Habitat Fragmentation and Landscape Change

An Ecological and Conservation Synthesis

David B. Lindenmayer, Joern Fischer, David B. Lindenmayer

• Publisher: Island Press
• Year: 2013
• Print ISBN:
  9781597260213
  9781597260206
• eBook ISBN:
  9781597266062
• Topic: Biological Sciences
• Subtopic: Ecology
• Index: Biological Sciences

Habitat loss and degradation that comes as a result of human activity is the single biggest threat to biodiversity in the world today. Habitat Fragmentation and Landscape Change is a groundbreaking work that brings together a wealth of information from a wide range of sources to define the ecological problems caused by landscape change and to highlight the relationships among landscape change, habitat fragmentation, and biodiversity conservation. The book:

• synthesizes a large body of information from the scientific literature
• considers key theoretical principles for examining and predicting effects
• examines the range of effects that can arise
• explores ways of mitigating impacts
• reviews approaches to studying the problem
• discusses knowledge gaps and future areas for research and management

Habitat Fragmentation and Landscape Change offers a unique mix of theoretical and practical information, outlining general principles and approaches and illustrating those principles with case studies from around the world. It represents a definitive overview and synthesis on the full range of topics that fall under the widely used but often vaguely defined term "habitat fragmentation."

CHAPTER 1

Introduction

Why This Book Was Written

This book was written for two main reasons. First, themes associated with landscape change have become a major focus of conservation biology and landscape ecology (McGarigal and Cushman 2002; Fahrig 2003; Hobbs and Yates 2003). A review of all papers published in 2001 in the journals Conservation Biology, Biological Conservation, and Biodiversity and Conservation found that landscape change and habitat fragmentation were the two most frequently studied processes threatening species persistence (Fazey et al. 2005a). Similarly, a database search of journal articles prior to writing this book produced over 2000 published papers where the abstract or keywords contained the words “habitat loss” or “habitat fragmentation.” Because the literature on landscape change and habitat fragmentation is so large and complex (and becoming increasingly so), we believe there is an important role for a book that provides an overview of the varied and interrelated topics encompassed by it.

The second reason we wrote this book was because the term “habitat fragmentation” has become vague and ambiguous due to its imprecise use, thereby limiting its practical value for conservation managers (Haila 2002; Regan et al. 2002). The term is losing its meaning because it is frequently used as an umbrella term for a wide range of interacting processes, including habitat loss, the subdivision of remaining habitat, an increase in edge effects, and altered species interactions or ecological processes. In essence, there are multiple processes grouped under the term “fragmentation,” and there are multiple consequences of those processes; thus it is difficult to determine which consequences relate to which process. As a result, the “blizzard of ecological details” characteristic of the fragmentation literature, coupled with the way the term “habitat fragmentation” often means “all things to all people,” has made the study of fragmentation a “panchreston” (Bunnell 1999a; see discussion in the next section). Given this, it is perhaps not surprising that even some major reviews of fragmentation (e.g., McGarigal and Cushman 2002) have failed to identify “clear insights into system dynamics” (Bissonette and Storch 2002). The “panchreston problem” is clearly hampering progress in the study of landscape change and ways to mitigate its negative impacts on species and ecosystems.

A possible way to gain a better understanding of the field is to disentangle the subcomponent parts and themes that have been collected under the umbrella of “fragmentation” research. We have tried to do this in our book by summarizing and identifying links between what we believe are key topics associated with landscape change, habitat loss, and habitat fragmentation. We emphasize the word “summarizing” here because we have attempted to provide a brief overview and synthesis of key topics, rather than an exhaustive review of each and every topic related to fragmentation.

“Disentangling” Habitat Fragmentation

Bunnell (1999a) argued that the generic term “habitat fragmentation” is often used loosely to encompass a myriad of processes and changes that accompany landscape alteration—making it a panchreston; which he defined as a proposed explanation intended to address a complex problem by trying to account for all possible contingencies but typically proving to be too broadly conceived and therefore oversimplified to be of any practical use.

