Systematic reviewEffectiveness of terrestrial protected areas in reducing habitat loss and population declines
Introduction
Protected Areas (PAs) have long been regarded as an important tool for maintaining habitat integrity and species diversity (Brooks et al., 2004, Butchart et al., 2010, Coad et al., 2008, Rodrigues et al., 2004), covering more than 12.7% of the planet’s land surface (Bertzky et al., 2012). However, there is considerable debate on the extent to which PAs deliver conservation outcomes in terms of habitat and species protection (Brooks et al., 2006, Ferraro and Simpson, 2002, Meir et al., 2004). It has been suggested that many of the world’s PAs exist only as ‘paper parks’ (Dudley and Stolton, 1999), lacking effective management capacity, and unlikely to deliver effective conservation (Joppa et al., 2008).
PAs are often treated as a single conservation strategy. However, in reality they are established for a variety of reasons, with very different objectives and criteria for success. PAs have been set up for the conservation of ecosystems and their constituent species (Dudley, 2008), protection of specific threatened species (Liu et al., 2001), ecosystem services (Campos and Nepstad, 2006), or for cultural and social reasons (Coad et al., 2008). Understanding the conditions under which PAs deliver conservation benefits for habitats and species is essential for policy makers, managers and conservation advocates (Brooks et al., 2004, Kleiman et al., 2000, Margules and Pressey, 2000).
The success of PAs has generally been evaluated using measures such as the representativeness of PA networks in terms of their species diversity, or coverage of endemic and threatened species (Rodrigues et al., 2004), assuming that PAs provide effective protection once established. Alternatively, by investigating management ‘inputs’ – e.g. whether PAs have management plans, boundaries, staffing, and other management systems and processes (Jachmann, 2008), assuming that increased levels of management equates to successful protection. However, these analyses are not able to describe how conditions inside PAs change over time (Craigie et al., 2010), or evaluate the effectiveness of protection, by combining measures of inputs and measures of outcomes in a temporal framework; thus measuring how biodiversity outcomes change over time in relation to protection or implementation of management actions.
The objective of this paper is to use a ‘systematic review’ methodology (Pullin and Knight, 2009) to review the evidence that PAs deliver a positive change in two conservation outcomes: (a) habitat cover and (b) species populations, i.e. the ability of PAs to maintain or improve native habitat integrity, or native species populations, over time respectively. We further consider the impact of different PA management interventions, or characteristics, where measured, on biodiversity outcomes.
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Search strategy
To locate relevant literature, we searched 14 databases, eight specialist sources and 13 websites in English (Table S1). We identified a list of relevant search terms and used Boolean operators and multi term searches (Table S2). Anonymous reviewers appraised the list of relevant search terms and the search strategy. The search was conducted between July and August 2010, covering all publications available up to that point. For a full description of the search strategy, search-terms, and
Results
Of the 2599 publications selected through the systematic search strategy, we found 51 publications on habitat cover and 35 publications on species population trends that fulfilled the inclusion criteria.
Within 13 of the 51 habitat change publications there were multiple counterfactual scenarios. When separated these yielded a total of 76 studies. Three population trend publications covered more than one evaluation of PA effectiveness, yielding 42 studies in total across the 35 publications.
Discussion
This review highlights the limited availability of evidence on the impact of PAs on habitats and fauna. Further, and more alarmingly, there is very little quantitative understanding of how, and under what conditions various PA management interventions improve PA effectiveness.
Analysis of 76 studies across local, regional, and global scales indicates that PAs experience lower rates of habitat loss than areas that are not protected. However, the majority of habitat studies suggest that the effect
Acknowledgements
We thank Professor A. Pullin and the Collaboration for Environmental Evidence for handling the systematic review, and the five reviewers, especially Dr. D. Dawson for invaluable feedback on the original manuscript. We also thank the three anonymous reviewers of this manuscript for valuable contributions and suggestions.
We thank the Danish National Research Foundation for financial support. We also thank the IUCN SSC/WCPA Joint Task-Force on Biodiversity and Protected Areas, UNEP–WCMC, WWF, and
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