mammal. 59: 208-212. Patton, D. R. 1975. A diversity index for gart, Jr. 1977. The effect of transmission Godron,M. 1966.Application de la th6oriede quantifyinghabitat edge. Wildl. Soc. Bull. line corridors on bird populations. Am. l'informationA l'6tude de l'homogdn6it6et 394: 171-173. Midl. Nat. 97: 216-221. de la structure de la v6gdtation. Oecol. Peterken,G. F. 1974. A method of assessing Bormann, F. H., and G. E. Likens. 1980. Plant. 2: 187-197. woodlandflora for conservationusing indi- Pattern and Process in a Forested Ecosys- 1971. Essai sur une approche proba- cator species. Biol. Conserv. 6: 239-245. tem. Springer-Verlag,New York. biliste de l' cologie des vegetaux. These Pickett, S. T. A., and J. N. Thompson. 1978. Brown, J. H. 1971. Mammalson mountain- d'Etat, Univ. Sci. Tech. Languedoc,Mont- Patch dynamics and the design of nature tops: non-equilibriuminsular biogeogra- pellier, France. reserves. Biol. Conserv. 13: 27-37. phy. Am. Nat. 105:467-478 Gottfried,B. M. 1979.Small mammalpopula- Pollard, E., M. D. Hooper, and N. W. Bunnell, S. D., and D. R. Johnson. 1974. tions in woodlot islands. Am. Midl. Nat. Moore. 1974. Hedges. W. Collins Ltd., Physical factors affecting pika density and 102: 105-112. London. dispersal. J. Mammal. 55: 866-869. Greig-Smith, P. 1964. Quantitative Plant Pollard,E., and J. Relton. 1970. Hedges V. A Carlquist,S. J. 1974.Island Biology. Colum- Ecology. Butterworths,London. study of small mammals in hedges and bia Univ. Press, New York. Grossman, L. 1977. Man-environmentrela- cultivated fields. J. Appl. Ecol. 7: 549-557. Chessel, D. 1978. Descriptionnon paramdtri- tionships in anthropologyand geography. Robbins,C. S. 1980.Effect of forest fragmen- que de la dispersion spatiale des individus Assoc. Am. Geogr. Ann. 67: 126-144. tationon birdpopulations. Pages 198-212in d'une esp~ce. Biometrie et Ecologie 1: 45- Hedberg, 0. 1955. Vegetation belts of the R. M. DeGraaf and K. E. Evans, compil- 135. East African mountains. Sven. Bot. Tidskr. ers, Management of North Central and Daget, P. 1979. La nombre d'espces par 45: 140-202. NortheasternForests for Nongame Birds. unit6d'6chantillonnage de taille croissante. Heinselman, M. L. 1973. Fire in the virgin U.S. Dep. Agric. For. Serv., Gen. Tech. La Terre et la Vie 32: 461-470. forests of the Boundary Waters Canoe Rept. NC-51. Daubenmire, R. 1968. Plant Communities: A Area, Minnesota.Quat. Res. (NY) 3: 329- Rotzien, C. L. 1963. A cumulativereport on Textbook of Plant Synecology. Harper and 382. winter bird populationstudies in eight de- Row, New York. Helliwell, D. R. 1976. The effects of size and ciduous shelterbeltsof the Red River Val- Diamond,J. M. 1972. Biogeographicalkinet- isolation on the conservation value of ley, North Dakota. Proc. ND Acad. Sci. 17: ics: estimationof relaxationtimes for avi- wooded sites in Britain. J. Biogeogr. 3: 19-23. faunas of southwest Pacific islands. Proc. 407-416. Sauer, C. 0. 1963. The morphologyof land- Nat. Acad. Sci. USA 69: 3199-3203. Isard, W. 1975. Introduction to Regional Sci- scape. Pages 315-350 in J. Leighly, ed. Diamond,J. M. and R. M. May. 1976. Island ence. Prentice-Hall,New York. Land and Life: A Selection from the Writ- biogeographyand the design of naturalre- Jakucs, P. 1972. Dynamische Verbindung der ings of Carl Ortura Sauer. University of serves. Pages 163-186 in R. M. May, ed. Walder und Rasen. Akad. Kiado, Verlag CaliforniaPress, Berkeley. . Saunders, Philadel- Ungarischen Akad., Wissenschaften, Schmid, J. A. 1975. Urban Vegetation: A phia, PA. Budapest. Review and Chicago Case Study. Depart- Dickinson, R. E. 1970. Regional Ecology: Johnson, W. C., R. K. Schreiber, and R. L. ment of Geography,University of Chicago, The Study of Man's Environment. John Burgess. 1979. Diversity of small mammals Chicago, IL. Wiley & Sons, Inc., New York. in a powerline right-of-way and adjacent Schreiber, R. K., and J. H. Graves. 1977. Elfstrom, B. A. 1976. Tree species diversity forest in east Tennessee. Am. Midl. Nat. Powerline corridorsas possible barriersto and forest island size on the Piedmont of 101:231-235. the movement of small mammals. Am. New Jersey. M.S. thesis, Rutgers Univ., Johnston, V. R. 1947. Breeding birds of the Midl. Nat. 97: 504-508. New Brunswick,NJ. forest edge in Illinois. Condor49: 45-53. Seignobos, C. 1978. Les systhmes de d6fense Forman, R. T. T., ed. 1979a. Pine Barrens: Kellogg, R. S. 1934. The shelterbeltscheme. vdgdtaux pr6-coloniaux. Annales de l'Uni- Ecosystem and Landscape. Academic J. Forestry 32: 947-977. versite du Tchad. Serie Lettres, Langues Press, New York. Kershaw, K. A. 1973. Quantitative and Dy- Vivantes et Sciences Humaines. Numdro . 