A bioclimatic model for the distribution of Sphagnum-dominated peatlands in North America under present climatic conditions

Aim A model was developed that estimates the climatic and geographical dist ribution of Sphagnum-dominated peatlands in western Canada and North Americ a. Location The model is based on the abundance of Sphagnum species on 640 pea tland sites located in proximity to permanent weather stations throughout w estern Canada. Methods The per cent cover of Sphagnum species was quantified for all possi ble combinations of mean-annual temperature (MAT) and mean annual total pre cipitation (MATP) found in western Canada. Abundance values were expanded t o include all climatic values in North America, by interpolating within the matrix of values for western Canada using distance-weighted means. Because Sphagnum-dominated peatlands do not occur in areas having summer moisture index (P-PET) values less than or equal to 6 cm, that value was also includ ed in the model. The result produced a matrix of 3360 grid nodes in which e ach node was characterized by MAT, MATP and P-PET values and the presence o f Sphagnum-dominated peatlands. The climatic data in the model was then mat ch merged with the MAT, MATP and P-PET values obtained from Leemans & Crame r (The IIASA Database for Mean Monthly Values of Temperature, Precipitation , and Cloudiness on a Global Terrestrial Grid. International Institute for Systems Analysis, Laxenberg, 1991), which is a global data set that also co ntains geographical data on a 0.5 degrees latitude by longitude grid. The g eographical distribution of Sphagnum-dominated peatlands was then mapped fo r western Canada and North America. Those maps were compared with the obser ved distribution of bogs and poor fens for the same area. Results Results of the comparisons indicated that the model's estimations m atched the southern distribution of Sphagnum-dominated peatlands relatively closely. Results for the northern distribution, however, were not as accur ate. The overall accuracy was c. 80%. Main conclusions Some of the errors were caused by inaccurate climatic data which resulted from the lack of permanent weather stations in northern are as and the lack of definition of the northern limits of the actual distribu tion of bogs and poor fens. In areas where both the climatic data and the a ctual distribution of Sphagnum-dominated peatlands are accurate, the model accuracy was c. 90%.