Structure and Function in Agroecosystem Design and Management - Chapter 2 pptx

38 INTRODUCTION The use of biodiversity as a tool to assess landscape structure, transfor-mation, and fate is a valid component of policies applied to rural, managed, industrial, and urb

PART I Biological Interactions in Agroecosystems

CHAPTER 2

Biodiversity in Agroecosystems

and Bioindicators of Environmental Health Maurizio G Paoletti

CONTENTS

Introduction 12

How Many Species on the Planet and How Many Species on the Desk 13

Plurality of Species Bioindicators and the Human Limited Ability to Memorize 15

What Is Biodiversity and How Can It Be Used to Assess the Landscape? 16 What Bioindicators Are and How to Use Them 17

What Is Sustainability? 18

Landscape vs Landscape Structure 21

Margin Effects (Hedgerows, Shelterbelts, Weed Strips) 21

Corridors and Connectivity in the Landscape 23

Effect of Mosaics in the Landscape 23

Colonization and Recolonization Dynamics and Pendularism 25

Hedgerow Isolated 25

Semipermanent Crops 27

Hedgerow Network in the Landscape 28

Grassy Semipermanent Margins, Beetle Banks 30

Complexity of Vegetation and Predation 30

Perennials vs Annual Crops 31

Impact of Pollution 32

Waste Disposal, Reclamation and Rehabilitation, and Bioremediation 33

Soil Tillage and Soil Compaction 33

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Biotechnology: Genetically Engineered Plants 34

Practical Approaches for Field Assessment with Bioindicators to Monitor Decreasing Impact 35

Decreasing Environmental Impact 37

Concluding Remarks 37

Acknowledgments 38

References 38

INTRODUCTION

The use of biodiversity as a tool to assess landscape structure, transfor-mation, and fate is a valid component of policies applied to rural, managed, industrial, and urbanized areas to reduce human mismanagement and alle-viate pollution (Wilson, 1997) The argument for the importance of biodiver-sity in directing environmental policy presupposes that animals, plants, and microorganisms and their complex interactions respond to human landscape management and impacts in different ways, with some organisms respond-ing more quickly and definitively than others It has to be assumed that changes in landscape management influence the biota, and that certain tran-sient or permanent signs remain inside the system of biological communities (Richardson, 1987; Szaro and Johnston, 1996; Jeffrey and Madden, 1991; Paoletti and Pimentel, 1992) This assumption is supported by three recent books summarizing current data on insects as indicators of pollution and environmental change (Harrington and Stork, 1995; Munawar et al., 1995; and Paoletti, 1999) However, much work is needed to directly relate this assumption to the pragmatic problems encountered as attempts are made to improve the living landscape

Disappearance of species is most readily apparent in the case of birds, but-terflies, and mammals; the threatened extinction of such conspicuous organ-isms often raises public concern and garners attention from news media For the most part, knowledge of small organisms remains conceptual, and common knowledge of the relationships between biota and their environments is approximate at best (Table 2.1); the importance of small creatures in food-chains

is poorly understood or ignored (Pimm, 1991; Hammond, 1995; Paoletti, 1999)

In most cases “modern” management of landscapes has supported few key plants (crops) and few animals The agricultural revolution of the last 13,000 years has in general seen efforts concentrated on a limited number of species This process of reducing species numbers is also the common trend

in agriculture, with widespread use of systems in an early succession stage and concentration on a few short cycle plants such as cereals Most citizens living in towns eat a limited variety of plants and animals and are aware of few invertebrates The situation is quite the opposite in some Amazon regions dominated by the forest and/or savannas and populated by hunter-gatherers and horticulturalists (Table 2.1)

Simplification in landscape management in most cases signifies main-taining the first stages of one succession and large numbers of few dominant

species (Odum, 1984) Most applied fields of landscape management, ing agriculture, tend to deal with only a few species: monocultures are therule both in fields and on our desks The majority of today’s scientists, engi-neers, and university-educated professionals are trained to solve a narrowrange of problems and have a limited ability to deal with complex systems(Funtowicz and Ravetz, 1993) Most successful human endeavors haveinvolved reduction of variables (species) with positive economic results, atleast in the short term.

includ-Assessing landscape quality by means of indicators based on sity involves a substantial change in perspective not only by the experts andtechnicians, but also by the public and society in general People who expect

biodiver-a productive, clebiodiver-an, biodiver-and hbiodiver-armonious lbiodiver-andscbiodiver-ape thbiodiver-at cbiodiver-an be sustbiodiver-ained forfuture generations must learn more about the diversity of life and makeefforts to allow cultures that have their base in the plurality of organisms tomaintain their territory and way of life

