The Role of Topoclimate in Explaining Abrupt Growth Thresholds of Bristlecone Pine in the White Mountains of California, USA

Tuesday, 16 December 2014: 10:35 AM
Andrew G Bunn1, Matthew W Salzer2, Evan R Larson3, Stuart B Weiss4 and Malcolm K Hughes2, (1)Western Washington University, Environmental Sciences, Bellingham, WA, United States, (2)University of Arizona, Tucson, AZ, United States, (3)University of Wisconsin Platteville, Platteville, WI, United States, (4)Creekside Center for Earth Observation, Menlo Park, CA, United States
We present data on growth of approximately 100 individual bristlecone pine (Pinus longaeva) trees situated at and near upper treeline in the White Mountains of California. Most trees growing at treeline show positive trends in growth in the 20th century and vary with temperature at both decadal and interannual timescales. However, many trees situated just 50 m or more below treeline have growth patterns that do not correlate strongly with the trees from the highest elevations. Some of these growth disparities can be explained by understanding the role of topography (including nighttime cold air pooling) at the scale of tens of meters. In particular, trees growing below treeline but in the coldest locations of the hillslope track temperature variations. Conversely, the fast growth of some of the highest trees in the warmest biophysical settings has declined since the mid-1980s. This might suggest that the climate response of trees has recently shifted from being positively to negatively associated with temperature.