Traditional Agroecosystems Research Articles

Genetic Diversity of Traditional South American Landraces of Cassava (Manihot Esculenta Crantz): An Analysis Using Microsatellites

The extent and structure of the genetic variability of traditional varieties of cassava (Manihot esculenta Crantz) have been little documented, despite considerable evidence for this cropś great varietal diversity in traditional agroecosystems. We used microsatellite markers to assess the genetic structure of traditional landraces of sweet and bitter cassava collected from five South American sites. As reference, we used a sample of 38 accessions from a world collection of cultivated cassava. For a total of 10 loci examined, we found 15 alleles that were not represented in this sample. Ten of these had been previously detected in wild Manihot species. The geographical structure of genetic variability was weak, but the genetic differentiation between bitter and sweet landraces was significant, suggesting that each form had evolved separately after domestication. Our results showed that traditional landraces form an important source of genetic diversity and merit more attention from managers of crop genetic resources.

Traditional Agriculture and the Conservation of Biological Diversity in Crete, Greece

The biological diversity in traditional agroecosystems and potential diversity loss associated with land use change in upland Crete was investigated. Using transects, plots and point count sampling methods, the dominant vegetation types and land uses, floristic diversity, breeding birds, and key biophysical attributes of remnant traditional agroecosystems in three upland catchments were identified. Eight vegetation/land use types were observed, including: chestnut stands, old olive groves, maquis, phrygana, intensively cropped parcels, rock walls and hedges, woodlands, and intensive olive groves. Eighty-three native plant species in traditional agroecosystems were recorded, the majority of which were shade intolerant perennial herbs and shrubs adapted to grazing and browsing. The vegetation types/land uses were distributed in a complex mosaic across the landscape, exhibited a wide range of light conditions, structural attributes, percent ground cover, soil organic matter levels, and provided breeding habitat for at least 19 bird species. Traditional farming, grazing and forestry are declining throughout the northern Mediterranean. Woodlands and intensive olive monocultures have replaced diverse land use mosaics and contain less biological diversity than traditional agroecoystems. The conservation of Mediterranean floristic diversity necessitates understanding disturbance regimes and may require maintaining the land use practices and mosaics associated with traditional cultivation practices and livestock grazing.

Ecophysiology of Dominant Plant Species during Old-Field Succession in a High Tropical Andean Ecosystem

We compared ecophysiological characteristics of plant species that dominate during different stages of succession in fallow fields of a traditional agroecosystem in the Venezuelan High Andes. For each species we determined during the dry and wet seasons the photosynthetic light response and photosynthesis rate at light saturation (Amax), specific leaf area (SLA), stomatal conductance at light saturation (gmax), midday water potential (ψ), and intrinsic water use efficiency (WUEi, photosynthesis rate per unit of stomatal conductance). The species studied were the forbs Rumex acetosella (early succession dominant) and Lupinus meridanus (intermediate stages), the shrubs Acaena elongata and Baccharis prunifolìa (late succession), the giant rosette Espeletia schultzii, and the shrub Hypericum laricifolium (mature ecosystem dominant). Clear ecophysiological trends were identified: early and intermediate successional species had higher Amax, gmax, and SLA but lower WUEi. E. schultzii maintained a high water potential during the dry season and, together with B. prunifolia, was the only species with no significant differences in Amax between seasons. The results indicate that traits generally linked to fast growth (high Amax and SLA) are associated with dominance during early succession, while traits linked with drought resistance (e.g., high WUEi and thick xeromorphic leaves) are associated with dominance during late succession in this tropical mountain environment.

Strategies for agrobiodiversity conservation and promotion: a case from Yunnan, China

This paper deals with strategies for agrobiodiversity conservation and promotion based on studies on four plant groups (selected from 50 plant groups) occurring in the Yunnan Province of China. These plants are edible konjac (Amorphophallus), medicinal Paris, Musella lasiocarpa and wild tea (Camellia sinensis and its wild relatives), including their cultivars and wild populations. After analyzing the target plants, we conclude that the following strategies should be adopted to conserve and promote agrobiodiversity: (1) in situ conservation of agrobiodiversity, including habitat protection of wild populations, maintenance of native species and varieties in traditional agroecosystems, and relevant environmental education; (2) ex situ conservation and promotion of agrobiodiversity, including establishment of living collections and germplasm banks, and introduction of species and varieties into agroecosystems for agricultural practice; and (3) promotion and conservation of agrobiodiversity through sustainable uses, including technique development of propagation, cultivation, pest and disease control, on farm and off farm management, and other activities such as new variety breeding and scientific studies. Strategies developed here will be helpful to conserve and promote agrobiodiversity at agroecosystem, species, variety or landrace, and management system levels.