1979b. The Pine Barrens of New namic Plant Ecology. American Elsevier Spdcial.Tchad. Jersey: An ecological mosaic. Pages 569- Publishers,Inc., New York. Simberloff,D. S. 1976. Experimentalzooge- 585 in R. T. T. Forman, ed. Pine Barrens: Leopold, A. 1933. Game Management. ography of islands: Effects of island size. Ecosystem and Landscape. Academic CharlesScribner's Sons, New York. Ecology 57: 629-648. Press, New York. Les Bocages: Histoire, Ecologie, Economie. Simpson, G.G. 1964. Species density of . 1981. Interactions among landscape 1976. Universit6Rennes, Rennes, France. North American recent mammals. Syst. elements: a core of . In Levin, S. A., and R. T. Paine. 1974. Distur- Zool. 13: 57-73. Perspectives in Landscape Ecology. Proc. bance, patch formation, and community Smith, A. T. 1974. The distributionand dis- Int. Congr.Landscape Ecol., 1981,Veldho- structure. Proc. Nat. Acad. Sci. USA 71: persal of pikas: Consequences of insular ven. Pudoc Publ., Wageningen,The Neth- 2744-2747. population structure. Ecology 55: 1112- erlands,in press. Lewis, T. 1969. The distributionof insects 1119. Forman, R. T. T., A. E. Galli, and C. F. neara low hedgerow.J. Appl. Ecol. 6: 443- Southwood, T. R. E. 1961. The number of Leck. 1976. Forest size and avian diversity 452. species of insect associated with various in New Jersey woodlots with some land use MacArthur,R. H., and E. O. Wilson. 1967. trees. J. Anim. Ecol. 30: 1-8. implications. Oecologia (Berl.) 26: 1-8. The Theory of Island . Squier, E. G. 1877. Peru: Incidents of Travel Forman, R.T.T., and R. E.J. Boerner. PrincetonUniversity Press, Princeton, NJ. and Exploration in the Land of the Incas. 1981. Fire frequency and the Pine Barrens McHarg, I.L. 1969. Design with Nature. Holt, Rinehart& Winston, New York. of New Jersey. Bull. Torrey Bot. Club 108: Natural History Press, Garden City, New Stiles, E. W. 1979.Animal communities of the 34-50. York. New Jersey Pine Barrens. Pp. 541-553 in Galli, A. E., C. F. Leck, and R. T. T. For- Mikesell, M. W. 1968. Landscape.Int. Ency- R.T.T. Forman, ed. Pine Barrens: Ecosys- man. 1976. Avian distribution patterns clo. Soc. Sci. 8: 575-580. tem and Landscape. Acad. Press, NY. November 1981 739 Taylor, R. J., and P. J. Regal. 1978. The peninsulareffect on species diversity and the biogeographyof Baja California.Am. Informationfor Contributors Nat. 112:583-593. Terborgh,J. 1976. Island biogeographyand conservation:Strategy and limitations.Sci- * Correspondence: Allcorrespondence should be directedto BioScience, AmericanIn- ence 193: 1029-1030. stitute of BiologicalSciences, 1401 WilsonBlvd., Arlington, VA 22209; 703/527-6776. Van R. L. A. Razu- Eimern, J., Karshon, * Editorial Policy: The editors welcome manuscriptssummarizing important areas of mova, and G. W. Robertson. 1964. Wind- biologicalinvestigation, written for a broad audience of professional biologists and ad- breaks and shelterbelts. World Meteorol. vanced students. We also publish commentarieson BioScience articles, or on other Organiz.Tech. Note No. 59. 188 pages. articles, or on currentissues in the life sciences. In addition,we publish editorialsor Wales, B. A. 1967.Climate, microclimate and short statements of opinion. vegetation relationships on northern and * Editorials must not exceed 600 words. southernforest boundariesin New Jersey. * must not 5000 about five BioScience WilliamL. Hutcheson Mem. For. Bull. 2: Articles and Commentaries exceed words, titles as short as consistent with The 5000-word count 1-60. pages. Keep possible, clarity. does not allow for illustrations and tables, so text length must be adjusted to ac- 1972. Vegetation analysis of north- commodate them. The editors reserve the rightto edit the manuscripts;alterations ern and southern edges in a mature oak- will not be made withoutauthor permission. hickoryforest. Ecol. Monogr. 