Geographic clines in genetic variation

In risk mapping, the primary considerations are the presence of the host tree species, some measure of its density, and the distribution of the pest agent. High-density or overstocked stands are often considered to be of higher risk then stands with lower stocking levels; also important is the climatic stress on the population. This presentation shows how the predictions from a climate model can be converted to variables that may indicate the status of the stress of conifer species and their populations in the western USA and southwestern Canada. Forty-eight monthlies were derived from the basic temperature and precipitation data and fit to geographic surfaces with thin plate splines. These monthlies were then used to describe the clines of genetic variation that exist within species for growth characteristics. The mapping of clinal variation is useful in delineating seed zones and deriving seed transfer guidelines. The reverse image of such maps should indicate where the species would be under stress due to climatic conditions. For this reason, it is recommended that the monthlies and the climatic limits could be useful in risk mapping.