Moisture availability is a key factor influencing white oak (Quercus alba L.) growth and productivity. In unglaciated areas of eastern North America, available moisture varies greatly along topographic and edaphic gradients. Climatic conditions have also been shown to influence moisture availability. The integrated moisture index (IMI) is a GIS-derived soil moisture index that combines topographic and soil features (hillshade, flow accumulation, curvature, and water holding capacity) into a single index for comparing various ecological processes including forest growth and productivity. The goal of this study was to determine how moisture gradients affect white oak radial growth in four mixed-oak forests in southern Ohio. To this end, 238 increment cores were extracted from 119 white oak trees growing across IMI gradients (xeric, intermediate and mesic) in four mixed oak forests. The increment cores were cross-dated, measured and standardized according to standard dendrochronological procedures. Standardized ring widths were used to composite chronologies for each of the three IMI categories. Basal area increment (BAI) was computed as an indicator of growth for each ring width. To assess the climate-radial growth relations, correlation analyses were performed using indexed ring width, mean monthly precipitation, temperature and Palmer Drought Severity Index (PDSI).
Growth rate varied considerably across the IMI classes with trees in the xeric sites exhibiting patterns much different from those in either xeric or intermediate sites. Basal area increments were consistently higher in both mesic and intermediate sites than in xeric sites. The signal/noise ratio and correlation among all cores and trees were highest for the xeric composite chronology. Composite IMI chronologies correlated significantly with macroclimatic variables (PDSI, precipitation and temperature, N = 101, p < 0.05). Both current (t) and previous (t - 1) year growing season climatic variables were significantly correlated with annual growth. Climate influences on growth rate were also variable across the IMI gradient with trees in xeric and mesic sites showing the greatest and least responses respectively. These results suggest a strong mechanistic link between white oak growth and moisture availability. The climate signal observed in this study is comparable to growth/climate patterns observed in other regional studies, and suggests that climate is an important driver of white oak growth. The results also indicate the usefulness of the IMI for identifying and comparing white oak growth patterns across the complex landscape of southern Ohio.