The Biogeography of Biodiversity in Southern Africa

Understanding the distribution of speciesandpatterns of biodiversity across theearth is a central problem in ecology and biogeography. Key to insight into this problem is understanding how present, past and future climate may drive biotic patterns spatially and temporally. We propose developing Bayesian hierarchical modeling that willprovide a framework for synthesis and prediction by integrating pattern and process across multiple levels, from populations to regional climates. The world is in a dramatic phase of climate change that will drive potentially dramatic changes in species distribution patterns. Many scientists have pointed to a looming conservation crisis. Southern Africa provides a case study where this is especially true. Yet the tools currently at hand are inadequate in providing sufficient predictive power (and uncertainties thereof) with sufficient spatial resolution to understand, plan for and address the crisis. For more on this project, visit Dr. Silander's site.

Overview of my work in South Africa

The U.S. Global Change Research Program has recognized a need for understanding the potential consequences of climate variability and change on ecosystems (EPA, 2007).   Improved understanding of ecosystem processes, including phenology and disturbance, is an area of research identified by the scientific community as a priority for research by the U.S. Climate Change Science Program  (Lucier et al., 2006).   In that report, Lucier, et al. state that researchers have not yet comprehensively understood the ecological impacts of changes in phenology or frequencies and intensities of disturbance regimes that may result from global change, despite their ecological importance.  They also point out that we need better mechanistic understanding of ecosystem processes, including “interactions of ecosystems with the atmosphere, climate, and human activities.” Climate change is presenting managers and decision- makers with a new set of challenges for the conservation of the environment.  In addition to the ‘traditional’ environmental threats such as toxic pollution, habitat destruction, and invasive species, we are now faced with the challenge of changing environmental conditions at a global scale.

Phenology, the timing of ecological events, is an important indicator of ecosystem processes and can be used as a tool to understand the mechanisms behind ecosystem function.  Phenology has been shown to be important for the global carbon cycle (Keeling et al., 1996), inter-species competition (Rathcke and Lacey, 1985), and several other ecological phenomenon (Badeck et al., 2004).  Changes in phenology as a result of global climate change have been documented in all major terrestrial, marine, and freshwater groups (Parmesan, 2006).  In addition, the timing (frequency and seasonality) of wildfire has a profound ecological role in ecosystems ranging from dry tropical forests to Mediterranean chaparral and boreal forests (Adamson, 1935; Zedler et al., 1983; Booysen and Tainton, 1984; Clark, 1988; Bond, 1995).  Changes in fire regime due to recent climatic changes have also been reported (Westerling et al., 2006).  Fire can also be an important precursor of air pollutants thousands of kilometers away, making its understanding vital for air quality control  (Wotawa and Trainer, 2000).  Monitoring changes in phenology and fire regime and understanding the drivers of those changes will help researchers and managers to make more informed decisions about conservation and human well-being. 

Research into phenological change of this type demands the availability of extensive data and thus is limited to regions with somewhat complete records of temperature, precipitation, and ecological variables.  The Cape Floristic Region (CFR) of South Africa is uniquely an area of great ecological interest for which there exists abundant historical environmental data (Figure 1).  The CFR is an internationally recognized hotspot of floral biodiversity and is home to over 8,000 plant species, 69% of which are endemic (Goldblatt and Manning, 2000).  In contrast to other regions with high levels of biodiversity, such as the Amazon rain forest which is dominated by locally rare species with large ranges, the CFR species tend to be locally abundant but have small ranges and limited dispersal capabilities (Latimer et al., 2005).  These factors make the region’s flora vulnerable to decreased precipitation and shifts in the seasonality of precipitation predicted under future climate change (IPCC-WGII, 2001, Section 10.2.3.4).  In fact, bioclimatic models of species distributional shifts under the projected climate of 2050 predict a 51% to 65% reduction in the area of the fynbos, the Mediterranean climate shrub lands that currently dominate the region (Midgley et al., 2002).

Figure 1 : Map displaying the location of the Cape Floristic Region of South Africa

Fire is a critical ecological phenomenon that may be partly responsible for the CFR’s  high diversity (Cowling et al., 1994). Since various plant species have different strategies for responding to fire (some rely on seeds that require fire for germination, while others re-sprout from the rootstock), fire return time is an important determinant of the community makeup.  This is especially true along ecosystem margins, where other environmental conditions are favorable for two or more ecosystem types (Bond, 1983).  In addition, fire in the CFR is also a significant natural hazard that impacts the people living in the region.  For example, in the austral summer of 2000, unusually extensive fires burned over 18,000 ha in the Western Cape.  These fires damaged crops, destroyed over 270 residences on the Cape Peninsula alone, and resulted in an estimated $500 million in insurance claims.  The month prior to the fires was one of the driest on record and the preceding five days were extremely windy and near record high temperatures (~41oC) (Calvin and Wettlaufer, 2000).  Thus the societal impacts of fire can be significant.  A changing fire regime in that region could have major ecological (range shifts and changing community composition) and societal (risk to agriculture and residential areas) impacts.

However, projections of future change are difficult in the absence of a thorough understanding of how the biome has responded to climate change in the recent past.   Monitoring these phenological changes over time offers insight into how the changing climate is affecting plant communities.  In the CFR, important phenological events include the timing of germination and re-sprouting following fire, of annual growth flushes, flowering, seed set, and fire occurrence.   Despite its ecological importance, little phenological data has been collected with which to evaluate the presence and extent of phenological change in the ecosystems like the CFR.

Goal of the research

The overall goal of this project is to understand the dynamics of vegetation and fire in the landscape with respect to weather and climate in the recent past to inform our understanding of what may happen in the near future.  This includes the creation of new data and methods that will help the scientific and management community better understand ecosystem processes to inform the management of the complex environmental problems posed by climate change. The lessons learned in the CFR are likely to be useful for understanding other ecological systems, such as Californian chaparral and other Mediterranean regions.  Specifically, I plan to answer the following questions.

• To what extent is fynbos phenology, as measured by remote sensing and field observations, driven by temperature and precipitation across space and time?
• Have there been any trends in phenology in the recent past?
• To what extent is fire in the fynbos driven by temperature and precipitation?
• Are there perceivable trends in the occurrence of fire (i.e. are they becoming more frequent?)
• How might phenology and fire regime change under future climate projections