Agroforestry -- the practice of integrating trees and other large woody perennials on farms and throughout the agricultural landscape -- is increasingly recognized as a useful and promising strategy that diversifies production for greater social, economic, and environmental benefits. Agroforestry and BiodiversityConservation in Tropical Landscapes brings together 46 scientists and practitioners from 13 countries with decades of field experience in tropical regions to explore how agroforestry practices can help promote biodiversity conservation in human-dominated landscapes, to synthesize the current state of knowledge in the field, and to identify areas where further research is needed.
Agroforestry and Biodiversity Conservation in Tropical Landscapes is the first comprehensive synthesis of the role of agroforestry systems in conserving biodiversity in tropical landscapes, and contains in-depth review chapters of most agroforestry systems, with examples from many different countries. It is a valuable source of information for scientists, researchers, professors, and students in the fields of conservation biology, resource management, tropical ecology, rural development, agroforestry, and agroecology.
Agroforestry -- the practice of integrating trees and other large woody perennials on farms and throughout the agricultural landscape -- is increasingly recognized as a useful and promising strategy that diversifies production for greater social, economic, and environmental benefits. Agroforestry and BiodiversityConservation in Tropical Landscapes brings together 46 scientists and practitioners from 13 countries with decades of field experience in tropical regions to explore how agroforestry practices can help promote biodiversity conservation in human-dominated landscapes, to synthesize the current state of knowledge in the field, and to identify areas where further research is needed.
Agroforestry and Biodiversity Conservation in Tropical Landscapes is the first comprehensive synthesis of the role of agroforestry systems in conserving biodiversity in tropical landscapes, and contains in-depth review chapters of most agroforestry systems, with examples from many different countries. It is a valuable source of information for scientists, researchers, professors, and students in the fields of conservation biology, resource management, tropical ecology, rural development, agroforestry, and agroecology.
Agroforestry and Biodiversity Conservation in Tropical Landscapes
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Overview
Agroforestry -- the practice of integrating trees and other large woody perennials on farms and throughout the agricultural landscape -- is increasingly recognized as a useful and promising strategy that diversifies production for greater social, economic, and environmental benefits. Agroforestry and BiodiversityConservation in Tropical Landscapes brings together 46 scientists and practitioners from 13 countries with decades of field experience in tropical regions to explore how agroforestry practices can help promote biodiversity conservation in human-dominated landscapes, to synthesize the current state of knowledge in the field, and to identify areas where further research is needed.
Agroforestry and Biodiversity Conservation in Tropical Landscapes is the first comprehensive synthesis of the role of agroforestry systems in conserving biodiversity in tropical landscapes, and contains in-depth review chapters of most agroforestry systems, with examples from many different countries. It is a valuable source of information for scientists, researchers, professors, and students in the fields of conservation biology, resource management, tropical ecology, rural development, agroforestry, and agroecology.
Product Details
| ISBN-13: | 9781597267441 |
|---|---|
| Publisher: | Island Press |
| Publication date: | 03/22/2013 |
| Sold by: | Barnes & Noble |
| Format: | eBook |
| Pages: | 575 |
| File size: | 20 MB |
| Note: | This product may take a few minutes to download. |
About the Author
Götz Schroth is with the Center for International Forestry Research in Brazil.
Gustavo A.B. Da Fonseca is with Conservation International, USA.
Celia Harvey is professor at the Centro Agronomico de Investigacion y Ensenanza in Costa Rica.
Claude Gascon is with Conservation International, USA.
Heraldo L. Vasconcelos is professor at the Federal University of Uberlândia in Manaus, Brazil.
Anne-Marie N. Izac is at the Centre de Coopération Internationale en Recherche Agronomique pour le Développement (CIRAD) in France.
Read an Excerpt
Agroforestry and Biodiversity Conservation in Tropical Landscapes
By Schroth Götz, Gustavo A. B. da Fonseca, Celia A. Harvey
ISLAND PRESS
Copyright © 2004 Island PressAll rights reserved.
