The effect of soil nutrition, soil acidity and drought on northern red oak ( Quercus rubra L.) growth and nutrition on Pennsylvania sites with high and low red oak mortality

Unexplained mortality of northern red oak ( Quercus rubra L.) has occurred on the Laurel Hill in southwestern Pennsylvania. We attempted to characterize this mortality and determine its relationship to soil acidity, soil nutrient status and droughts. Three blocks with high and low mortality of northern red oak were selected. Basal area increment, terminal elongation and leaf mass were measured along with soil chemistry. Basal area growth patterns were compared to historic drought records. Both living and standing dead trees on high mortality plots had been responsive to most of these droughts. After 2 years of droughts in the 1960s, basal area growth rate of trees on high mortality plots did not recover. In addition, the standing dead trees on high mortality plots were historically a less vigorous subset. After this mortality, the living trees did not respond with increased growth due to thinning of competitors. Basal area growth on low mortality plots did recover after these same droughts and mortality was limited. In addition, the trees on the high mortality plots showed foliar deficiency of K and low levels of Ca while trees on the low mortality plots did not. Furthermore, the A- and B- horizons of the soils on the high mortality plots had lower levels of soil bases, higher levels of available Al and lower Ca/Al ratios. The results of this study suggest that nutrient deficiency and associated Al toxicity may be causing stress for northern red oaks and is related to the mortality and reduced growth of northern red oak in this region.