Managing biological and genetic diversity in tropical agroforestry

Agroforestry Systems - The issues of biological and genetic diversity management in agroforestry are extremely complex. This paper focuses on genetic diversity management and its implications for...     

Bird communities in tropical agroforestry ecosystems: an underappreciated conservation resource

Tropical conservation and research focus primarily on protected areas and often ignore conservation values of surrounding agricultural lands. Understanding how species utilize agricultural land will maximize conservation efforts. We compared bird community composition in four habitats in northeastern Costa Rica: shade-grown cacao, live fences, riparian forest buffers, and preserved late-successional rainforest. Point counts over 2 months found 167 species from 36 families. Rainforest contained the most species unique to a habitat although richness per point was lower than in agricultural habitats. Half, 31, of the rainforest species did not occur in other habitats, while 106 species, mostly those preferring open areas, occurred in agroforest habitats but not rainforest. While agricultural habitats had fairly similar species composition to each other as determined by distance in an ordination, each also contained significant numbers, 9–30, of unique species. While intact rainforest remains central to conservation of tropical birds, agricultural lands with substantial trees, e.g., live fences, riparian buffers, and plantations with shade trees, can support a high richness of birds. These avian communities are not simply subsets of the rainforest species but include substantial numbers of unique species. Conservation contributions of these lands to species richness and complexity should be considered in conservation, and trees in these habitats preserved.     

Tree domestication in tropical agroforestry

Agroforestry Systems - We execute tree ‘domestication’ as a farmer-driven and market-led process, which matches the intraspecific diversity of locally important trees to the needs of...     

Biophysical interactions in tropical agroforestry systems

The rate and extent to which biophysical resources are captured and utilized by the components of an agroforestry system are determined by the nature and intensity of interactions between the components. The net effect of these interactions is often determined by the influence of the tree component on the other component(s) and/or on the overall system, and is expressed in terms of such quantifiable responses as soil fertility changes, microclimate modification, resource (water, nutrients, and light) availability and utilization, pest and disease incidence, and allelopathy. The paper reviews such manifestations of biophysical interactions in major simultaneous (e.g., hedgerow intercropping and trees on croplands) and sequential (e.g., planted tree fallows) agroforestry systems. In hedgerow intercropping (HI), the hedge/crop interactions are dominated by soil fertility improvement and competition for growth resources. Higher crop yields in HI than in sole cropping are noted mostly in inherently fertile soils in humid and subhumid tropics, and are caused by large fertility improvement relative to the effects of competition. But, yield increases are rare in semiarid tropics and infertile acid soils because fertility improvement does not offset the large competitive effect of hedgerows with crops for water and/or nutrients. Whereas improved soil fertility and microclimate positively influence crop yields underneath the canopies of scattered trees in semiarid climates, intense shading caused by large, evergreen trees negatively affects the yields. Trees in boundary plantings compete with crops for above- and belowground resources, with belowground competition of trees often extending beyond their crown areas. The major biophysical interactions in improved planted fallows are improvement of soil nitrogen status and reduction of weeds in the fallow phase, and increased crop yields in the subsequent cropping phase. In such systems, the negative effects of competition and micro-climate modification are avoided in the absence of direct tree–crop interactions. Future research on biophysical interactions should concentrate on (1) exploiting the diversity that exists within and between species of trees, (2) determining interactions between systems at different spatial (farm and landscape) and temporal scales, (3) improving understanding of belowground interactions, (4) assessing the environmental implications of agroforestry, particularly in the humid tropics, and (5) devising management schedules for agroforestry components in order to maximize benefits. This revised version was published online in June 2006 with corrections to the Cover Date.     

隆回县候鸟种类与迁徙路线调查报告

对湖南省隆回县候鸟种类及迁徙路线的调查结果表明,隆回县候鸟资源较为丰富,共记录鸟类26科95种,其中国家Ⅱ级保护鸟类18种。同时确定了该地区主要候鸟类迁徙停歇地及春秋两季迁徙路线,为该地区鸟类资源的有效保护和管理提供了科学依据。     

Managing native and non-native plants in agroforestry systems

Indigenous knowledge has influenced native species selection in agroforestry systems worldwide. However, scientific advancements in plant sciences, agroforestry technologies and trade have accelerated species movements and establishment beyond their native range. Managing native and non-native species is an important area of research in agroforestry and this thematic issue includes 13 papers that cover a range of topics from the role of non-native species in agroforestry to management interventions to improve yield. As evident from these papers, non-native plants are still an important component of agroforestry in many parts of the world. Whether native or non-native, management interventions can increase the economic, environmental and social values of these species and that of agroforestry. Collectively, these papers attest to the increasing body of foundational knowledge in agroforestry.     

