"A model for tree migration constrained by palaeoecological data"Robson, DominicA model for tree migration constrained by palaeoecological data Dominic T. Robson, I. Colin Prentice, Sandy P. Harrison It is well established that human-driven climate change will cause shifts in the geographical ranges of climates suitable for particular species. The IPCC Fifth Assessment Report concluded that the observed recent migration rate of many tree species will not allow them to keep pace with the anticipated changes. However, pollen records for many European tree species suggest migrations during the last deglaciation and early Holocene occurred much faster than implied by recent observations. While most seeds are only dispersed over short distances from a parent tree, the palaeo-record implies that even very rare occurrences of long-range dispersal play a much greater role in driving the overall migration. The rarity of these long-distance events and the impossibility of tracking every seed which is carried away by animals, birds, or strong winds mean that neither their likelihood nor distance-dependence can be constrained by direct observation. To resolve this issue, we have constructed a model designed to predict the migration of European tree species during the deglaciation and the Holocene. As in most existing models of tree migration, we use a mixed dispersal kernel whereby the majority of seeds are dispersed locally and only a few get transported over a long distance. However, unlike existing models, we do not fix the dispersal kernel a priori but optimize its parameters to reproduce the observed migration history of each species. Treatments of both interspecific and intraspecific competition are included and are necessary to explain why some species were unable to migrate into regions which were otherwise climatically suitable. By training this model using palaeodata, we are able to provide observational constraints on dispersal, allowing for more realistic simulations of the potential for tree species migration under future climate change. |
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