Tree architecture as a predictor of growth and mortality after an episode of red oak decline in the Ozark Highlands of Missouri, U.S.A.

Abstract

Mixed oak stands in the Ozark Highlands of southern Missouri were revisited eight years after a severe episode of red oak decline to determine which predictor variables, collected in 2003, best predicted subsequent tree growth and mortality patterns. Between 2002 and 2009, the mortality rate was 5% (0.625% annual mortality rate), generally below previously reported background rates. Generalized linear mixed models indicated that dieback (an estimate of branch mortality), age, relative height, and the interaction between the last two were most effective at predicting tree mortality. By contrast, tree vigor index (TVI), a composite variable derived from basic measurements of crown and stem architecture, was unequivocally the best predictor of basal area growth trend from one long-term period to the next. Basal area growth increases linearly with TVI, reinforcing the notion that even in ring-porous oaks (which must build new earlywood vessels each year), sustained growth is a low priority for carbon allocation in chronically stressed trees. The findings validate TVI as a useful metric for predicting growth rates of scarlet oak (Quercus coccinea Münchh.) and black oak (Quercus velutina Lam.).