Germination Ecology of Cassava (Manihot Esculenta Crantz, Euphorbiaceae) in Traditional Agroecosystems: Seed and Seedling Biology of a Vegetatively Propagated Domesticated Plant1

Cassava is clonally propagated, but Amerindian farmers also use plants from volunteer seedlings to prepare stem cuttings. Although sexual reproduction plays a role in cassava’s evolution it is poorly studied. We examined one aspect of cassava reproductive ecology, seed dormancy and germination. Volunteer seedlings emerge from a soil bank of seeds produced during the previous cycle of cultivation that remain ungerminated through the fallow period, then germinate synchronously after vegetation is slashed and burned. Laboratory experiments showed that germination can be enhanced by mechanical scarification and also by dry heat treatment, suggesting that burning after field clearing could help break dormancy. Germination was also stimulated by high temperatures (35°C) that in nature indicate bare soils, and inhibited by temperatures (25°C) close to those in soil shaded by vegetation and by light. Seeds of both wild and domesticated cassava exhibit physiological dormancy, an adaptation for germination in periodically disturbed habitats. In addition to these preadaptations, preliminary results also suggest specific adaptations of domesticated cassava to the distinctive disturbance regimes of swidden agriculture.

Genetic structure and indirect estimates of gene flow in three taxa of Cucurbita (Cucurbitaceae) in western Mexico

Cultivated squash (Cucurbita argyrosperma ssp. argyrosperma and C. moschata) are important in the Mexican traditional agroecosystem. They are typically cultivated within maize fields where adjacent populations of a wild, close relative, C. argyrosperma ssp. sororia, occur. Consequently, there are ample opportunities for gene flow between domesticated and free-living Cucurbita populations. We used allozymes to examine genetic variation and gene flow among these three Cucurbita taxa in the state of Jalisco in Western Mexico. Twelve polymorphic allozyme loci were used to calculate genetic diversity for 16 populations of Cucurbita. We found high levels of genetic variation: polymorphism of 0.96, mean allelic diversity of 2.08, average expected heterozygosity 0.407, and little differentiation among conspecific populations (D = 0.081; F(ST) = 0.087; N(e)m = 5.22). These findings indicate that Cucurbita possess a high pollen dispersal potential, a somewhat surprising result considering they have specialist pollinators. Unweighted pair group method with arithmetic means (UPGMA) analysis of allozymes suggests the existence of at least two distinct groups of populations, one consisting of both subspecies of C. argyrosperma and another consisting of C. moschata.

Studies on hill agro-ecosystems of three tribal villages on the Eastern Ghats of Orissa, India

The sustainable indigenous agro-ecosystems of India, a majority of which are degraded or destroyed, need protection. The main objective of this study was to analyse the traditional agro-ecosystems from structural and functional point of view and their interactions with other biophysical and socio-economic characters with a view to offer possible solutions. Analysis of traditional agro-ecosystems of three tribal villages, inhabited by Kondhs of Eastern Ghats of Orissa, India, revealed that cultivated land occupied 66% of the total land area. This covered valley, shifting and home garden cultivation. Under valley, rice ( Oryza sativa L .) showed the maximum productivity (2–4 Mg ha −1) among the crops. Minor millets and redgram ( Cajanus cajan (L.) Millsp.) were cultivated under shifting cultivation in one of the villages. Vegetables and spices were the main crop under home garden. In valley agriculture human and draught power were the major inputs of energy, while in shifting cultivation human labour was the only source. Out of the total agricultural yield, 52.5, 90.6 and 75.9% were consumed in the villages of Rajikakhola, Nediguda and Badruguda, respectively. When agriculture, forest and animal husbandry sectors were taken together the average share of agricultural sector to the total consumption in the villages was 68.4%, the rest being contributed by forest, while the contribution of animal husbandry was almost negligible. Agricultural production can be stabilized through available rain water management, application of organic manure to agricultural fields and protection of the existing forests. Abandoned Podu (i.e. shifting cultivation) fields can be improved through agro-forestry practices.

