Agroforestry and Biodiversity Conservation in Tropical Landscapes

Götz Schroth, Gustavo A. B. da Fonseca, Celia A. Harvey, Claude Gascon, Heraldo L. Vasconcelos, Anne-Marie N. Izac, Götz Schroth, Gustavo A. B. da Fonseca, Celia A. Harvey, Claude Gascon, Heraldo L. Vasconcelos, Anne-Marie N. Izac

• Publisher: Island Press
• Year: 2013
• Print ISBN: 9781559633574, 9781559633567
• eBook ISBN: 9781597267441
• Subtopic: Ecology

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.

PART I

Conservation Biology and Landscape Ecology in the Tropics: A Framework for Agroforestry Applications

This part of the book introduces some major concepts of conservation biology and landscape ecology for application in tropical landscapes. Its intention is to provide the necessary background knowledge in conservation science with a focus on landscape-scale issues so that nonspecialist readers can easily follow the discussions of the biodiversity effects of different types of agroforestry in later chapters. For readers who are familiar with the concepts, it provides an update of recent progress in these fields.

Chapter 1 outlines the current threats to biodiversity in the tropics, including habitat loss, fragmentation, overexploitation of ecosystems, and invasions by exotic plant and animal species. It discusses different conservation strategies and stresses the need for strategies comprising landscapes, regions, and larger scales. It points to the role in local, regional, and global conservation strategies that agroforestry can and cannot play: although protected areas and conservation set-asides are the irreplaceable backbone of any sensible conservation strategy, agroforestry can play an important supporting role by linking and buffering reserves and by maintaining or reintroducing a modest level of biodiversity in biologically degraded areas from which natural vegetation has been lost through human land use.

Chapters 2 and 3 focus on landscape processes that could be influenced by agroforestry practices. Chapter 2 discusses the demographic and genetic consequences of fragmentation of natural ecosystems through human land use for plant and animal populations and the key landscape features (area, edge, matrix, and distance effects) that affect fragmented populations. It also addresses the possibility of agroforestry land uses partially mitigating some of the negative effects of habitat fragmentation by reducing edge effects, increasing fragment connectivity, providing food or shelter for fragmented wildlife populations, and reducing the use of fire.

Chapter 3 discusses the potential role that agroforestry elements in the agricultural matrix could play in increasing landscape connectivity by serving as biological corridors for fauna and flora between remnant forest fragments. As experiences from corridors of natural vegetation show, the effectiveness of corridors for different plant and animal groups depends greatly on their size, structure, and floristic composition and on the biology of the target plant or animal species, and such background information must be taken into account in evaluating and designing agroforestry corridors.

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.

Figure 1.1. Distribution of world wide forest s by (a) genheral forest type and (b) tropial frest type (after FAO 001).Tropical 47%

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, ...

Table of contents

• About Island Press
• Title Page
• Copyright Page
• Table of Contents
• Preface
• Introduction: 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
• PART II - The Ecological Economics of Agroforestry: Environmental Benefits and Effects on Deforestation
• PART III - The Biodiversity of Agroforestry Systems: Habitat, Biological Corridor, and Buffer for Protected Areas
• PART IV - Biodiversity as Burden and Natural Capital: Interactions between Agroforestry Areas, Natural Ecosystems, and Rural Communities in Tropical Land Use Mosaics
• PART V - Matrix Management in Practice: Agroforestry Tools in Landscape Conservation
• Conclusion: Agroforestry and Biodiversity Conservation in Tropical Landscapes
• About the Contributors
• Index
• Island Press Board of Directors