HOW MANY SPECIES ON THE PLANET AND HOW MANY

SPECIES ON THE DESK

At the moment, no exhaustive data base on living species exists For thisreason, estimations of existing described species oscillate between 1.3 million

Table 2.1 Estimated (maximum) number of species known and consumed as

food by western civilized peoples and forest- and savanna-dwelling peoples in Amazonas (Venezuela) Interviews were performed by university personnel (1995 –1996) using forms filled out in class; oral interviews were carried out in Amerindian villages located near Puerto Ayacucho, Amazonas (1997).

Population Plants Mammals Fishes Birds Insects TOTAL

The Guajibo live in the savannas near P Ayacucho, Amazonas, Venezuela.

The Curripaco are an expert river margin-dwelling group living near P Ayacucho, Amazona, Venezuela The Piaroa and Yanomamo are more strictly forest-living Amerindians in the Alto Orinoco, Amazonas, Venezuela The Yanomamo maintain strong links with the forest for their survival.

*Based on different sources and evaluations, the total number could be around 1400 species.

(Wilson, 1988; Wheeler, 1990) and 1.8 million (Stork, 1988) The large majority

of the estimates represent small creatures, especially invertebrates However,forecast species are some orders of magnitude even more abundant on theplanet Terry Erwin (1982) first documented the incredible projection ofinsects, using some South American rainforests as a model; he suggestedover 30 million species (May, 1992) More recently Ehrlich and Wilson (1991)have estimated that living species could reach the 100 million mark! In fact,

in the last few years, “the fondness of God for beetles and in general insects”has been extended for many other taxa such as bacteria, fungi, and manysmall invertebrates like mites and nematodes (Paoletti et al., 1992)

There are at least two points that amaze the researcher: how many tles and insect species we have on the planet and how few plant and animalspecies we currently consider as our possible food In Western countries, forinstance, insects as well as most small invertebrates are still considered ined-ible, in spite of the evidence supporting insects to be the large majority of liv-ing organisms However, over 1500 species of insects are eaten worldwide,especially in tropical and Far Eastern countries (DeFolliart, 1999) In addition,many small, unconventional vertebrates such as reptilians, amphibians, androdents, and invertebrates, such as spiders and earthworms which arereferred to as minilivestock, are also used as food, especially in tropical areas(Paoletti and Bukkens, 1997) Approximately 90% of world food for peoplecomes from just 15 plant and 8 animal species (Wilson, 1988) However, theuse of biodiversity is incredibly different among different human groups InJava, small farmers cultivate 607 crop species in their gardens, with an over-all species diversity comparable to deciduous subtropical forests (Dover andTalbot, 1987; Michon, 1983) In Swaziland, 220 wild plant species are com-monly consumed (Ogle and Grivetti, 1985) Among the Caiçara coastal com-munities of the Atlantic forest, up to 276 plants are used, of which 88 are formedicine (Rossato et al., 1999) Andean farmers cultivate many clones ofpotatoes, more than 1000 of which have names (Clawson, 1985) In northeastItaly (Friuli), an old tradition of wild plant gatherings in spring culminates in

bee-54 different species (Paoletti et al., 1995) Amerindians collect hundreds ofplants and edible animals In most cases, people living in tropical areas have

a better developed attitude toward using a variety of creatures For instance,Martin et al (1987) have cited about 2000 edible perennial fruits in the trop-ics In the tropics as elsewhere, modernization and market economies have inmany cases reduced in practice the number of species and varieties used asfood and medicine, and a strong effort has to be made to reinforce local nativeknowledge about biodiversity and to maintain it into schools and societies.For example, more recent colonizers, such as the Caboclos in the BrazilianAmazon and the Caiçaras in the Atlantic forest have a limited use of insects

as food (respectively three and one species, compared with the Amerindiansliving in the Amazon, such as the Yanomamo Ye’kuana, and Piaroa, who con-sume many different species (Paoletti and Dufour, 2000) Likewise, villagersnear larger cities in the Amazonas, Venezuela, have a limited knowledge of

animals, plants and insects as food compared with villagers farther from thetown.