Interdisciplinary analysis of homegardens in Nicaragua: micro- zonation, plant use and socioeconomic importance

The choice of plant species, their arrangement and management varies between and within tropical homegardens in the same community. Relationships between agroecological and socioeconomic characteristics of 20 homegardens were examined at Masaya, Nicaragua. Variables analyzed were micro-zonation (area allocation to specific uses and management), plant use and diversity, occupation, labor investment, and product, benefit and income generation. Data was collected through surveys, participatory mapping, plant inventories, direct observation and interviews. Ten different micro-zones and nine plant uses were identified. Fruit trees, shaded coffee and ornamentals were the most important zones. Plant diversity was high, with a sample total of 324 species. Homegardens were an important occupation, with average labor investments of 32.6 h family−1 week−1. Families obtained at least 40 different plant products from homegardens, as well as the benefit of space for working and socializing. Six homegarden types were identified using a cluster analysis based on biophysical variables. Types reflected the relationship between income generation and the number and types of zones and plant species present. Labor inputs were high considering the small size of the homegardens (average size 3,240 m2), although no clear relationships between labor investment and plant and zone type or number were observed. Homegarden management strategies of plant selection and zonation were affected both by family choices and external forces. Although dependence on homegardens may vary according to specific conditions at a given time, they seem to be a consistent, flexible resource used to meet a diversity of needs. The methodological approach used in this paper may be appropriate for the study of other traditional agroecosystems since it includes both biophysical and socioeconomic variables, essential for understanding these complex systems.

Changing scenario of Himalayan agroecosystems: loss of agrobiodiversity, an indicator of environmental change in Central Himalaya, India

Environmental, biological, socio-cultural and economic variations in the Himalayas have led to the evolution of diverse and unique traditional agroecosystems, crop species, and livestock, which help the traditional mountain farming societies to sustain themselves. During the recent past, as a result of rapid changes in land use caused by socio-cultural and economic changes and various environmental perturbations, the agrobiodiversity of the Central Himalayan agroecosystems has changed steadily. A recent survey conducted in 150 different villages located along an elevated transect of the Alaknanda catchment of the Central Himalaya revealed that over a period of two decades (1970–74 and 1990–94) the cultivated area under many traditional crops had declined significantly. A micro-level study carried out in 30 villages revealed that a series of changes had occurred in land use practices over a period of 25–30 years. The loss of agrobiodiversity and the changing socio-cultural and economic dimensions and their impacts on the sustainability of Himalayan agroecosystems are emerging as major causes of concern at local/regional/national scale, and appropriate options to meet these challenges are discussed in this paper.

The unmanaged reproductive ecology of domesticated plants in traditional agroecosystems: An example involving cassavaand a call for data

Abstract Although cassava is a strictly vegetatively propagated crop, in many traditional Amazonian agroecosystems, Amerindian farmers recognise volunteer seedlings of cassava and allow them to grow. If their properties are deemed desirable, plants originating from seedlings are included in the harvest of tuberous roots, and their stems are used to prepare cuttings for propagation. Incorporation of these products of spontaneous sexual reproduction appears to be important in origin and maintenance of genetic diversity in this clonally propagated plant. Our observations conducted in an Amerindian village in Guyana suggest that volunteer seedlings arise from a bank of viable seeds stored in soil, and that dispersal and burial of seeds by ants may be important in its constitution. Future investigations of the dynamics of genetic diversity in this crop in traditional agroecosystems must consider the role of the ‘wild’ sexual reproduction that occurs in parallel with vegetative propagation. We suggest that unmanaged processes of sexual reproduction play important but neglected roles in the evolutionary ecology of many domesticated plants in traditional agroecosystems.

