Document: DON-3-66-1

Recent growth in conifer species of western North America: Assessing regional and continental patterns.

MCKENZIE, D.*, A.E.HESSL and D.L.PETERSON

University of Washington, Seattle, WA 98195, USA ¹

Abstract:
We explored spatial patterns of low-frequency variability in radial tree growth among western North American conifer species and identified predictors (elevation, longitude, latitude, species) of the variability in these patterns. We selected 185 sites from the International Tree-Ring Data Bank (ITRDB), each of which contained 20-60 raw ring-width series. Using the raw ring-width series, we rebuilt two chronologies for each site using two conservative methods designed to retain any low-frequency variability potentially associated with recent environmental change. We used factor analysis to identify regional low-frequency patterns in site chronologies, and estimated the slope of the growth trend since 1850 at each site from a combination of linear regression and time-series techniques. This slope was the response variable in a regression-tree model to predict the effects of environmental gradients (latitudinal, maritime-continental, elevational) and species-level differences on growth trends. Between 18 and 32 of the 185 sites demonstrated a clear pattern of increasing growth between 1850-1980 A.D., depending on the standardization technique used. Pronounced growth increases are mostly associated with high-elevation sites (above 3000 m) and high latitude sites in maritime climates. Another 27 sites from the American Southwest demonstrated a synchrony with quasi-periodic patterns of drought. High-elevation and high-latitude sites are responding to changing environmental conditions and future research focused on these sites is necessary to identify the mechanisms responsible for directional changes in 20th century growth.

Keywords: long-term growth, Inernational Tree-Ring Data Bank, factor analysis

This abstract is being presented at: 3:15 PM in session:
Oral Session #66: Large Scale Climate Change.