Paleoecology of a modern Pinus albicaulis population in Grand Teton National Park, WY
Whitebark pine (Pinus albicaulis) is a critically threatened North American conifer. In modern times, it has experienced a significant decline in population due to pine beetle infestations, blister rust infections, fire suppression, and climate change. While climate, fire, and vegetation are strongly linked on regional and global scales, the relative roles of these three factors are not well-documented during the Holocene in high elevation mountain sites of North America. Recent anthropogenic changes in climate and fire management practices are underway, but the potential responses of subalpine vegetation to these environmental changes remain relatively unknown. We documented the paleoecology of an unnamed, high-altitude pond whose watershed contains a large number of P. albicaulis trees located at 2805m elevation in Grand Teton National Park, U.S.A. Using a 1.5 meter lacustrine sediment core collected in 2010, we generated a Holocene-scale fire and vegetation record using fossil pollen, charcoal, and macrofossils preserved within the core. We also conducted a dendrochronological study of the current stand of P. albicaulis in the watershed to determine both approximate dates of establishment and responses to past climate change of this modern stand.
Sedimentary charcoal data indicate significant variability in both fire frequency and fire intensity during the Holocene. Fire frequency ranges from 10 to 60 fire episodes/1000 y identified with charcoal peaks above background charcoal in the statistical program CHAR. Charcoal data further indicate that fire frequency is decreasing, while intensity is increasing toward present. Sedimentary pollen data suggest the study site has been primarily dominated by P. albicaulis until the last 1000 years, with brief periods of vegetation dominated by non-arboreal taxa that indicate the presence of either successional dynamics or shifts in treeline location. Ages of individual P. albicaulis trees living in the watershed today average 365 years. Growth of the individuals in the current stand, as indicated by ring widths, has been declining since 1949. This decrease in tree annual growth is correlated temporally with decreased growing season temperature ranges driven by a warming climate. These results indicate that current populations of P. albicaulis in the western U.S. are undergoing large ecological changes due to recent shifts in climatic conditions and fire regimes. Management of subalpine conifer ecosystems should include long-term paleoecological data to inform decisions about suitable habitat and fire management.