Maintaining high interest for the diversity of plants, animals, and localuses is the way to maintaining the diversity of natural resources Maintainingand promoting biodiversity means keeping knowledge and local culturesalive However, to manage and consider diversity as a chance for human life,one must consider limits in the human capability to memorize the living crea-tures, and then account for plurality of species

PLURALITY OF SPECIES BIOINDICATORS AND THE HUMAN

LIMITED ABILITY TO MEMORIZE

How can people be made aware of the 600 to 3000 species of brates living in most mixed landscapes in temperate countries or the perhaps

inverte-5000 to 18,000 species in tropical forested landscapes (Paoletti et al., 1992;Hammond, 1992)? As each species has at least several different larval stagesand sometimes exhibits sexual dimorphism and variability in color pattern,the information for each species must be multiplied at least five- to sixfoldand multiplied again if varieties of each species are included

Books, book figures, and taxonomic identification keys are useful but,with some exceptions, are suited only for experienced researchers Openidentification systems afforded by computer programs greatly facilitate thetask of classifying organisms that at first glance are very similar in appear-ance (see the Lombri CD-ROM developed for earthworm identification byPaoletti and Gradenigo, 1996) The new approach to accomplishing the firststep of any biodiversity study is the correct identification of the organismspresent in a system

The aim of bioindicator-based studies is to use the living components ofthe environment under study (especially those with the highest diversity, theinvertebrates) as the key to assess the transformations and effects, and, in thecase of landscape reclamation, to monitor the remediation process in differ-ent parts of the landscape over time This approach could improve policiesaimed at reducing the stress placed on landscapes For example, bioindicator-based studies could help the process of ameliorating and remediating therural landscape as a result of policy implementation, such as the set-aside inEurope (Jordan, 1993; Jorg, 1994) Reductions in agricultural pesticide usecould be adequately monitored by bioindicators to assess the benefit of a newpolicy (Pimentel, 1997; Paoletti, 1999) Bioindicators could also be used toassess and remediate contaminated areas or polluted areas to be reclaimed(Van Straalen and Krivolutsky, 1996)

Such applications of bioindicators can be expected to help not only toimprove the environment but also to augment awareness of the living crea-tures around, so that a better appreciation of the crucial role in sustaining life

on the planet is obtained

WHAT IS BIODIVERSITY AND HOW CAN IT BE USED TO

ASSESS THE LANDSCAPE?

Without biodiversity life on earth would be impossible Based on recentestimates, biodiversity accounts for between 319 billion and 33,000 billiondollars per year in value (Pimentel et al 1997; Costanza et al., 1997) (Table2.2) Biodiversity encompasses all of the species, food-chains, and biologicalpatterns in an environmental system, as small as a microcosm or as large as alandscape or geographic region (Heywood and Watson, 1995; Wilson, 1988;1997) The concept of biodiversity has grown with the perception of its lossincreasing human impact and mismanagement of the environment (Wilson,1988) Whether on a local, regional, or global scale, reduced biotic diversity isassociated with increased environmental stress and reduced environmentalheterogeneity (Erwin, 1996) Biodiversity implies an environment rich in dif-ferent organisms and can be read as a system in which species circulate and

Table 2.2 Total estimated economic benefits of biodiversity in the

United States and worldwide (Modified from Pimentel et al., 1997) Data in billions of U.S dollars.

Bioremediation of chemicals 22.5 121

Livestock breeding (genetics) 20 40

Host plant resistance (forests) 0.8 11 Perennial grains (potential) 17 170

Forests’ sequestering of carbon dioxide 6 135

interact Structure, scale, and features of the landscape also enter into the inition of biodiversity.

def-Although human activities do not invariably work against biodiversity,they can strongly reduce it; for example, in agriculture, productivity of a cropper unit of time and market opportunity almost always make monoculturecropping more profitable and convenient (Odum, 1984; Paoletti et al., 1989;Paoletti and Pimentel, 1992) However, this is not always the case, as demon-strated by the fact that, both in temperate and tropical areas, certain practices

of polyculture and agroforestry or specialized types of agriculture (organic orintegrated farming) can maintain high biodiversity while at the same timeproducing adequate returns for farmers (Altieri, 1999; DeJong, 1997; Paoletti

et al., 1993) It has also been observed that some urban areas support greaternumbers of species (such as of birds) than the surrounding rural landscapedominated by monocultures and landscape simplification under high input(Paoletti and Pimentel, 1992)

