How much do local factors matter for predicting transient ecosystem dynamics? Suggestions from permafrost formation in boreal peatlands

With rapid climate warming, ecosystems will probably exhibit complex dynami cs because local factors and life history attributes of species mediate the effects of regional climate change. To assess the relative importance of l ocal vs. regional processes on permafrost formation in boreal peatlands, I sampled for permafrost and factors affecting its formation in 38 collapse s cars across a 4 degrees C mean annual temperature (MAT) gradient in the dis continuous permafrost zone of northern Manitoba, Canada. Three complimentar y approaches were used to model factors important to permafrost formation a t both local and regional scales. In the first analysis, a mechanistic, spa tial model of permafrost formation was developed as a function of Picea mar iana size and proximity. In the second approach, permafrost formation was m odelled as a function of two local factors, diameter of Picea mariana trees and emergent organic matter depth, and the regional factor, mean annual te mperature (MAT). Finally, published aerial photography data were used to de termine whether the proportion of bogs with permafrost changes across a MAT gradient. Results show that permafrost formation in boreal permafrost peat lands is best described as a locally driven process within regional climati c constraints. At local scales of 1-2 meters, the spatial and size distribu tions of trees controlled the spatial distribution of permafrost. At region al scales, tree size was a significantly better predictor than emergent org anic matter or MAT. These results suggest that transient models of disconti nuous permafrost based only on climate may poorly predict changes in vegeta tion and permafrost.