Multifunctional dimensions of ecologically-based agriculture in Latin America

SUMMARY Today in Latin America there are still regions with microcosms of traditional farming systems, (i.e. in Mesoamerica, the Andean region, and the Amazon Basin) that have emerged over centuries of cultural and biological evolution. These are based on locally available resources and the cultivation of a diversity of crops and varieties in time and space, and have allowed traditional farmers to maximize harvest security and the multiple use of the landscape with limited environmental impact. Agro-biodiverse traditional agroecosystems represent a strategy which ensures diverse diets and income sources, stable production, minimum risk, efficient use of land resources, and enhanced ecological integrity. This legacy of traditional agriculture demonstrates that the combination of stable and diverse production, internally generated and maintainable inputs, favourable energy input/output ratios, and articulation with both subsistence and market needs, comprises an effective approach to achieve food security, income generation, and environmental conservation. Traditional approaches represent multiple use strategies that enhance the multifunctional nature of agriculture, an important feature for the health of rural regions in the next century.

Allelopathy as a Tool in the Management of Biotic Resources in Agroecosystems

In modern agriculture, natural plant communities may be replaced by a single crop species. Weeds, some microorganisms, and viruses, as well as some herbivores are organisms that should be eliminated. Pesticides and fertilizers not only affect the pests and crops, but soil, non-pest species, water, food, and humans. In traditional agriculture weeds are components with an important ecological role in the maintenance of the system. Some weeds have been used as tools to control the growth of other weeds in traditional agroecosystems. Researchers on sustainable and organic agriculture get valuable information from traditional agriculture and currently are conducting research on plant breeding, soil fertility and tillage, crop protection, and cropping systems. Allelopathy and chemical ecology are directly involved in each of these fields and can play an important role in crop productivity, conservation of genetic diversity, and maintenance of ecosystems stability. Allelopathy has been shown to be related with problems of chemical interference between crops and weeds, crops and crops, toxicity of crops and weeds residues, and/or crops and weeds exudates. Problems of autotoxicity, orchard replanting, and forest regeneration are also referred as allelopathic. Allelopathy is strongly coupled with other stresses of the environment, including insects and disease, temperature extremes, nutrient and moisture variables, radiation, and herbicides. These stress conditions often enhance allelochemical production and increase the potential for allelopathic interference. Allelopathy offers potential for weed control through the production and release of allelochemicals from plants. Allelochemicals may impact the availability of nutrients through effects on the symbiotic microbes. Destruction and changes in the use of soils in the tropics have decreased biodiversity, bringing about the loss of valuable natural products. Many different types of useful products such as natural pesticides and drugs can arise from allelopathy studies. New methods must be generated for allelopathy as a part of the biotic resources management strategies.

Some recent issues on the conservation of crop genetic resources in developing countries

Crop genetic resources (CGRs) are renewable resources. These resources are enriched rather than depleted by their use in research and plant breeding. Both at the time of Vavilov and, later, in the early 1970s, when concerted international efforts to collect and preserve CGRs started with the initiatives of the International Board for Plant Genetic Resources (IBPGR), CGRs were considered to be the common heritage of humankind. Now, they are widely accepted as "national heritage." Possible impacts of this nationalization on the utilization and enrichment of global crop genetic diversity and, consequently, on global food security are issues of great significance. At present, efficient management and adequate use of CGRs are more important concerns than their further exploration and collection. To increase the use of preserved CGRs in plant breeding, the formation of core collections, by selecting representative subsets from large ex situ collections of CGRs, was recommended in 1984. Since then, the core-collection strategy has been further justified as a practical approach to genetic resources management, as well as to their conservation. As a cost-saving germplasm-management strategy, the core-collection concept has considerable merit. However, the rapidly increasing popularity of core collections may undermine the genetic wealth stored in national gene banks of both developed and developing countries. Distinction is made between subsets of working collections and core collections. When a small number of CGRs is required for specific plant breeding purposes, a properly formed working collection is more useful than a representative collection. Despite the relative abundance of genetic diversity in crop plants in traditional agroecosystems, maintenance of these agroecosystems is not a realistic long-term alternative for preserving crop genetic diversity and ensuring global food security. What is needed in the "gene-rich" developing countries is the adoption of "biodiversity friendly" plant breeding and agricultural practices.Key words: crop genetic resources, core collection, germplasm conservation, in situ conservation, ex situ conservation, modern landraces.