The Random House Dictionary of the English Language [undated] cited in Bunnell (1999a).

Bunnell (1999a) argued that a solution to the problems created by the fragmentation panchreston was to acknowledge that multiple processes take place and to work in ways to separate them so that consequences can be better assigned to particular processes (see also Figure 1.1). Unfortunately, the fragmentation literature rarely does this. Instead, typically what occurs is that one pattern (the spatial distribution of a species or suite of species) is correlated with another pattern (the spatial distribution of patches of native vegetation), with little emphasis on the ecological processes that link the two. In this book, we argue that tackling the panchreston will help: (1) key questions to be better defined—a major issue because problem-definition is something that ecologists often do poorly (Peters 1991); (2) ensure better and more focused studies that contribute an improved understanding of the effects of landscape change on biota; and (3) more rapidly evolve improved conservation and resource management strategies (Box 1.1). For example, although habitat loss and habitat subdivision often go together (see Chapter 4), the distinction between them is important. This is because dealing with habitat loss will require formulating quite different kinds of hypotheses, quite different types of studies, and, ultimately, different kinds of mitigation strategies than if the focus is on habitat subdivision.

Figure 1.1. A conceptual model of landscape change effects on plants (redrawn from Hobbs and Yates 2003: reproduced with permission from the Australian Journal of Botany, 51, 471–488 [Hobbs, R.J. & Yates, C.J.]. Copyright CSIRO 2003. Published by CSIRO PUBLISHING, Melbourne VIC, Australia [ http://www.publish.csiro.au/journals/ajb ]).

While we argue that an important way forward is to focus on particular subcomponents of landscape modification, we also acknowledge the importance of recognizing the complexity that is typically associated with multiple biotic responses to multiple interacting processes of landscape change (Crome 1994). This is why we dedicate an entire section of this book (Part V) to approaches and general principles for mitigating the multiple threatening processes and negative effects on species and assemblages that often accompany landscape change.

The Scope of This Book: Definitions and Key Themes

Our overarching goal is to tackle the habitat fragmentation panchreston. To achieve this goal, we provide a conceptual framework for the study and management of modified landscapes. We also provide many empirical examples from around the world to give tangible support to this conceptual framework. An important part of tackling the fragmentation panchreston is to carefully define appropriate terms such as “habitat” and “fragmentation.” This is because the imprecise use of terminology can lead to the inappropriate use of concepts and theories in management (Murphy 1989) or inappropriate testing of theory (Fazey 2005). Given this, we have attempted to be as precise as possible in our use of terms throughout this book—although errors have undoubtedly crept in.

Definitions

Key terms that we use frequently throughout the text and that have a specific meaning in this book (sometimes different from standard usage in the literature) are outlined in Table 1.1. From an ecological perspective, what constitutes a landscape will usually be a function of the scales over which a given species moves and how it perceives its surrounds (Wiens 1997; Manning et al. 2004a). However, for the practical purposes of this book, we define the term “landscape” from a human perspective and consider it as an area that covers hundreds to thousands of hectares. When landscapes are changed by vegetation clearing or other kinds of anthropogenic modification, we use the interchangeable terms “landscape change,” “landscape alteration,” or “landscape modification.” We use the term “habitat” to mean the environments suitable for a particular species. Following this definition, habitat therefore is a species-specific entity (see Table 1.1). “Habitat loss” refers to the loss of suitable habitat for a given species such that the particular species no longer occurs in that area. We do not consider the term “habitat loss” to be synonymous with the loss of native vegetation. This is because a landscape extensively altered by humans where vegetation loss has been substantial may effectively experience no loss of suitable habitat for some species. Conversely, a landscape supporting a complete cover of native vegetation may contain no suitable habitat for some species (e.g., because of a lack of naturally suitable environmental conditions) (Table 1.2). Given this, much of this book labors the point about the importance of understanding what constitutes suitable habitat as a prelude to mitigating habitat loss. Habitat subdivision is the process of subdividing a single large area of habitat into several smaller areas, a practice that is also referred to as habitat fragmentation. We follow the logic of Fahrig (2003) in recognizing that the spatial process of habitat subdivision (habitat fragmentation) is distinctly different from the process of habitat loss. Moreover, we rarely use the term “habitat fragmentation” in the remainder of this book because of the confusion that its loose application can create.