Homegarden agroforestry systems: an intermediary for biodiversity conservation in Bangladesh

Biodiversity conservation is one of the important ecosystem services that has been negatively impacted by anthropogenic activities. Natural forests (NF) harbor some of the highest species diversity around the world. However, deforestation and degradation have resulted in reduced forest land cover and loss of diversity. Homegarden agroforestry (AF) systems have been proven to be an intermediary for biodiversity conservation. In this study, we evaluate the effectiveness of home garden AF practices to conserve tree species diversity in Bangladesh and compare them with tree species diversity in NF. A total of nine locations were selected for this synthesis from published literature which comprised of five AF sites and four NFs. Shannon?CWeiner Diversity Index (H) was similar for home-garden AF (3.50) and NF (2.99), with no statistical difference between them. Based on non-metric multi-dimensional scaling (NMDS) ordination analysis, the AF and NF plots showed distinct separation. However, Bray?CCurtis dissimilarity index ranged from 0.95 to 0.70 indicating nearly no overlap in species composition to significant overlap between AF and NF. Based on our results, we conclude that AF can serve as an important ecological tool in conserving tree species diversity, particularly on landscapes where NF fragments represent only a small fraction of the total land area. Creating and maintaining AF habitats in such human dominated landscapes should be part of the biodiversity conservation strategy.     

Evolution of agroforestry in the Xishuangbanna region of tropical China

A review of agroforestry practices in one lowland and one highland community of Xishuangbanna [Yunnan, P.R. China] has been carried out. Multilayer homegardens and taungya for fuelwood in the lowlands, tea shaded by natural forest and shellac production in a swidden farming system in the highlands are described. The extention of these agroforestry systems in Xishuangbanna is analyzed.Farming systems are facing problems related to shifting cultivation and to a rapid development of rubber which induce a negative evolution of these agroforestry systems.New agroforestry patterns based on Chinese research work, with rubber trees or with shade medicinal plants, are in extension in villages and in state farms.

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Résumé Un inventaire des systèmes agroforestiers du Xishuangbanna [Yunnan, R.P. Chine] a été réalisé: jardins à plusieurs étages et production de bois feu par système de taungya dans un village de plaine, thé à l'ombre de forêt naturelle et production de gomme-lacque dans un système d'agriculture sur brûlis dans un village de montagne.Les systèmes de production sont confrontés aux problèmes liés à l'agriculture sur brûlis, et au développement de l'hévéa. Il en résulte des évolutions négatives de ces practiques agroforestières.De nouveaux modèles agroforestiers, à base d'hévéa ou de plantes médicinales d'ombre, se développent dans les villages et dans les fermes d'état á la suite des travaux de la recherche chinoise.

     

Implications of Mayan agroforestry for biodiversity conservation in the Calakmul Biosphere Reserve,Mexico

Agroforestry for production and ecosystem health is a centuries-old form of ecosystem management used in many cultures indigenous to Mesoamerica, yet implications of such practices for biodiversity conservation are not well understood. Agroforestry systems were studied using interviews of farmers and field surveys of tree and bird diversity in three communities surrounding the Calakmul Biosphere Reserve in Campeche, Mexico to examine how differences in forest management practices affect forest biodiversity. Tree diversity and bird species richness were higher in areas surrounding communities that generated a greater variety of forest products and that cultivated “restoration trees,” species planted to aid in regeneration of mature forest. We conclude that traditional ecosystem management methods in areas surrounding natural reserves as practiced by inhabitants who depend on resources in the reserve for survival are compatible with maintaining and perhaps enhancing diversity of bird and tree communities at the site level.     

