Model Refinements and Uncertainties

Further refinements in the plant-climate model can be achieved by integrating knowledge from molecular and quantitative genetics. An important point is that this model currently utilizes ground-truthed locations for the entire distribution of each species for current and future predictions, ignoring genetic adaptation to local/regional climate. This model assumes that each climate-adapted population will be able to occupy its climate space in the future regardless of the geographic distance. For example, it is clear that the Sierra Nevada metapopulation of western white pine is genetically different and occupies a climate that is different from western white pine in the more northern latitudes. However, it is unclear where the populations occupying current climate space in Sierra Nevada may move in the future. Future plant-climate model improvements should be able to correlate climate variables and genetic data. Ongoing studies are focused on the delimiting population-based adaptive traits and refining molecular genetic data from western white pine populations to project suitable climates for these populations under current and future climate scenarios. Similar studies can be conducted with whitebark pine and other tree species, but this will require investing in efforts to conduct thorough, rangewide genetic studies.

Most uncertainty in the plant-climate model is associated with future climate scenarios and the GCMs. Precipitation is a major factor for predicting suitable climate space of plant species. For the Western United States and Canada, models display consistency for increased winter precipitation; however, summer precipitation predictions remain inconsistent (IPCC 2001). In addition, the time scale between loss of suitable climatic space and extirpation of local populations remains uncertain. Much of this uncertainty comes from site-specific biotic interactions. For example, two potential scenarios can be envisioned: (1) Slow attrition from succession where whitebark pine persists for decades or (2) stress from maladaptation leading to insect, (e.g., bark beetle) outbreaks or disease, (e.g., root rots) epidemics resulting in local extirpation within years. Projected scenarios are further complicated by mortality and loss of cone crops to white pine blister rust and insect attack. Continued studies are needed to address these uncertainties and improve predictions of climate-change impacts on distribution and population genetic structure of whitebark pine and western white pine.