Conservation in Brazil's Chocolate Forest: The Unlikely Persistence of the Traditional Cocoa Agroecosystem.

/ In southern Bahia, Brazil, the traditional cocoa agroecosystem with a dense shade canopy of native trees is now recognized as a secondary conservation route for highly endangered Atlantic Rainforest species. This "chocolate forest" of the densely shaded farms persists despite a massive 20-year Brazilian government modernization program in which shade was seen as a chief impediment to raising cocoa production. The objective of this study was to determine how this traditional agroecosystem endured. Although dense shade limits cocoa yield, it provides several agroecological benefits: control of insect pests and weeds, microclimate stability, and soil fertility maintenance. A keycomponent of modernization efforts was a shade-tree removal program designed to maximize cocoa production by using low shade and fertilizer while substituting agrochemicals for many beneficial roles of the overhead trees. This research found that many farmers rejected, or only partially accepted, the shade reduction process although it promised much higher cocoa yield and profit. Farmers employing a wide range of shading were interviewed, and it was found that decisions to remove or maintain the shade trees were linked to both agroecological and risk-minimization factors. Farmers' perceptions of the agroecological functions of the shade trees and individual willingness to entertain the economic risk associated with substituting agrochemicals for these were important. A less-profitable, but lower-risk approach of occasional fertilizer and agrochemical use with the traditional shade intact was a rational and widespread choice. Policies designed to maintain the traditional agroecosystem through the current economic crisis should heed the multiple functions of the overhead trees. KEY WORDS: Conservation; Brazil; Atlantic Rainforest; Cocoa; Agroecology; Risk; Agroforestry

Arthropod biodiversity loss and the transformation of a tropical agro-ecosystem

The coffee (Coffea arabica) agro-ecosystem in the Central Valley of Costa Rica was formerly characterized by a high vegetational diversity. This complex system has been undergoing a major transformation to capital-intensive monocultural plantations where all shade trees are eliminated. In this study we examined the pattern of arthropod biodiversity loss associated with this transformation. Canopy arthropods were sampled in three coffee farms: a traditional plantation with many species of shade trees, a moderately shaded plantation with only Erythrina poeppigeana and coffee, and a coffee monoculture. An insecticidal fogging technique was used to sample both canopy and coffee arthropods. Data are presented on three major taxonomic groups: Coleoptera, non-formicid Hymenoptera, and Formicidae. Data demonstrate that the transformation of the coffee agro-ecosystem results in a significant loss of biological diversity of both canopy arthropods as well as arthropods living in coffee bushes. Percentage of species overlap was very small for all comparisons. Furthermore, species' richness on a per tree basis was found to be within the same order of magnitude as that reported for trees in tropical forests. If results presented here are generalizable, this means that conservation efforts to preserve biological diversity should also include traditional agro-ecosystems as conservation units.

Traditional crop diversity for sustainable development of Central Himalayan agroecosystems

SUMMARY A rich diversity of traditional crops occurs generally in the Himalaya and more particularly in Central Himalaya. Over forty species of food grains are grown in traditional agroecosystems of Central Himalaya, which have been managed by the local farming communities since time immemorial. These traditional crop varieties have evolved over centuries and are well adapted to the particular area. A number of edaphic, topographic and climatic factors associated with different selection pressures over centuries of cultivation resulted in immense variations in the crop species. The grain and by-product yield of the majority of the traditional crops cultivated across an altitudinal gradient were worked out and compared with common food crops (paddy, wheat, mustard) at two points in time (1970-74, 1990–94) and it was found that almost all the traditional crops had slightly higher yields during 1970–74 than between 1990–94. However, common food crops grown during the Kharif season had higher yields during 1990–94 whereas, Rabi season crops exhibited higher yield during 1970–74. The yield of rainfed paddy remained static over the years across the altitudinal gradient. Among the traditional crops cultivated during the Kharif and Rabi seasons in mixed and pure forms at different altitudes were Macrotyloma uniforum (at higher altitude), Parilla frutescens and Vigna mungo (at middle altitude) and Panicum miliaceum (at lower altitude) which were found to be eco-energetically efficient. Avena sativa (oat) and mixed cropping of Fagopyrum esculentum and potato had higher energy efficiency ratios whereas the latter also exhibited a higher monetary output/input ratio. Crops like paddy and wheat with mustard, grown in irrigated land were found to be more eco-energetically efficient than the same crops grown in the rainfed land. In general, traditional crops possess higher nutritive value than the common food crops. The contribution of traditional crops to the local diet (kg/capita/year) and their energy and protein equivalents were higher during both time periods. It was observed that while exporting these traditional crops, the locals of the region are highly exploited by middlemen. Despite having huge potential, traditional crop diversity of this region has been reduced to a great extent during the last two decades. Besides, the area under cultivation with these crops has been declining rapidly. However, many of these crops possess immense potential to meet the growing food demand and ensure food security of an increasing population. Therefore, a comprehensive programme of conservation through various means and improvement of agronomic yield in their natural habitats is urgently needed.