Insect pest problems in tropical agroforestry systems: Contributory factors and strategies for management

Agroforestry trees are attacked by a wide spectrum of insects at all stages of their growth just like other annual and perennial crops. Pest management in agroforestry has not received much attention so far, but recent emphasis on producing high value tree products in agroforestry and using improved germplasm in traditional systems, and emergence of serious pest problems in some promising agroforestry systems have increased awareness on risks posed by pests. Insects may attack one or more species within a system and across systems in the landscape, so pest management strategies should depend on the nature of the insect and magnitude of its damage. Although greater plant diversity in agroforestry is expected to increase beneficial arthropods, diversity by itself may not reduce pests. Introduction of tree germplasm from a narrow genetic base and intensive use of trees may lead to pest outbreaks. In simultaneous agroforestry systems, a number of factors governing tree—crop—environment interactions, such as diversity of plant species, host range of the pests, microclimate, spatial arrangement and tree management modify pest infestations by affecting populations of both herbivores and natural enemies. Trees also affect pest infestations by acting as barriers to movement of insects, masking the odours emitted by other components of the system and sheltering herbivores and natural enemies. In sequential agroforestry systems, it is mostly the soil-borne and diapausing insects that cause and perpetuate damage to the common hosts in tree—crop rotations over seasons or years. An integrated approach combining host-plant resistance to pests, exploiting alternative tree species, measures that prevent pest build up but favour natural enemies and biological control is suggested for managing pests in agroforestry. Species substitution to avoid pests is feasible only if trees are grown for ecological services such as soil conservation and low value products such as fuelwood, but not for trees yielding specific and high value products. For exploiting biological control as a potent, low cost and environmentally safe tool for pest management in agroforestry, research should focus on understanding the influence of ecological and management factors on the dynamics of insect pest-natural enemy populations. Scientists and policy makers in national and international institutions, and donors are urged to pay more attention to pest problems in agroforestry to harness the potential benefits of agroforestry.This revised version was published online in November 2005 with corrections to the Cover Date.     

Effect of perennial mulches on moisture conservation and soil-building properties through agroforestry

The effect of perennial mulches on moisture status, soil characteristics and on crop yields (maize-wheat rotation) was evaluated from 1986 through 1989 in a silty loam acidic soil (pH 5.6, PWP 11.4 & FC 25.6%) at the Research Farm of the Central Soil & Water Conservation Research & Training Institute, Dahra Dun. Mulch materials, comprised of leaves of Leucaena leucocephala, Eucalyptus hybrid, Shorea robusta, Broussonatia paprifera or Puerarua hirsuta (chopped) @ 4 t/ha were applied just after sowing of wheat and the residual effect of applied mulch was seen in kharif maize each year.The distribution of profile moisture revealed that at the time of sowing of wheat the soil water content did not differ with depth (0–90 cm). With the advancement of time, the magnitude of moisture distribution changed. At various crop growth stages the highest amount of water was found in the plots mulched with S. robusta followed by E. hybrid. All the mulch materials, except B. paprifera, lowered the soil pH, the maximum effect was noted with E. hybrid (pH reduced from 5.6 to 5.0). After three years, N and K content of soil were found to be greatest with the application of L. leucocephala whereas the highest P content was observed in B. paprifera mulched plots.The highest wheat grain yield (2.46 t/ha) was recorded with L. leucocephala and minimum under control (2.11 t/ha) which represents a gain of 11.7 per cent. Maximum maize grain yield (0.73 t/ha) was found in S. robusta mulched plots followed by L. leucocephala (0.63 t/ha) and the minimum in the control (0.51 t/ha).     

The impact of climate change on the growth of tropical agroforestry tree seedlings

