Anthropogenic climate change poses a threat to biodiversity across the globe. One of the most important responses for a species that is sensitive to climate is migration and a shift in species distributions across a landscape. In mountainous landscapes, fine-scale variation in topography (south vs. north-facing slopes, cold air drainages, etc.) can generate a wide range of climate conditions over a fairly small spatial scale. This variability may allow plants and animals to respond to global climate change through local shifts in distribution, providing spatial resilience in the face of temporally changing conditions. This project will examine the influence of topography on microclimate and plant distributions in Table Mountain National Park, part of the mega-diverse Cape Floristic Region of South Africa. Distributions of shrubs in the Proteaceae will be examined in relation to fine-scale topographic variation at a 30m pixel scale. A detailed study of diurnal and seasonal temperature variation will be conducted to quantify elevational lapse rates, the occurrence of marine inversion layers, and the small-scale effects of slope, aspect and cold air drainage. The results will be used to develop a spatial model of topoclimate and to refine statistical models of plant distributions in relation to climate. Finally, future climate scenarios will be downscaled to a fine spatial scale, and combined with species distribution models to test the hypothesis that topoclimatic heterogeneity will enhance population persistence in the face of climate change.

In connection with the proposed research, the PI will teach a two-week short course for South African graduate students on statistical methods in spatial analysis and phylogenetics. Participation by students from underrepresented economic and ethnic groups will be encouraged. The workshop will contribute to development of statistical expertise and the professional careers of participating students, and build a foundation for continuing international collaboration.

Project Report

Conservation of biodiversity faces increases threats due to anthropogenic climate change. In mountain environments, species are expected to shift uphill in response to rising temperatures, and eventually face the threat of extinction when they run out of room to migrate further. One factor that could ameliorate this threat is the existence of ‘topoclimate’ variation (small scale climate variation caused by differences in solar exposure, pooling of cold air in valleys, etc.) which may create local refugia in montane environments. In this project we quantified the extent of this variation by monitoring temperature and humidity at almost 100 stations across a heterogeneous landscape in Table Mt. National Park, South Africa (a biodiversity hotspot). As expected we found highly significant effects of topography on local climate, especially due to effects of cold air pooling on minimum temperatures and effects of solar exposure on maximum temperatures (in addition to the effects of elevation). We also studied the distribution of a number of tree species, and examined distribution patterns in relation to climate. Based on statistical models of distributions for one local endemic species (Leucadendron strobilinum) we found that this topographic heterogeneity will buffer the impacts of climate change, allowing survival with up to 3°C of warming rather than only 2°C that we would have predicted without considering fine scale heterogeneity. These results support the view that conservation of high levels of geodiversity (e.g. diversity of soils, topography, etc.) is a strategy that is likely to enhance species survival in the face of climate change. However, it is important to note that these local effects do not protect species indefinitely, and rapid climate change is expected to eventually impact the distribution and survival of many species, as in our example from this study.

National Science Foundation (NSF)
Division of Environmental Biology (DEB)
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Alan James Tessier
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University of California Berkeley
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