Global biome patterns of the Middle and Late Pleistocene

Our primary aim was to assess the hypothesis that distinctive features of
the patterns of vegetation change during successive Quaternary
glacial–interglacial cycles reflect climatic differences arising from
forcing differences. We addressed this hypothesis using 207 half-degree
resolution global biome pattern simulations, for time slices between
800 ka and 2 ka, made using the LPJ-GUESS dynamic global vegetation
model. Simulations were driven using ice-core atmospheric CO2
concentrations, Earth’s obliquity, and outputs from a pre-industrial and
206 palaeoclimate experiments; four additional simulations were driven
using projected future CO2 concentrations. Climate experiments were run
using HadCM3. Using a rule-based approach, above-ground biomass and leaf
area index of LPJ-GUESS plant functional types were used to infer each
grid cell’s biome. The hypothesis is supported by the palaeobiome
simulations. To enable comparisons with the climatic forcing, multivariate
analyses were performed of global vegetation pattern dissimilarities
between simulations. Results showed generally similar responses to
glacial–interglacial climatic variations during each cycle, although no
two interglacials or glacials had identical biome patterns. Atmospheric
CO2 concentration was the strongest driver of the dissimilarity
patterns. Dissimilarities relative to the time slice with the lowest
atmospheric CO2 concentration show the log–linear relationship to
atmospheric CO2 concentration expected of an index of ecocarbon
sensitivity. For each simulation, extent and total above-ground biomass of
each biome were calculated globally and for three longitudinal segments
corresponding to the major continental regions. Mean and minimum past
extents of forest biomes, notably Temperate Summergreen Forest, in the
three major continental regions strongly parallel relative tree
diversities, hence supporting the hypothesis that past biome extents
played an important role in determining present diversity. Albeit that
they reflect the climatic consequences only of the faster Earth system
components, simulated potential future biome patterns are unlike any
during the past 800 ky, and likely will continue to change markedly for
millennia if projected CO2 concentrations are realised.