ISBN: 978-1-59726-744-1
CHAPTER 1
Biodiversity Conservation in Deforested and Fragmented Tropical Landscapes: An Overview
Claude Gascon, Gustavo A. B. da Fonseca, Wes Sechrest, Kaycie A. Billmark, and James Sanderson
Our planet is in the midst of a sixth mass extinction. The earth is losing its biological resources at an ever-increasing rate, a trend that began with the emergence of humans. The majority of the earth's land surface has been colonized over the last few tens of thousands of years and was increasingly affected by the agricultural revolution around 10,000 years BP and the industrial revolution in more recent times. If this trajectory is maintained, many of the planet's biological resources will disappear. There is a need for a more thorough scientific understanding of natural systems and their functioning as a base for crucial global, regional, and local conservation decisions. The earth's tropical regions, in particular, are highly vulnerable to human impact. The wealth and distinctiveness of their biodiversity, combined with the multifaceted threats that they face make these regions an urgent priority for biodiversity conservation. Current scientific research efforts in tropical areas have yielded insight into many important biological questions. Conservation actions, including the implementation of protected areas and corridors, and attention to the surrounding matrix of agricultural and degraded land must be integrated into cohesive regional plans. The application of more conservation-friendly land uses, such as agroforestry, for improving biodiversity conservation in tropical landscapes can contribute to such landscape-scale conservation strategies. The implementation of these efforts is an important step in translating science into effective conservation action.
The goal of this chapter is to provide an overview of important global biodiversity conservation issues, with special attention to terrestrial tropical ecosystems. Additionally, this chapter provides a framework for the discussions in later chapters with regard to biodiversity threats and conservation strategies and applications, including agroforestry.
Tropical Ecosystems
Tropical ecosystems cover a large part of the earth's surface and contain more than half of all terrestrial species (Myers and Myers 1992). These ecosystems have played a unique role in the evolution of the planet's biodiversity. Tropical environments, especially humid forests, were once much more widespread than at present. Today, approximately half of all tropical regions are forests, with the remainder savannas and deserts. Worldwide, there are about 3.87 billion ha of forest, 5 percent of which are forest plantations (FAO 2001). World forests may be categorized as tropical, subtropical, temperate, or boreal (Figure 1.1a). Tropical forests consist of tropical rain, tropical moist deciduous, tropical dry, and tropical mountain forests (Figure 1.1b).
All forests are affected on some level by direct and indirect human activity, although there are no accurate global assessments of forest conditions. Between 1990 and 2000, 14.2 million ha per year of tropical forest were deforested, with an additional 1 million ha per year converted to forest plantations. Natural forest expansion over this time was 1 million ha per year, with an additional 0.9 million ha per year afforested by humans as forest plantations. This deforestation occurred differently on regional and local scales. For instance, during this 10-year time period, the country of Burundi in Central Africa lost 9 percent of its remaining forest per year. This significant percentage loss is of great importance to national policymakers in Burundi, but actual deforestation rates of 15,000 ha per year were much lower than in other parts of the world and therefore are less important from a global perspective. The largest actual loss in Africa occurred in the Sudan, with 959,000 ha deforested each year. Indonesia deforested a staggering 1,312,000 ha per year over this time period (FAO 2001). If left unchecked, the clearing, burning, logging, and fragmentation of forest will destroy most of the world's tropical forests in our lifetime. The planet's forested areas have already decreased by almost 2 billion ha since the beginning of the agricultural revolution (Noble and Dirzo 1997). The impacts of this destruction on any geographic scale are not yet fully understood. In addition to the release of CO2 via biomass combustion and microbial activity, soil erosion, and hydrological cycle disturbance, this destruction also results in the extinction of numerous known populations and species and the loss of undiscovered species, each with a unique history and habits never to be known.