The supply of phosphorus from native, inorganic phosphorus pools in continuously cultivated Mexican agroecosystems

Correlative and experimental approaches were used to determine the sources of phosphorus (P) that supply the labile P pools in nine soils from traditional Mexican agroecosystems. A correlation analysis was undertaken on phosphorus fractions, particle size fractions, soil pH and organic matter contents. Labile inorganic P (labile Pi) fractions correlated significantly with soil HCl-extractable Pi concentrations and soil pH. No significant correlations were found between labile phosphorus and any organic phosphorus pools or particle size fractions. Alfalfa ( Medicago sativa L.) was grown in small quantities of soil and then P fractionations were carried out on the alfalfa-depleted and original soils. Alfalfa consistently depleted labile inorganic phosphorus fractions in all soils, and in five of the nine soils, inorganic phosphorus associated with calcium phosphate minerals and/or Al or Fe hydrous oxides were significantly depleted under cultivation. The bicarbonate extracted organic phosphorus fraction was significantly depleted in one soil, but no other organic phosphorus fractions were significantly depleted by the alfalfa treatment. These results suggest that inorganic P fractions are critical sources of phosphorus in the traditional agroecosystems studied, and that soil calcium phosphate contents may in part determine where continually cultivated agriculture can be sustained without the use of synthetic fertilizers.

Nitrogen Loss from Coffee Agroecosystems in Costa Rica: Leaching and Denitrification in the Presence and Absence of Shade Trees

AbstractCoffee (Coffea arabica L.) management in Costa Rica is changing from traditional agroecosystems, where coffee is grown beneath a tree overstory, to management systems where shade trees are removed and N fertilizer is applied at high rates (ca. 300 kg N ha−1 yr−1). Although fertilization increases coffee bean production, it also increases the potential for substantial loss of N to groundwater and the atmosphere. We investigated NO−3 leaching and the factors controlling denitrification in shaded and unshaded coffee plantations in the Central Valley of Costa Rica; both plantation types were fertilized with 300 kg N ha−1 yr−1. Nitrate leaching was quantified using porous ceramic cup lysimeters placed 60 cm below the soil surface. Losses were estimated by multiplying the soil water NO−3 concentration by the monthly soil water excess, determined as the difference between precipitation and actual evapotranspiration. In addition, a laboratory experiment was conducted to investigate the influence of NO−3, C, and O2 availability on N2O production and total denitrification (N2O‐N + N2‐N). Annual leaching losses of NO−3 were almost three times greater in unshaded plantations (24 kg NO−3‐N ha−1 yr−1) than those in shaded plantations (9 kg ha−1 yr−1). In contrast, mean total denitrification rates in control soil samples from shaded plantations were 60% higher (732 µg N2O‐N kg−1 d−1) than in unshaded plantations (455 µg N2O‐N kg−1 d−1). Carbon additions elicited the largest increase in denitrification, generating nearly a threefold increase (+ C = 8396 µg N2O‐N kg−1 d−1; −C = 2985 µg N2O‐N kg−1 d−1) in both plantation types. Anaerobic conditions also significantly increased denitriflcation (+ O2 = 4331 µg N2O‐N kg−1 d−1; µO2 = 6656 µg N2O‐N kg−1 d−1). In both plantation types, the potential for N loss via NO−3 leaching was small compared with that for gaseous N loss.