Several studies have been conducted on the response of crops to greater concentrations of atmospheric CO₂ (CO₂ fertilization) as a result of climate change, but only few studies have evaluated this effect on multipurpose agroforestry tree species in tropical environments. The objectives of this study were to quantify differences in growth parameters and in leaf carbon (C) and nitrogen (N) concentrations of Cedrela odorata L. and Gliricidia sepium (Jacq.) Walp. seedlings under current ambient temperature (32°C daytime, 22°C night time) and CO₂ (360 ppm) (AMB); CO₂ fertilization (800 ppm, 32°C daytime, 22°C night time) (_fCO₂); elevated ambient temperature (360 ppm, 34°C daytime, 25°C night time) (TEMP); and a combination of elevated temperature (32°C daytime, 22°C night time) and CO₂ fertilization (800 ppm) (TEMPx_fCO₂). Results showed significant differences (P < 0.05) in seedling growth parameters (seedling height, number of stem leaves, leaf area ratio, shoot and root biomass, and shoot/root ratio) between treatments for both tree species. The greatest increases in growth parameters occurred in the TEMP and TEMPx_fCO₂ treatments compared to the AMB treatment for both tree species. However, growth parameters were significantly lower (P < 0.05) in the _fCO₂ treatment compared to that of the AMB treatment. Leaf N concentration was 1.1 to 2.1 times lower (P < 0.05) in all treatments when compared to current ambient conditions (AMB) in both tree species, but no significant changes in leaf C concentrations were observed. Results from our study suggested that _fCO₂ had the greatest negative impact on tree growth parameters, and leaf N concentrations were affected negatively in all treatments compared to current ambient conditions. It is expected that such changes in growth parameters and plant N content may impact the long-term cycling of nutrients in agroforestry systems.     

Directions in tropical agroforestry research: past, present, and future

Reflections on the past two decades of organized research in tropical agroforestry raise several issues. Research efforts started with an inductive and experiential approach but have subsequently followed a deductive and experimental approach that includes hypothesis testing and the development of predictive capability; agroforestry research is thus being transformed into a rigorous scientific activity. The research agenda, so far, has given high priority to soil fertility and other biophysical interactions, less priority to anthropological and sociological aspects, and little priority to evaluating costs and returns, pests and diseases, and the so-called non-timber forest (tree) products. Moreover, larger-spatial-scale issues, such as carbon sequestration, water quality, and biodiversity conservation, have been neglected because of the emphasis on field- and farm-scale studies. Overall, the high expectations that were raised about the role and potential of agroforestry as a development vehicle have not been fulfilled. In order to overcome this, it is imperative that research be focused on the generation of appropriate, science-based technologies of wide applicability, especially under resource-poor conditions and in smallholder farming systems. Future research agendas should entail a judicious blending of science and technology. Applied research should build upon the findings of basic research to generate technologies for application at the farm, regional and global levels. Such research should place increased focus on previously neglected subjects, for example, the exploitation of indigenous fruit-producing trees, the agronomic components of agroforestry systems, and the global issues mentioned above. Furthermore, an appropriate methodology that embodies economic, social, and environmental costs and benefits needs to be developed to realistically assess the impacts of agroforestry, and an enabling policy environment that will facilitate agroforestry adoption needs to be made available. Agroforestry research of the 21st century should strive to build bridges from the inductive phase of the past, through the deductive phase of the present, to the future phase of harnessing science and generating technologies for the benefit of the land and its present and future users. This revised version was published online in June 2006 with corrections to the Cover Date.     

Ecological interactions,management lessons and design tools in tropical agroforestry systems

During the 1980s, land- and labor-intensive simultaneous agroforestry systems (SAFS) were promoted in the tropics, based on the optimism on tree-crop niche differentiation and its potential for designing tree-crop mixtures using high tree-densities. In the 1990s it became clearer that although trees would yield crucial products and facilitate simultaneous growing of crops, they would also exert strong competitive effects on crops. In the meanwhile, a number of instruments for measuring the use of growth resources, exploratory and predictive models, and production assessment tools were developed to aid in understanding the opportunities and biophysical limits of SAFS. Following a review of the basic concepts of interspecific competition and facilitation between plants in general, this chapter synthesizes positive and negative effects of trees on crops, and discusses how these effects interact under different environmental resource conditions and how this imposes tradeoffs, biophysical limitations and management requirements in SAFS. The scope and limits of some of the research methods and tools, such as analytical and simulation models, that are available for assessing and predicting to a certain extent the productive outcome of SAFS are also discussed. The review brings out clearly the need for looking beyond yield performance in order to secure long-term management of farms and landscapes, by considering the environmental impacts and functions of SAFS.