Careful analysis of apparently “unmanaged” primary rain forests strates that, in addition to being manipulated by their “original” components,they are sometimes strongly influenced by human activities as well The well-studied case of the relationship between the Kayapo Indians and their envi-ronment in the Brazilian Amazon (Posey, 1992) may have many similar,unstudied equivalents, e.g., the Yanomamo, Piaroa, Curripaco, and MakiritareIndians (living in the Alto Orinoco, Amazonas,Venezuela) The Makiritarehave been observed actively disseminating their favored edible white benthic

demon-earthworms (motto) on the beaches of affluents of the Padamo river Likewise,

the hedgerows found in many European landscapes (in some cases ing with the Ancient Roman centuriations; Paoletti, 1985) and the terracingused in Mediterranean agriculture are associated with increased numbers ofspecies and landscape diversity (Paoletti and Pimentel, 1992) In Liguria,Italy, the pre-bugium, for instance, is a mixture of several edible wild herbscollected especially on walls adopted to terrace the steep rural landscape

originat-WHAT BIOINDICATORS ARE AND HOW TO USE THEM

The concept of bioindicators is a trivial simplification of what probablyhappens in nature It can be defined as a species or assemblage of species that

is particulary well matched to specific features of the landscape and/or thatreacts to impacts and changes (Paoletti and Bressan, 1996; VanStraalen, 1997).Examples of bioindicators are species that cannot normally live outside theforest, that live only in grasslands or in cultivated land, that support high lev-els of pollutants in their body tissues, that react to a particular soil manage-ment practice, and that support waterlogging Bioindication is not a newterm; it has evolved from geobotany and environmental studies from the lastcentury (Paoletti et al., 1991) It has become an important paradigm in theprocess of assessing damaged and contaminated areas, monocultures,

different input farming, different tillage systems, contaminated orchards,disposal areas, industrial and urban settlements, and areas neighboringpower plants.

In empirical terms a bioindicator can be thought of as a label for a ular situation and environmental condition However, this is a very simplis-tic view Although the identification of a species as a label for a particularenvironment can be convincing, rapid changes in landscape use, especially inthe mosaic situation, can reduce the bioindicative value of a particularspecies All species react to environmental changes and can adopt new pat-terns and behavior to cope with the change; the many pest species that haveevolved from wild, nonpest species is an obvious example of this phenome-non Evolutionary mechanisms involving species are not absent in the man-aged area The disappearance of a single species from a landscape can betraced from either a complex combination of events, including the collapse ofmetapopulations as affected by reduction of connectivity (e.g., margins,lanes, hedgerows, riverbanks), or to a single major event, such as field dimen-sion, tillage, or field contamination (Burel, 1992)

partic-Instead of focusing on a few indicator species, more reliable informationcan be gained from studies of a set of species or a higher taxon, with meas-urements made not at the level of presence/absence but as numbers, bio-mass, and dominance The use of guilds such as detritivores, predators,pollinators, parasitoids, dung decomposers, and carrion scavengers asbioindicators can reveal interesting differences in the landscape

Patterns of herbivory in polluted areas, e.g., the abundance of aphids ontrees or mining lepidoptera, have been correlated with industrial pollutionand in particular with increased levels of available nutrients (free aminoacids) in the stressed trees (Holopainen and Oksanen, 1995) A study inDenmark showed that the complex of parasitoid Hymenoptera (up to 164species) living in cereal field soils can accurately discriminate between fieldsthat have been spread with the currently used pesticides and untreated fields(Jensen, 1997) The importance of fungivores in detecting cereal fields withand without pesticide (fungicide) inputs has also been shown (Redderson,1995) For example, the detritivores were demonstrated to be a fine way todiscriminate organic apple orchards from conventional apple orchards(Paoletti et al., 1995)

WHAT IS SUSTAINABILITY?

Table 2.3 shows the potential meaning and the current use of the term

sustainability, focusing on the aspect of stability over time In terms of the

environment, sustainability signifies maintaining the productivity andpotential of an ecosystem used by humans with time This theoretical situa-tion normally never happens in practice (Conway and Barbier, 1990; Altieri,1995) As discussed by Carter and Dale (1974) and Ponting (1991), most

Table 2.3 Comparison of social, economic, and environmental sustainability

(Modified from different sources, especially the work of Goodland and Pimentel, 1998).