Biodiversity and pest management in agroecosystems

* Preface to the Second Edition * Acknowledgments * Introduction * Chapter 1. The Ecological Role of Biodiversity in Agriculture * Traditional Agroecosystems As Models of Biodiverse Farms * The Ecological Role of Biodiversity * The Nature of Biodiversity in Agroecosystems * Chapter 2. Agroecology and Pest Management * The Nature of Agricultural Habitats and its Relation to Pest Buildup * Crop Diversification and Biological Control * Chapter 3. Plant Diversity and Insect Stability in Agroecosystems * Ecological Theory * Theory Dilemmas * Chapter 4. Insect Manipulation Through Weed Management * Weeds As Sources of Insect Pests in Agroecosystems * The Role of Weeds in the Ecology of Natural Enemies * Insect Dynamics in Weed-Diversified Crop Systems * Isolating the Ecological Effects of Weed Diversity * Crop-Weed Management Considerations * Chapter 5. Insect Management in Multiple-Cropping Systems * Patterns of Insect Abundance in Polycultures * Herbivore Trends in Polycultures * Case Study 1: Maize Intercrops and Pest Attack * Case Study 2: Cassava Intercrops and Pest Incidence * Case Study 3: Reducing Stemborers in Africa * Living Mulches: A Special Type of Intercrop * Methodologies to Study Insect Dynamics in Polycultures * Management Considerations * Chapter 6. Insect Ecology in Orchards Under Cover-Crop Management * Selecting and Managing Cover Crops in Orchards * Case Study 1: Apple Orchards in California * Case Study 2: Pecan Orchards in Georgia * Case Study 3: Summer Cover Crops in Vineyards * Chapter 7. The Influence of Adjacent Habitats on Insect Populations in Crop Fields * Crop Edges and Insect Pests * Field Boundaries and Natural Enemies * Designing and Managing Borders * Case Study 1: Exchange of Arthropods at the Interface of Apple Orchards and Adjacent Woodlands * Manipulating Crop-Field Border Vegetation * Case Study 2: Biological Corridors in Vineyards * Case Study 3: Strip Management to Augment Predators * Chapter 8. The Dynamics of Insect Pests in Agroforestry Systems * The Effects of Trees in Agroforestry on Insect Pests * Designing Natural Successional Analog Agroforestry Systems * The Need for Further Research * Chapter 9. Designing Pest-Stable Vegetationally Diverse Agroecosystems * Monocultures and the Failure of Conventional Pest-Control Approaches * Towards Sustainable Agriculture * Requirements of Sustainable Agroecosystems * Designing Healthy Agroecosystems * Healthy Soils--Healthy Plants * Restoring Diversity in Agricultural Systems * Enhancing Surrounding Biodiversity * Case Study 1: Diversification of an Onion Agroecosystem in Michigan * Case Study 2: A Diversified Small Farming System in Chile * Conclusion * References * Index

Future of forest gardens in the Uvan uplands of Sri Lanka

Forest gardens are traditional agroecosystems in the humid tropics that have evolved a forestlike structure and as such are commonly thought to be a good example of sustainable agriculture. While this may be true in the sense of soil protection and maintenance of biodiversity, they are not necessarily maintainable in the context of competing land use in the landscape. Such appears to be the case of forest gardens in the uplands of Uva Province of Sri Lanka. This paper reports an agroecological analysis of forest gardens and other forms of land use in Uva, and discusses how this understanding can be used to make use of the good properties of forest gardens. It shows that although they have very real environmental and social benefits, they are unable to satisfy the material needs of a rural population undergoing demographic and cultural changes. However, the alternative land-use systems, both private smallholder and state owned, have serious deficiencies with respect to long-term sustainability, and it is essential to develop appropriate alternatives. It should be possible to design a smallholder farming system that incorporates the high productivity of market gardens (i.e., the cultivation of seasonal crops such as vegetables) with, at least, the high stability and biophysical sustainability of the forest garden. Considerable work still needs to be done on the design of such a system as well as the agency for its development and promotion. The paper treats the forest gardens of Uva as a case study from which some general conclusions can be drawn with respect to the conscious development of forest garden systems elsewhere in the tropics.