One important tool for mitigating tropical deforestation is the establishment of tropical agroforested areas or protected parks. Parks are effective in preventing deforestation and thereby protect biodiversity despite the fact that many are underfunded and experience substantial land use pressure (Bruner et al. 2001). Within the matrix surrounding tropical parks, other methods, such as agroforestry, can be used to protect biodiversity and help alleviate the negative effects of deforestation and associated edge effects. By simulating to some extent natural forest cover through the cultivation of tree species with agricultural crops, agroforestry areas may serve as biodiversity corridors between protected areas and nonprotected remnants of natural vegetation while providing sustainable crop and wood harvests.
The Tropical Biodiversity Crisis
Biodiversity is not simply a measure of the world's species; rather, it also encompasses genetic variability within and between populations, species' evolutionary histories, and other measures of the diversity of life. Biodiversity patterns vary between regions. This variability results both from the present ecology and past evolutionary history of species and from habitat type, habitat availability, and physical qualities such as climatic conditions and geological and hydrological patterns, all varying over space and time. The future preservation of biodiversity requires intricate knowledge of the patterns and processes that affect ecosystem function. The tropics, particularly tropical forests, are expansive biodiversity reservoirs (Stevens 1989). Many species in the tropics are limited in distribution, and the spatial turnover of species is high among many taxonomic groups (Condit et al. 2002). Species distribution patterns are not uniform across the globe; most groups of organisms show a strong increase in species richness, or number of species per unit area, nearer to the equator. Additionally, the number of species in most terrestrial and freshwater groups is greater at lower than at higher elevations and greater in forests than in deserts (Gaston 2000). These general patterns suggest that tropical environments are favorable to the evolution of new species and the persistence of existing species. High diversity in the tropics is generally attributed to high productivity, low environmental variance (e.g., seasonality), persistent predation and competition, lower historical climatic change impacts, and differential speciation and extinction rates. Recognizing that these attributes tend to support high diversity in the tropics, it is important to note that there are significant intratropical diversity patterns and that lower-diversity regions can also be found in the tropics.
Conservation efforts have focused much attention on tropical forests because they are the richest strongholds of terrestrial biodiversity. Therefore, exploitation of natural resources in the tropics results in the destruction of large genetic reservoirs. Incalculable benefits are gained from maintaining species numbers and the current diversity of organisms. Much of the research on ecological and evolutionary benefits is new, and more research must be conducted to determine broad patterns and processes. Research has shown that on local scales, the lower the species diversity within a system, the more vulnerable it is to species and population extinctions as a result of nonnative species invasions (Levine 2000). One can conclude that the maintenance of high diversity could reduce the number of invading species, thereby greatly reducing the negative impacts of these species (Kennedy et al. 2002). Other biodiversity effects on ecosystem processes have also been demonstrated (Cardinale et al. 2002). For example, plant diversity of European grasslands positively influences plant primary production (Loreau and Hector 2001). Additionally, diverse areas tend not only to have more functional components (more species with diverse ecologies) but also to maintain more predictable ecological processes (McGrady-Steed et al. 1997).
Unfortunately, short-term economic gains driven by increasing human populations usually influence the decision-making process that leads to resource overuse. High population growth rates in tropical countries create socioeconomic difficulties. Environmental constraints, such as climate, often compound prevalent problems such as malnutrition and famine. This situation, combined with the need of tropical countries to rely on more advanced countries for technical assistance and for the development of their own resources, often leads to exploitive rather than sustainable use. Poverty, war, and social inequality generate environmental degradation, which further drives socioeconomic crises in a continuous feedback loop. These underlying drivers of environmental degradation and biodiversity loss must be addressed for successful conservation of tropical ecosystems.
Threats to Tropical Forest Ecosystems
Environmental degradation is driven by several major threats, including habitat loss and fragmentation, exploitation, pollution, introductions of nonnative species, and human-induced global change. For tropical ecosystems, land use is ranked as the major driver affecting these regions for the next 100 years (Sala et al. 2000). In this section we briefly review these threats and point to the potential role of agroforestry that will be discussed in more detail in subsequent chapters.
