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.