Document: GRE-3-34-30

Dendroecology of Pinus ponderosa in the Okanogan National Forest, WA.

KUSNIERCYZK, E.* and G.ETTL

St. Joseph's University, Philadelphia, PA 19131 USA ¹

Abstract:
The growth response of Pinus ponderosa to climate was assessed at 4 elevations from low-elevation treeline (i.e. steppe-forest ecotone850m) to its high-elevation limit (1500m, where it grows in mixed stands with Psuedotsuga menziesii) on 3 different mountains in the Okanogan National Forest, WA. Principal component analysis indicates the twelve mean site chronologies are similar in most respects (PC1=82%). Growth-climate relationships were determined among mean site chronologies and monthly mean temperatures, and total precipitation in the current and previous hydrologic year, using partial correlation analysis. Growth is negatively correlated with June temperature, and positively correlated with previous July and September precipitation on the majority of sites. Growth is also positively correlated with November temperature on the middle, low, and steppe sites. Finally, winter precipitation is positively correlated with the majority of steppe sites. Ponderosa pine growth is primarily limited by water availability across its elevation range. Positive correlations with previous September precipitation and November temperature at all but the high elevation sites suggest that carbon stored during the fall is important for growth in the following year. Positive correlations between winter precipitation (i.e., snow) and growth indicate that winter snowpack may be important in recharging soil moisture in the spring, thereby maintaining ponderosa pine at the steppe ecotone. If climate becomes warmer and drier, then ponderosa pine will grow more slowly across its elevation range in the eastern Cascades. In contrast, warmer and wetter conditions would result in increased growth, however these conditions may result in decreased growth at low elevation treeline due to decreased snowfall (i.e. a switch from snow to rain).

Keywords: Dendrochronology, ponderosa pine, climate change

This abstract is being presented at: 3:30 PM in session:
CLIMATE CHANGE