Habitat Fragmentation
Although human presence affects landscape biodiversity in many ways, one of the most visible and widespread effects is habitat fragmentation (Gascon et al. 2003). Because of the dynamic nature of landscapes, fragmentation alters the behavior of natural interactions within the landscape and the functioning of the entire landscape. For example, the species composition and diversity of a tropical landscape differ near a treefall as compared with a dense canopy. However, the temporal recovery of treefalls over an entire tropical landscape results in areas at all stages of natural forest growth. These areas provide a varying but consistent species composition and diversity for the entire landscape. Conversely, in fragmented landscapes, the number of areas at different stages of forest growth is lower, and the average functioning of the landscape becomes less predictable. If a substantial portion of a tropical landscape undergoes deforestation, the ecological function of the fragmented landscape can be permanently altered from its natural state. These changes in the biodiversity and integrity of fragmented landscapes argue in favor of the construction of conservation corridors, where biodiversity-friendly land uses such as agroforestry can be integrated with fragments of natural habitat in interconnected networks that help restore functional aspects of the landscape.
Fragmentation alters not only the functioning of the landscape but also the behavior and dynamics of populations in the fragmented system (Bierregaard et al. 2001; Chapter 2, this volume). The response of populations to landscape changes often is very negative. If no patches exist that are habitable for a particular population, then that population is likely to be lost. Forest fragmentation can result in species population survival or extinction, depending on many factors such as how easily the species can disperse between forest patches and whether the species can use the modified landscape and find resources. For instance, nocturnal species may be better able to survive fragmentation than their diurnal counterparts because of the greater similarity of ambient conditions between forest fragments and the surrounding matrix at night (Daily and Ehrlich 1996). Fragmentation has also been shown to decrease aboveground biomass, especially on the fragment edges (Laurance et al. 1997). A study in Brazil showed that large canopy trees in tropical rainforests experience a higher mortality rate when they are in a heavily fragmented system (Laurance et al. 2000). Fragmentation also affects the reproduction of species that remain in the forest patches. For example, species of dipterocarp trees that inhabit lowland forests of Borneo exhibit seed dispersal events that coincide with El Niño–Southern Oscillation events. Because these dipterocarp species are dominant canopy species, their dispersal and reproduction are strongly affected by local and regional logging, which can disrupt their timed reproduction (Curran et al. 1999).
Finally, tropical forest fragmentation can differentially affect species dispersal mechanisms on a landscape scale (Aldrich and Hamrick 1999; see also Chapter 3, this volume). Metapopulation dynamics between habitat patches result in local population extinctions, causing diversity losses in patches that are often unrecoverable in large expanses of degraded areas. Genetic isolation between widely isolated or dispersal- limited populations leads to loss of overall genetic diversity between populations and increasing vulnerability to deleterious genetic effects, such as susceptibility to pathogens. Landscape-scale strategies must use research on a broad base of ecosystems, species, and populations. For example, Madagascar, which holds a high amount of unique biodiversity, has lost more than 90 percent of its primary forest. Threats on the island have not abated, and forest losses continue in the few remaining fragments. The medium-term existence of many tropical forest species is threatened by widespread forest loss and fragmentation.
Introduced Species
A biodiversity concern related to fragmentation is that of introduced species. Tropical regions have a large number of endemic species that are unique to a particular area or region, usually because of genetic isolation created by physical barriers (e.g., water in the case of island species). Often in the case of disturbed areas, such as in fragmented systems, local endemic species are replaced by wide-ranging species, including those tolerant of disturbed habitats (Tocher et al. 2001). Successful nonnative species often are ones that range over wide areas and tolerate disturbance well. Globally, almost all areas are affected by these introduced species, with island biota being especially vulnerable. Changes in complex ecological systems, such as introduction of prey species, can have cascading effects on fauna (Roemer et al. 2002). Invasive species are homogenizing the global flora and fauna, which has led to extinctions and population reductions of native species (Lovel 1997).