Box 1.1. Why Disentangling Threatening Processes Is Important for Conservation: The Case of the Brown Treecreeper

Identifying which of the processes associated with landscape change are most threatening to a given species of conservation concern is critical for the development of efficient and effective conservation strategies. This is illustrated by the case of the southern subspecies of the brown treecreeper (Climacteris picumnus picumnus), a declining bird species in many woodland areas in southeastern Australia (Cooper and Walters 2002). The species is absent from, or has declined severely, in many remnants of apparently suitable woodland. For example, in Mulligan’s Flat Nature Reserve near Canberra, a previously stable population has declined over the last decade to a single individual in mid-2006 (J. Bounds, pers. comm.). Developing strategies to conserve the brown treecreeper depends on identifying the underlying reasons for its decline and low levels of patch occupancy.

Work on the brown treecreeper indicates that a lack of habitat connectivity and hence disrupted dispersal is the most likely reason for the decline of the species in landscapes subject to major human modification (Walters et al. 1999). Where woodland patches are isolated and the landscape between them is devoid of suitable habitat, brown treecreepers are often absent—even though some woodland patches are large and contain all the essential habitat components needed by the species (e.g., fallen logs and tree hollows; Cooper et al. 2002). Therefore, if a small population in a patch is lost, sources of dispersing animals may be too remote to reverse the local extinction. Conservation of the species will depend on ways to promote habitat connectivity. These may include revegetation programs to link remnants and promote natural dispersal, or “artificial dispersal” through translocation programs of birds to empty patches or patches with only a few remaining birds.

Table 1.1. The definition of key terms used widely throughout this book

Term	Definition	Chapter where discussed in detail
Species perspective of a modified landscape	The perception of a landscape as it is assumed to be experienced by a given (nonhuman) species; important features are assumed to include sources of food and shelter, sufficient space, and appropriate climatic conditions	Chapter 3
Human perspective of a modified landscape	The perception of a landscape as experienced by humans; features typically noted include patches of different types of land cover and their spatial arrangement (including native vegetation)	Chapter 3
Habitat	The environments suitable for a particular species—a species-specific entity	Chapter 4
Habitat loss	Loss of suitable habitat for a given species, making the area unsuitable for that species to occur there	Chapter 4
Habitat degradation	The reduction in quality of an area of habitat for a given species. The species may still occur in the area but, for example, may not be able to successfully breed there	Chapter 5
Habitat subdivision	Subdivision of a single large area of habitat into several smaller areas	Chapter 6
Habitat isolation	The isolation of habitat areas for a given species—the opposite of habitat connectivity	Chapter 6
Habitat connectivity	The connectedness of habitat patches for a ...

Table of contents

• About Island Press
• Title Page
• Copyright Page
• Table of Contents
• Dedication
• Acknowledgments
• Preface
• CHAPTER 1 - Introduction
• PART I - Landscape Change: An Overview
• PART II - The Species Perspective: Key Processes Affecting Individual Species
• PART III - The Human Perspective: Landscape Patterns and Species Assemblages
• CHAPTER 11 - Edge Effects
• PART IV - Studying Species and Assemblages in Modified Landscapes
• PART V - Mitigating the Negative Effects of Landscape Change on Species and Assemblages
• PART VI - Synthesis
• About the Authors
• References
• Index
• Island Press Board of Directors