Sustainability Sustainability Sustainability

Although ES is needed by humans and originated because of social concerns, ES itself seeks

to improve human welfare

by protecting the sources

of raw materials used for human needs, and ensuring that the sinks for human wastes are not exceeded, in order to prevent harm to humans Humanity must learn to live within the limitations

of the biophysical environment ES signifies that natural capital must

be maintained, both as a provider of inputs of sources and as a sink for wastes This requires that the scale of the human economic subsystem be held to within the biophysical limits of the overall ecosystem on which it depends ES needs sustainable consumption by a stable population.

On the sink side, this translates into holding waste emissions within the assimilative capacity

of the environment without impairing it.

On the source side, harvest rates of renewables must be kept within regeneration rates.

Economic capital should

be stable The widely accepted definition of economic sustainability is

maintenance of capital,

or keeping capital intact.

The amount consumed in

a period must maintain the capital intact because only the interest rather than capital has to be consumed.

Economics has rarely been concerned with natural capital (e.g., intact forests, healthy air, stable soil fertility) To the traditional economic criteria of allocation and efficiency must now be added a third, that of scale The scale criterion would constrain

throughput growth—the flow of material and energy (natural capital) from environmental sources to sinks.

Economic values are restricted to money;

valuing the natural intergenerational capital, such as soil, water, air, biodiversity, is

laws, discipline, etc.

constitute the aspects

of social capital least

shared values and

equal rights, and by

civilizations have in the past collapsed and disappeared, as in ecological cessions, because of the destruction of natural resources, especially soil andits organic components The few cases in which fertility has been maintainedfor long periods (more than 800–2000 years) always involved active input ofhumus, such as the regular replenishment of carbon and nutrients in the NileValley of Egypt by flooding of the Nile River By changing the temporal scale,civilizations that disappeared because of mismanagement of resources can belooked upon as a succession inside the ecosystem (Golley, 1977) Humanintervention in the landscape almost always has a strong impact onresources, which become depleted or degraded in their potentialities and aresoon substituted with artificial ones that are more energy intensive (e.g.,organic compounds in agroecosystems substituted by chemical fertilizersand pesticides) Loss of diversity and species is practically guaranteed inmost agricultural systems (Paoletti, 1985; Naem et al., 1994; Tilman et al.,1996) Increasing the cost of crops in terms of energy by adopting moderntechnologies is a trend documented in an array of situations worldwide(Pimentel and Pimentel, 1996) Although the trend toward reduced biodiver-sity in managed environments continues to worsen, systems for sustainableuse of natural resources exist and are growing in number For example, in thetropics, government policies aimed at setting up villages for farmers who are

suc-accustomed to slash and burn practices in the forest tend to result in

savan-naization This process occurs because, instead of being allowed to choose

fresh plots, the farmers are restricted to reusing forest plots near their lages, which consequently have limited fallow periods between plantings(Lopez Hernandez et al., 1997; Netuzhilin et al., 2000) The savannaizationprocess is apparently less severe when the farmers have access to more forestarea (Kleinman et al., 1995)

vil-With sustainability, reduction of external inputs and improved ment of species improve diversity of the system while at the same time main-taining a constant level of productivity This process requires sophisticatedknowledge of the resources For example, some groups of Amerindians liv-ing in tropical rain forests are able to manage over 1400 different species ofplants and animals (Table 2.1) Without a strong educational system, theknowledge involved in these practices would be lost from the group and theforest would no longer be optimally managed Paradoxically, introduction offormal schools can reduce propagation of this traditional local knowledge inthe extended family groups, thereby rendering the younger generationsunable to live in the forest in a sustainable manner

manage-Sustainability of a given unit (farm, factory, urbanized area, complex scape) can be assessed only by comparison with other similar units that areunder different management Although it is difficult to assign absolute val-ues of sustainability to a given landscape, comparisons with other landscapescan indicate promising, compatible practices (Paoletti and Bressan, 1996).When developing an assessment program, it is useful to have a substan-tial number of cases in order to aid understanding the situation and to make

land-a finland-al judgment regland-arding the best choice of mland-anland-agement prland-actices to bepromoted Environmental sustainability must match economical viability,social acceptance, and long term equitability (Conway and Barbier, 1990) Inaddition to well-thought-out general policies to prevent inappropriate envi-ronmental stresses (Goodland and Pimentel, 1998), improved sustainability

of landscapes requires education of citizens, farmers, and policy makers Inany case, bioindicators, the small organisms of a given habitat, represent thepractical tools to assess comparatively the sustainability of a farm, a piece oflandscape, or a reclaimed area (Table 2.4)