42: 451-471. Papers are accepted for publicationon the conditionthat they are submittedsolely to Whitcomb,R. F. 1977. Island biogeography BioScience and thatthey willnot be reprintedor translatedwithout the consent of the edi- and "habitat islands" of eastern forest. tors. As the publisher,the AIBS requiresan assignment of copyrightfrom all authors. Am. Birds 31: 3-5. Papers willusually be publishedin the orderof acceptance. The date of acceptance will be withthe article.About six months between of manu- Whitmore,T. C. 1975. TropicalRain Forests published usuallyelapse receipt the Far East. Oxford Press, scriptand publication. of University Authors must obtain written to reprintany copyrightedmaterial that has New York. permission been published elsewhere, includingtables and figures. Photocopies of the permission Whittaker,R. H., ed. 1973. Ordinationand letters must be enclosed withthe manuscriptand creditgiven to the source. Classificationof Communities.Junk Publ., * Referees: Manuscriptswill be reviewedby scientistscompetent in the field.Authors are The Hague. requested to submitthe names and addresses of four potentialauthoritative reviewers Willis, E. 0. 1974. Populationsand local ex- fromoutside theirown institutionbut in NorthAmerica. tinctionsof birdson BarroColorado Island, * of must conformto the Councilof Biology Edi- Panama.Ecol. Monogr. 44: 153-169. Preparation manuscript: Manuscripts tors Manual,4th ed., except for referencestyle (see below). Manuscriptsshould be Woodwell, G.M., and R. H. Whittaker. Style double-spaced throughout,including references, tables, footnotes, 1968. in terrestrialeco- neatly typewritten, Primaryproduction captionsfor illustrations,etc., on one side only of 81/2x 11-inchwhite bond paper. Submit systems. Am. Zool. 8: 19-30. originalplus two copies; the authorshould retaina copy. A separate titlepage should be provided,and footnotes, figurecaptions, and tables should be typed on sheets separate fromthe text. At least one copy must be complete with figures, tables, and references. All weights and measures must be in the metricsystem. * Abstract: An abstractof not more than 50 words must accompany articles and com- mentaries;therefore, a summaryshould not be included. * Illustrations: Illustrationssuch as photographs,maps, line drawings,and graphs must be in "camera-ready"form (i.e., originalart drawnby a commercialartist) and submitted, unmounted,with the manuscript.Number figures consecutively and identifyon the re- ITURTOX verse side. Photographsmust be glossy, black-and-white,and from4 x 5 to 8 x 10 inches (successorto MacmillanScience Co.) in size. Drawingslarger than 8 x 10 are usually not acceptable. Letteringon all illustra- tions must be sufficientlylarge to allowreduction to a double or single columnwidth. Pho- See new addressand phone tomicrographsshould have a scale bar. Figurecaptions for illustrationsshould be typed on separate pages. Colorphotographs for the cover willalso be considered. shorterour name Although * Footnotes: Footnotesin text should be kept to a minimumand should be indicatedby Makingquality slides consecutive superscriptnumerals. Footnotes in tables are representedby symbols (see p. 39, CBE Style Manual, 4th ed.). "Personal communications" are footnotes and Employeesthe same must includename and affiliationof source as well as monthand year of communication. * References: "ReferencesCited" includes literature, published or unpublished,which is retrievableby readers. Citationsin the text are designated by authorname and year of Courteousattention toyour needs publicationin parentheses (Link1928, McNaughtonand Wolf1973) in alphabeticalorder. Offeringslides reasonably priced Use the first author'sname and "et al." for works having more than two authors(Scho- landeret al. 1950), but list all authorsin the references.All works cited in the text must be Minimumorder not required listed in the "ReferencesCited" and vice versa. Use the BIOSISList of Serials for journal abbreviations.BioScience referencestyle does not followthe CBEStyle Manual,4th ed.; Payingshipping on $25.00 or more referto a recent issue of the journal.Some samples are: Automatic5% discount on pre-payment Link,G. K. K. 1928. Bacteriain relationto plantdiseases. Pages 590-606 in E. O. Jordan at and I. S. Falk, eds. The Newer Knowledge of Bacteriology and Immunology.Uni- Now yourservice versity of Chicago Press, Chicago, IL. You'lllike us! Try us! McNaughton,S. J., and L. L. Wolf. 1973. GeneralEcology. Holt, Rinehartand Winston, New York. Scholander, P. F., V. Waiters, R. Hock, and L. Irving.1950. Heat regulationin some arctic and tropicalanimals and birds. Biol. Bull. 99: 236-258. * Reprints: Ordersfor reprintsmay be placed either before or afterthe issue is printed, but must be prepaidor accompaniedby an institutionalpurchase order.Allow four weeks 5000 W. 128thPlace for deliveryafter publication.Minimum order: 50 copies. Alsip,Illinois 60658 312/371-5500

740 BioScience Vol. 31 No. 10