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Quantifying Terrestrial Habitat Loss and Fragmentation: a Protocol

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Quantifying Terrestrial Habitat Loss and Fragmentation: a Protocol 12 August, 2005 Kevin McGarigal Department of Natural Resources Conservation University of Massachusetts 304 Holdsworth Natural Resources Center Box 34210 Amherst, MA 01003 (413)545-4358 Fax (413)577-0655 Phone Quantifying Terrestrial Habitat Loss and Fragmentation: A Protocol Kevin McGarigal Natural Resources Conservation Department, University of Massachusetts, Amherst, MA 01003. Email: [email protected] Sam Cushman USDA Forest Service, Rocky Mountain Research Station, Missoula, MT 59807. Email: [email protected] Claudia Regan USDA Forest Service, Rocky Mountain Region,, Denver, CO. Email: [email protected] Fragmentation Protocol ii Abstract Anthropogenic habitat loss and fragmentation have been implicated as among the key drivers of the burgeoning global biodiversity crisis. In response, there is a growing mandate among natural resource managers to evaluate the impacts of proposed management actions on the extent and fragmentation of habitats. Unfortunately, few guidelines exist to help managers understand the many complex issues involved in the quantitative assessment of habitat loss and fragmentation. In our Primer, we explore habitat fragmentation as a landscape-level process in which a specific habitat is progressively sub-divided into smaller, geometrically altered, and more isolated fragments as a result of both natural and human activities. We describe alternative perspectives on fragmentation in which habitat patches are viewed either as analogs of oceanic islands embedded in an ecologically neutral sea or as patches of variable quality embedded within a complex and heterogeneous mosaic of patches of varying suitability and affects on habitat connectivity. In the conventional island biogeographic perspective, habitat loss and fragmentation is described as a landscape transformation process involving several recognizable phases that are demarcated by significant changes in the pattern or function of the landscape. We describe the key spatial components of habitat loss and fragmentation: habitat extent, subdivision, geometry, isolation, and connectivity, and their affects on individual behavior and habitat use, population structure and viability, and interspecific interactions. Finally, we view the evidence, both theoretical and empirical, regarding the issue of when is habitat fragmentation important, and conclude that it depends not only on the pattern of habitat distribution but on the life history characteristics (e.g., dispersal capabilities) of the target organism(s). The Primer on habitat fragmentation provides the foundation for examining several key issues in the analysis of habitat loss and fragmentation. First, what constitutes habitat. Second, how do we represent landscape structure in a digital data model. Third, what are the components of habitat loss and fragmentation. Fourth, what is the appropriate scale of analysis, Fifth, what is the relevant spatiotemporal context for assessing habitat loss and fragmentation. Finally, how are habitat loss and fragmentation measured. The conceptual overview (i.e., Primer) on habitat fragmentation and discussion of important analytical issues provides the foundation for a step-by-step protocol for quantitatively assessing habitat loss and fragmentation. This protocol consists of five steps and is intended to serve as a general guideline for the quantitative assessment process, but one that must be tailored to meet the specific conditions of any particular application. Fragmentation Protocol 1 TABLE OF CONTENTS PURPOSE AND ORGANIZATION ...............................................1 A PRIMER ON HABITAT FRAGMENTATION ....................................3 What is Habitat Fragmentation? ...............................................3 Habitat Fragmentation Paradigms..............................................7 Static Island Biogeographic Model ..........................................7 Dynamic Landscape Mosaic Model .........................................10 Spatial Components of Habitat Fragmentation ...................................11 Biological Consequences of Habitat Fragmentation...............................14 Individual Behavior and Habitat Use .......................................15 Population Structure and Viability .........................................23 Interspecific Interactions .................................................28 When is Habitat Fragmentation Important?......................................29 Implications for National Forest Management ...................................31 ISSUES IN THE QUANTITATIVE ANALYSIS OF HABITAT LOSS AND FRAGMENTATION..........................................................34 What is the