The Impact of Global Climate Change on Tropical Forest Biodiversity in Amazonia

Species’ ranges are configured according to their tolerance of environmental conditions, especially climate, and their history of dispersal since speciation. Previous studies of the potential impact of climate change on biodiversity have been biased towards species of high latitudes. This situation results from a lack of detailed knowledge about the distribution of tropical biodiversity, and from the smaller degree of warming expected at low latitudes. However, various General Circulation Models (GCMs) simulate regional drying and increasing seasonality for parts of the tropics, including Amazonia. This may have a greater impact on tropical forest flora than temperature change alone. The Amazon region holds a high proportion of global biodiversity, yet conservation plans rarely consider possible climate change impacts. This thesis presents a methodology for projecting a set of Amazonian plant species’ ranges from limited data, and estimating their response to climate change scenarios. Species are classified into plant functional types (PFTs), which share traits such as growth form and reproductive strategy. Species' current distributions are modelled over a coarse scale (a 1º latitude-longitude grid), using a suitability index based on bioclimate variables. Distributions are additionally limited by species’ absolute tolerances to extreme values, and by dispersal barriers. A sizestructured population is simulated for each cell, to enable modelling of lags in response to climate change. In the standard impact scenario (SIS), future population processes are simulated over 100 years, with changes in the variables governing cell suitability being applied annually according to anomalies from a selected GCM. The run is repeated for each species using anomalies of half that magnitude, as a reduced-impact scenario (RIS). The range of potential outcomes for each species and PFT is evaluated. Widespread impacts are seen under both scenarios. An alternative impact scenario (AIS) is devised to examine the effects of allowing some "c-species" to thrive under heightened AET. The most vulnerable taxonomic groups, PFTs and geographical regions are identified as targets for monitoring and conservation action. In particular, there is a dramatic loss of species' viability in much of northeastern Amazonia at 2095 under all scenarios. The far western part of Amazonia is identified as important for persistence of the greatest number of species. Areas falling between the major rivers of the region have very limited distribution data, so are highlighted for future biodiversity survey work.