     

Traditional agroforestry systems and biodiversity conservation in Benin (West Africa)

In the past, the conservation of biodiversity has been mostly understood in terms of the management of protected areas and natural forests, ignoring the possible role of farm areas and the ways through which rural communities have promoted biodiversity in their subsistence agricultural production systems. The present study focused on the floristic diversity within traditional agroforestry parkland systems around the Pendjari Biosphere Reserve in Benin and showed the diversity of tree species in the area as well as socio-economic factors which affect the practice of this farming system. We used questionnaires and interviewed a total of 118 households to collect data. Respondents were interviewed on their farms and during the interview; we inventoried the number of tree on the farm and determined the farm size. Twenty-one tree species belonging to 14 botanical families were recorded during the surveys and the average stand density of the woody component of farmlands was 7.97 ± 5.43 stems/ha. A number of both native and exotic tree species occurred in the parkland agroforestry systems with dominance of indigenous tree species. Species richness varied with the size of household where households with small land holding conserve more tree species in their field than households with large land holdings. 64% of households surveyed were making deliberate efforts to plant tree species on their farmlands. The most important reasons which determined household ambitions to conserve woody species on farmland were tree products contribution to food and medicine. Results also showed that respondents who noticed that trees were decreasing in the wild conserve more tree species on their farmlands. This research highlights the role of traditional agroforestry practices to support tree species richness and provides evidence of the farms’ role as biodiversity reservoirs.     

Carbon dynamics in small tropical catchments under preserved forest and cacao agroforestry systems

Agroforestry Systems - Inland waters such as streams that receive carbon from terrestrial landscapes usually have a net heterotrophic metabolism and emit significant amounts of CO2 to the...     

Planning methods for agroforestry

One of the major issues facing the world is the interrelated problem of deforestation and concurrent degradation of agricultural lands in tropical and subtropical nations. Agroforestry is one technique to help alleviate this problem. Implementation of newly developed agroforestry techniques in various places all over the world, has made it clear that:

Problem solving cannot be limited to the individual farmstead or plot level from a social and ecological point of view.

Existing landscapes present both constraints and opportunities for further land development.

More appropriate agroforestry techniques can be applied by classifying landscape units and existing land-use systems.

Planning is necessary because agroforestry requires a holistic perspective to be sustained during the long time necessary for implementation.

For these reasons, a review of planning methods used in agroforestry and suggestions for their improvement seems timely. Selected existing methods, with an emphasis on those being used in Kenya, are analyzed in terms of goals, community needs, site assesment, options for action, implementation, management, and evaluation. Our review was conducted through literature survey and interviews with key informants in Nairobi, Kenya; Wageningen, the Netherlands; and Washington, D.C., U.S.A. Landscape planning might be an approach that can be used with agroforestry to provide a more comprehensive perspective. The role of landscape planning in agroforestry projects is discussed in detail, using a study from Kenya for illustration.     

Why tree-crop interactions in agroforestry appear at odds with tree-grass interactions in tropical savannahs

This paper describes recent research findings on resource sharing between trees and crops in the semiarid tropics and attempts to reconcile this information with current knowledge of the interactions between savannah trees and understorey vegetation by examining agroforestry systems from the perspective of succession. In general, productivity of natural vegetation under savannah trees increases as rainfall decreases, while the opposite occurs in agroforestry. One explanation is that in the savannah, the beneficial effects of microclimatic improvements (e.g. lower temperatures and evaporation losses) are greater in more xeric environments. Mature savannah trees have a high proportion of woody above-ground structure compared to foliage, so that the amount of water 'saved' (largely by reduction in soil evaporation) is greater than water 'lost' through transpiration by trees. By contrast, in agroforestry practices such as alley cropping where tree density is high, any beneficial effects of the trees on microclimate are negated by reductions in soil moisture due to increasing interception losses and tree transpiration. While investment in woody structure can improve the water economy beneath agroforestry trees, it inevitably reduces the growth rate of the trees and thus increases the time required for improved understorey productivity. Therefore, agroforesters prefer trees with more direct and immediate benefits to farmers. The greatest opportunity for simultaneous agroforestry practices is therefore to fill niches within the landscape where resources are currently under-utilised by crops. In this way, agroforestry can mimic the large scale patch dynamics and successional progression of a natural ecosystem. This revised version was published online in June 2006 with corrections to the Cover Date.