Appropriate Model of Landscape Structure?...........................34 What is the Appropriate Scale of Analysis? .....................................36 What is the Relevant Spatiotemporal Context for Assessing Habitat Loss and Fragmentation? .....................................................................39 What are the Best Measures of Habitat Loss and Fragmentation? ....................40 A PROTOCOL FOR ASSESSING HABITAT LOSS AND FRAGMENTATION ..........49 Illustrated Example .....................................................49 Step 1: Establish Analysis Objectives..........................................51 Illustrated Example .....................................................52 Step 2: Define the Landscape ................................................53 Illustrated Example .....................................................55 Step 3: Establish a Spatio-Temporal Reference Framework.........................57 Illustrated Example .....................................................58 Step 4: Quantify Habitat Fragmentation ........................................61 Illustrated Example .....................................................61 Step 5: Characterize the Landscape Relative to Analysis Objectives..................68 Illustrated Example .....................................................69 ACKNOWLEDGMENTS ......................................................71 LITERATURE CITED ........................................................72 FIGURE CAPTIONS.........................................................110 Fragmentation Protocol 2 PURPOSE AND ORGANIZATION Many scientists believe that the earth is facing a mass extinction (Lawton and May 1995, Vitousek et al. 1997, Wilson 1999, Myers and Knoll 2001, Balmford et al. 2003). Current global extinction rates for animals and plants are as much as 1,000 times higher than the background rate in the fossil record (Wilson 1999) and vertebrate animal taxa are disappearing at disproportionately high rates (Baillie et al. 2004). Anthropogenic habitat loss and fragmentation have been implicated as among the key drivers of this global biodiversity crisis (Wilcox and Murphy 1985, Saunders et al. 1991, Andren 1994, Myers and Knoll 2001, Balmford et al. 2003). In response, there is a growing mandate for natural resource managers to evaluate the impacts of proposed management actions on the extent and fragmentation of habitats (Fahrig and Merriam 1985, Lubchenco et al. 1991, Hobbs 1993). For example, habitat fragmentation is currently listed by the Chief of the Forest Service as one of the "four threats" of greatest concern in management of National Forest Lands. Unfortunately, few guidelines exist to help managers understand the many complex issues involved in the quantitative assessment of habitat loss and fragmentation. The main purpose of this document is to describe a protocol for quantitatively assessing terrestrial habitat loss and fragmentation. While the theoretical framework and concepts presented here are broadly applicable to any ecological system, the focus here is on terrestrial habitats in forested landscapes of North America. The motivation for this document, in part, stemmed from two regional conferences on forest fragmentation. The first conference entitled "Forest Fragmentation: Wildlife and Management Implications" was held in Portland, Oregon on 18-19 November, 1998. The conference was convened to provide a synthesis of the current state of knowledge related to fragmentation in managed forests of the Pacific Northwest and resulted in an edited book (Rochelle et al. 1999). The second conference entitled "Forest Fragmentation in the Southern Rocky Mountains" was held in Fort Collins, Colorado on ??-?? ??, 1999. The conference was similarly convened to provide a synthesis of the current state of knowledge related to fragmentation in forests of the southern Rocky Mountains and also resulted in an edited book (Knight et al. 2000). While the material presented at these conferences and in the subsequent books clearly demonstrated the rapid growth in our scientific understanding of fragmentation, it was clear that managers lack clear guidelines for implementing these scientific principles. The purpose of this document is to help bridge that gap between science and management in regard to habitat loss and fragmentation. This document is organized into three major sections. The first section provides a primer on habitat fragmentation. Specifically, what is habitat fragmentation, what causes it, why it is important, and when does it matter? An understanding of the concepts presented in this section is prerequisite to full comprehension and appreciation of the material presented in the subsequent sections. The second section discusses several key issues in the analysis of habitat loss and fragmentation. Specifically, what constitutes
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