LANDSCAPE vs LANDSCAPE STRUCTURE

A landscape is a complex and large-scale system, river basin, region, etc.,

in which different ecosystems, soils, species, animal and plant guilds, logical cycles, and human activities are associated with each other In ruralareas, different farms can adopt different crops, some-times changing styles

eco-of farming over time and space (Aebischer, 1990; Paoletti et al., 1993, Paoletti

et al., 1997) In urban and industrialized areas, cycles of production, ment and waste disposal are the key elements that determine the profile of alandscape In both rural and urban-industrialized landscapes, the strategy ofwaste disposal is the most important factor affecting the environment.Species distribution and abundance are affected by the landscape mosaicstructure, the presence and fragmentation of margins, and management ofdifferent parts of the agroecosystems contained in the landscape Comparingdifferent landscape units such as farms, fields, and plots is the matter ofbioindicators To make the comparison and improve management for envi-ronmental sustainability, three steps are needed: define the unit to be com-pared, make a preliminary assessment, and implement the appropriatedesign of sampling and kind of indicators to adopt Selecting the less dis-turbed units within the landscape under examination is important becausethey could be the local references considered as a control

manage-MARGIN EFFECTS (HEDGEROWS, SHELTERBELTS, WEED

STRIPS)

Trees organized in rows, shelterbelts, and patches of bushes, vines, andherbs are a constant component of traditional farming landscapes in manytropical and temperate countries Weedy margins (sometimes used as pathsfor machinery), ditches, fences, walls, and enclosures all create margins.These structures, in particular hedgerows and shelterbelts, serve many pur-poses, including providing a source of wood for burning and building, secur-ing emergence fodder, providing a microclimate, and improving diversityand connectivity in the landscape (Joenie et al., 1997) In many cases, these

microhabitats represent important refuges for beneficial predators and sitoids (Nazzi et al., 1989; Paoletti and Lorenzoni,1989; Paoletti et al., 1997;Sommaggio et al., 1995) It is not clear whether such wild vegetation patchescan also enhance the activities of pests in the rural landscape The hosting

para-of some pests (e.g., aphids and spidermites) is compensated for by the factthat margins can also support polyphagous predators as well, providing

Table 2.4 Farming systems that can augment biodiversity in agroecosystems

(Modified from Paoletti et Sommaggio, 1996; Paoletti, 1999 modified) Sustained Invertebrate Biodiversity Decreased Biodiversity

rotation with legumes 10

monosuccession dead mulch, living mulch 7,10 bare soil

herbal strip inside crops 18,19

homogeneous fields appropriate field margins 17 large fields

small fields surrounded by woodland 11

large fields hedgerow surrounded fields 20 open fields

ribbon cropping* conventional cropping

living trees sustaining grapes* artificial stakes

minimum, no tillage, ridge tillage 7,16 conventional plowing

mosaic landscape structure 8,9,15

landscape simplification, woodland clearance

organic sustainable farming 5,10

intensive input farming

on farm research 13,14 conventional plot research

organic fertilizer 5,10

chemical fertilizer biological pest control 6 conventional chemical pest control plant resistance 6,21

plant susceptibility germoplasm diversity 1,2 standardization on a few cultivars nontransgenes 22

engineered, transgenic crops solarization of soil 23 using herbicides-fungicides

1 Altieri et al., 1987 13 Stinner et al., 1991

2 Lal, 1989 14 Lockeretz, 1987

3 Oldfield and Alcorni, 1987 15 Karg, 1989

5 Matthey et al., 1990 16 Exner et al., 1990

6 Pimentel et al., 1991 17 Paoletti et al., 1997a

7 Stinner and House, 1990 18 Joenie et al., 1997

8 Paoletti, 1988 19 Lys and Nentwig, 1992,1994

9 Noss, 1990 20 Nazzi et al., 1989

10 Werner and Dindal, 1990 21 Pingali and Roger, 1995

11 Paoletti et al., 1989 22 McCullum et al., 1998

12 Favretto et al., 1991 23 Ghini et al., 1993

*unpublished assessments (Paoletti 1987 –1990)

overwintering sites which allow them to predate effectively early in the son (Paoletti and Lorenzoni, 1989; Paoletti et al., 1997) These less-managedareas (hedgerows, strip weed margins) can also support a higher diversity ofsoil fauna (including more earthworms and carabids; unpublished data),accompanied by increased microorganism activity (microbial nitrogen andphosphorus) (Figure 2.1a/b/c).

