Recent mortality and decline in mature Abies amabilis: the interaction between site factors and tephra deposition from Mount St. Helens
Segura, G. | Brubaker, L.B. | Franklin, J.F. | Hinckley, T.M. | Maguire, D.A. | Wright, G.
Patterns of decline of mature and old-growth stands of Abies amabilis (Dougl.) Forbes (Pacific silver fir) induced by tephra deposition from the 1980 eruption of Mount St. Helens were analyzed at the landscape level using discriminant and least squares regression analysis. From an array of environmental and biological factors, only the thickness of fine A3 tephra deposit, elevation, and the relative dominance of A. amabilis in a stand showed significant effects on decline. Stand decline, a mean value of the decline conditions of individual trees in a stands increased with increasing amounts of A3 tephra and decreased with increasing elevation and relative dominance of A. amabilis. Elevation and relative dominance of A. amabilis were positively correlated, complicating the interpretation of each variable alone; we suspect that each individually represents conditions that influenced the vigor A. amabilis predisposing it and (or) contributing to the initial tephra-induced stress and, therefore, affecting its survival and recovery.
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