Pacific yew (Taxus brevifolia Nutt.) growth and site factors in western Oregon
Liegel, Leon H.
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Conservation biologists in the Pacific Northwest have recently turned their attention to Pacific yew (Taxus brevifola Nutt.), given past harvest of this species for taxol and the fragmentation of late-successional forested landscapes. Understanding yew growth and reproduction patterns is important given interest in the long-term viability of yew populations and important contributions this species makes to stand structure. Our research, based on data from 11 intensively measured 2-ha plots, confirms and quantifies some early qualitative observations of yew tree size and age distributions in three forested subregions of western Oregon. These distributions show a general lack of regeneration in the last century, which should be of some concern to land managers given Pacific yew's contribution to late-successional stand structure. Although correlations between size measurements, for example between diameter and height, are strong (coefficients > 0.61 across all plots) and consistently positive, correlations between size and site variables (e.g., aspect) are weaker (coefficients < 0.41 across all plots) and inconsistent. Most plots demonstrated a weak but consistent relationship between size and age, and yew tree size and age distributions were relatively consistent within subregions. However, there were substantial differences in diameter growth rates among subregions