Elsevier

Biological Conservation

Volume 112, Issues 1–2, July–August 2003, Pages 87-97
Biological Conservation

Developing regional and species-level assessments of climate change impacts on biodiversity in the Cape Floristic Region

https://doi.org/10.1016/S0006-3207(02)00414-7Get rights and content

Abstract

We assess the potential impact of climate change on plant diversity in the Cape Floristic Region (CFR) and its interaction with land transformation that has already occurred in the region. Predictions were made both at the scale of the Fynbos Biome (the dominant vegetation assemblage in the CFR) and for selected Proteaceae species. Bioclimatic modelling identified parts of the biome at particular risk from climate change. Species-level modelling (Generalised Additive Modelling) was done for 28 Proteaceae species selected from areas at high risk of biome loss, revealing individualistic range changes in a pattern broadly consistent with biome modelling results. Most species experienced potential range contractions (17 of 28), of which five showed range elimination. Several species (11 of 28) showed potential range expansions. For species showing range contractions, current land transformation had less impact on future potential ranges than did climate change, because many species ranges shifted to higher altitudes where land transformation is currently less prevalent. Fewer than half of the high-risk species showed overlap between current and future potential range, showing that propagule transport, establishment of species in novel ranges and conservation of landscape linkages will be critical for maintenance of biodiversity. Methods described here provide useful forecasts of potential climate change impacts that could guide conservation responses, but results need cautious interpretation in the light of the many assumptions underlying the techniques used.

Introduction

Recently documented biotic responses to possible human-induced climate change (Hughes, 2000, Peterson et al., 2002) raise a crucial question for conservationists: Are projected climate changes likely to be a threat to the conservation of biodiversity? Conservation efforts have generally assumed that climate is a constant feature of the environment, and that species distributions are effectively constant in space and time (Cowling, 1999). Both the former and latter assumptions are unjustifiable, as it is now well understood that the earth's climate has changed significantly and rapidly on time scales of decades to millennia (Broecker, 1999, Zachos et al., 2001); that species have shifted their ranges as climate has changed (Hewitt, 2000, Huntley and Birks, 1983, Parmesan, 1996, Parmesan et al., 1999); and that these range shifts are often individualistic responses to climate change (Graham and Grimm, 1990, Warren et al., 2001) as opposed to wholesale migrations of ecosystems or biomes. Several authors have begun to explore how conservation plans can begin to assess this threat and incorporate these insights into strategies that will be robust to climate change (e.g. Halpin, 1997, Hannah et al., 2002), and some planning to accommodate climate change impacts has been developed for the CFR (Cowling and Pressey, 2001, Cowling et al., in press, Rouget et al., in press) and for the winter rainfall Succulent Karoo Biome of South Africa (Cowling et al., 1999a). Nonetheless, explicit adaptations to conservation planning in the face of climate change are in their infancy.

The CFR boasts an exceptionally rich flora with high levels of endemism (Cowling et al., 1989), that may result, in part, from a unique climate and climate history (Cowling et al., 1998, Midgley et al., 2001). The mediterranean-type climate of the CFR may now be changing, characterised by increasing temperatures and reduced rainfall, especially in winter months (Tyson et al., 2002, Wand et al., submitted for publication). Conservation planning for the region has just begun to account for these significant changes and the impact they may have in concert with other threats (Cowling and Pressey, 2001, Cowling et al., in press, Rouget et al., in press).

If species range shifts are the likely dominant species response to future climate change, then spatially explicit planning will be fundamental to estimating the rate and direction of species movements required to ensure retention of sufficient range for their persistence. Modelling can help inform efforts to place land under effective conservation management, either in formally protected areas or in unprotected areas suitable as habitat. These tools must be relevant at regional and even sub-regional scales—the scales at which most practical conservation decisions, such as land acquisitions, are made.

In this paper, we develop a biome- and a species-based approach to assessing the regional impacts of climate change on the future distribution of a major floristic group (Proteaceae). We address a number of questions:

  • 1.

    What biome-level patterns may be expected under future climate change, and what are the comparative potential range shifts in representatives of a dominant taxon, the Proteaceae, in areas of potential biome contraction?

  • 2.

    How much has land transformation constrained the potential migration of species in response to climate change?

  • 3.

    What proportion of species are under severe threat of extinction under the projected climate change scenarios?

  • 4.

    What are the implications of these patterns for conservation planning?

Section snippets

Study area and selected species

We modelled the Fynbos Biome (sensu Rutherford and Westfall, 1994) and selected endemic members of the family Proteaceae within the CFR. The Fynbos Biome is the dominant biome within the Cape Floristic Region. We focused attention on the western parts of the CFR, having established large potential impacts of climate change in this region (Midgley et al., 2003). The study area includes much of the western Cape (between 33–35° S and 18–22° E), a region that has a Mediterranean-type climate with

Regional-level assessment

Biome-level modelling shows that the Fynbos Biome stands to lose significant areas near its northerly (equatorward) limits, especially in the coastal forelands and inland plains along the west coast (see Fig. 1) in response to projected climate change. The biome envelope suggests future contraction southwards onto the mountains of the Cape Fold Belt. Plains and slopes at lower altitudes along the west coast and northern borders of this mountain belt do not retain suitable bioclimates for

Acknowledgments

We acknowledge with thanks comprehensive funding from the Centre for Applied Biodiversity Science, Conservation International, Washington, DC, and helpful and constructive comments from Richard Cowling and Bob Pressey on an earlier draft of this paper.

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