Modelling spread of British wind-dispersed plants under future wind speeds in a changing climate.
Climate change impacts on habitat suitability and demography are often studied, but direct effects on plant dispersal are rarely considered. To address this we analysed climate model projections of future wind speeds and modelled their possible impacts on dispersal and spread of wind-dispersed plants. Projections for 17 Global Climate Models and three emission scenarios suggested great uncertainty about wind speeds in southern England by the period 2070-99. Projections ranged from -90% to +100% change in the mean wind speed, although the average projection was for large falls in both summer and winter wind speeds. Using a novel method for converting projected changes in mean wind speed to new seasonal wind speed distributions, we parameterized a mechanistic model of seed dispersal by wind using baseline and changes in mean wind speed from -80% to +80%. The mechanistic seed dispersal model was combined with demographic data in an analytical model of plant spread. This was carried out for three British native and three non-native species, which represented a range of life-forms. Dispersal kernels and population spread rates were affected disproportionately by changes in wind speed, demonstrating nonlinear propagation of uncertainty in wind speed projections through to modelled plant spread rates. Sensitivity analyses showed differences among the plant species in which demographic transitions were most important in determining spread rates. By contrast, sensitivity of spread rates to dispersal parameters showed great consistency among species, with seed release height being more important than seed terminal velocity. Synthesis. Plant populations will need to shift their geographic ranges to keep pace with climate change-driven habitat loss. This study shows that climate change may affect that ability by decreasing the dispersal distances of wind-dispersed plants and thus their potential spread rates. However, the modelling approach presented here illustrates that uncertainty in climate models leads to an even greater uncertainty about how dispersal and spread will change in future climates. Caution should therefore be exercised in making predictions as to how fast plant species may spread in response to climate change.