sea-Peculiar “beetles banks” and managed field margins seeded with mixedgrasses and leguminous plants have been shown to be important habitats forpolyphagous predators such as carabids, spiders, and other invertebrates,over the season and are also good refuges for overwintering In addition,these strips or margins can help in disseminating beneficial invertebrates intocultivated fields (Joenie et al., 1997; Carli, 1997; Lys and Nentwig, 1992, 1994;Lys et al., 1994; Frank and Nentwig, 1995; Paoletti and Lorenzoni, 1989)

CORRIDORS AND CONNECTIVITY IN THE LANDSCAPE

When forested landscape is transformed and managed, the natural etation removed and substituted with crops, movements of small organismsbecome more problematic; this problem can in part be overcome by the pres-ence of elements such as hedgerows, channels, banks, paths, path margins,and road margins that provide a continuum in space (Burel and Baudry, 1990;Joenie et al., 1997) Connectivity is the property that spatially links differentparts of a landscape Biota, especially small animals but also plants, can beintensively affected by this feature of the landscape (Yu et al., 1998) In addi-tion, hedgerows, roads, and rivers can contain metapopulations Figure 2.2,which illustrates a study of recaptured carabids carried out in England,demonstrates the border effect of hedges making, to some extent, the fieldspermeable to free movements

veg-EFFECT OF MOSAICS IN THE LANDSCAPE

Plurality of patterns, margins, and different plant-crop units into a

land-scape confers patchiness, the mosaic effect that can be measured and be

related to animal biota (abundance and distribution) In rural landscapes, thepattern of different soil uses within a farm can confer a peculiar mosaic char-acter to the area Different farming systems affect the rural landscape and thebiota living in the area Particular styles of farming (rotation instead of mono-culture, perennial crops instead of annuals, contour tillage, minimum tillage,etc.) can change the mosaic character of a given area Rotation instead ofmonoculture offers a different level of patchiness to the landscape Riverbanks, ditch slopes, and grassy margins can represent important elements forcolonization organisms in the landscape The layout of the fields (dimensionand shape) can also affect movements and colonization patterns of herbi-vores and predators (Paoletti and Lorenzoni, 1989; Sommaggio et al., 1995)

Figure 2.1a/b/c A Nitrogen microbial biomass is in general more abundant in an

alfalfa margin near the hedgerow than in the center of the alfalfa field.

In addition, B detritivores and in many cases C predators fauna sorted with modified Tullgren) are more abundant near the hedgerows than in the center of the alfalfa field Survey carried out in

(micro-Po Valley, province of Venice (Modified from Ottaviani, 1992, in Paoletti, 1999).

COLONIZATION AND RECOLONIZATION DYNAMICS AND

PENDULARISM

Field margins, shelterbelts, and different patches of the rural scape can assume the function of continent, and fields can assume the func-tion of islands to be recolonized from animals and seeds It is not always easy

land-to demonstrate this movement and effectively track these strategies Tounderstand the landscape and assess bioindicators, it is important to beaware of the movements and strategies of living biota

Hedgerow Isolated

An old hedgerow or a field margin in the simplified rural landscapedominated by monocultures can be the reference continent in a simplifiedsystem dominated for instance by corn, soybean, sugar beet or winter cerals.The complex hedgerow can host and affect several invertebrates includingpredators and parasitoids that early in spring move in the surrounding crops.When the crop becomes dry or is harvested, and fields are tilled, the inverte-brate component can find shelter back in the hedgerow or field margin(Paoletti, 1984; Paoletti and Lorenzoni, 1989; Paoletti et al 1997a; Figure 2.3).Wood remnants and shelterbelts (sufficiently diverse in vegetation) canact for the surrounding fields the same role of islands that are recolonized bythe continent However, at the end of the season fields can be highly dense ininvertebrate populations that in a pendular mechanism recolonize their “con-tinent.” Then predators and parasitoids that can find shelter and overwinter

in such “continents” will be better fitted to stay in the landscape (Figure 2.4)

Figure 2.1a/b/c (Continued)

Figure 2.2 A Pitfall recapturing experiments show that hedgerows can affect the

free circulation of the soil-moving polyphagous carabid Pterostichus

melanarius (near Bristol, England) B The second figure documents that

hedgerows in summer attract a typical field ground beetle, Harpalus

rufipes (near Bristol, England).