Status Of The Whitebark Pine Pinus Albicaulis In Alberta PDF Download

Understanding the regeneration stage of any species is key to determining the processes that lead to population persistence and structure, community development, and succession. In the case of the endangered whitebark pine (Pinus albicaulis), knowledge of regeneration processes will be important for developing approaches for recovery and restoration of the species. I investigated biophysical drivers of whitebark pine seedling presence, abundance, and growth in the northern Alberta Rocky Mountains where mortality from white pine blister rust (caused by the fungus Cronartium ribicola) and mountain pine beetle (Dendroctonus ponderosae) remains low and whitebark pine regeneration is poorly studied. Transects were established in different mesohabitats (community type and elevation) to determine how these factors influence whitebark pine regeneration. Mesohabitat-scale conditions and seedling density along each transect were measured and microsites with and without whitebark pine seedlings were characterized along each transect. The height, age and health of each whitebark pine seedling found in each microsite was recorded and a subset of seedlings was destructively sampled in order to analyze annual growth and release. In forest mesohabitats canopy gaps at microsite scales favored occurrence, growth rate and growth release. However, at the mesohabitat scale seedling abundance was positively related to canopy cover. Whitebark pine seedlings in open habitats below treeline were negatively associated with cover of rock, graminoids and seedlings of other tree species, grew fastest at intermediate values of temperature and dryness, and exhibited release in microsites with little other understory cover. These results suggest that at the northern portion of its range, whitebark pine grows best in conditions that limit competitors but still allow for sufficient growth. This contrasted with the situation in alpine and treeline mesohabitats, where increased growth rates, growth release and seedling presence were associated with warmer microsites that had higher vegetation cover. Seedling density in both open and treeline environments was highest along southwest facing slopes. That release and general success of seedlings was better in canopy gaps supports the use of restoration activities such as thinning overstory trees and planting in open mesohabitats or microsites. As the regeneration niche of whitebark pine differed among mesohabitats and biophysical drivers of success differed among presence, abundance and growth of whitebark pine, I suggest that it is critically important to consider the mesohabitat and all factors of regeneration success when restoring whitebark pine.