This negative impact on native species is sometimes masked by an increase in species richness. With the influx of competing species, species numbers in a fragmented system can increase, which creates a situation in which further biodiversity degradation can occur through species displacements and more local extinctions. To mitigate these problems, direct preventive measures are needed in addition to increases in connectivity, area-to-perimeter ratios, buffer zones, and improvements to the matrix around existing reserves (Gascon et al. 2000). The use of agroforestry outside protected areas may play a role in such strategies by increasing connectivity and serving as buffers but may also pose additional threats if invasive alien tree species are used (see Chapter 15, this volume).
(Continues...)
Excerpted from Agroforestry and Biodiversity Conservation in Tropical Landscapes by Schroth Götz, Gustavo A. B. da Fonseca, Celia A. Harvey. Copyright © 2004 Island Press. Excerpted by permission of ISLAND PRESS.
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Table of Contents
PrefaceIntroduction: The Role of Agroforestry in Biodiversity Conservation in Tropical Landscapes
PART I. Conservation Biology and Landscape Ecology in the Tropics: A Framework for Agroforestry Applications
Chapter 1. Biodiversity Conservation in Deforested and Fragmented Tropical Landscapes: An Overview
Chapter 2. Ecological Effects of Habitat Fragmentation in the Tropics
Chapter 3. Landscape Connectivity and Biological Corridors
PART II. The Ecological Economics of Agroforestry: Environmental Benefits and Effects on Deforestation
Chapter 4. The Economic Valuation of Agroforestry's Environmental Services
Chapter 5. Is Agroforestry Likely to Reduce Deforestation?
Chapter 6. Chocolate Forests and Monocultures: A Historical Review of Cocoa Growing and Its Conflicting Role in Tropical Deforestation and Forest Conservation
Chapter 7. Achieving Biodiversity Conservation Using Conservation Concessions to Complement Agroforestry
PART III. The Biodiversity of Agroforestry Systems: Habitat, Biological Corridor, and Buffer for Protected Areas
Chapter 8. The Biodiversity and Conservation Potential of Shifting Cultivation Landscapes
Chapter 9. Biodiversity Conservation in Neotropical Coffee (Coffea arabica) Plantations
Chapter 10. Complex Agroforests: Their Structure, Diversity, and Potential Role in Landscape Conservation
Chapter 11. Live Fences, Isolated Trees, and Windbreaks: Tools for Conserving Biodiversity in Fragmented Tropical Landscapes
Chapter 12. Agroforestry Systems: Important Components in Conserving the Genetic Viability of Native Tropical Tree Species?
PART IV. Biodiversity as Burden and Natural Capital: Interactions between Agroforestry Areas, Natural Ecosystems, and Rural Communities in Tropical Land Use Mosaics
Chapter 13. Wildlife Conservation in Agroforestry Buffer Zones: Opportunities and Conflict
Chapter 14. Hunting in Agroforestry Systems and Landscapes: Conservation Implications in West-Central Africa and Southeast Asia
Chapter 15. Invasive Agroforestry Trees: Problems and Solutions
Chaper 16. Diseases in Tropical Agroforestry Landscapes: The Role of Biodiversity
PART V. Matrix Manangement in Practice: Agroforestry Tools in Landscape Conservation
Chapter 17. Agroforestry Buffer Zones and Stepping Stones: Tools for the Conservation of Fragmented Landscapes in the Brazilian Atlantic Forest
Chapter 18. Agroforestry and Biodiversity: Improving Conservation Outcomes in Tropical Northeastern Australia
Chapter 19. Silvopastoral Systems: Ecological and Socioeconomic Benefits and Migratory Bird Conservation
Chapter 20. Agroforestry and Climate Change–Integrated Conservation Strategies
Conclusion: Agroforestry and Biodiversity Conservation in Tropical Landscapes
About the Contributors
Index