Because trees grow individual rings each year, tree ring dating -- dendrochronology -- is often used to determine the age of trees by looking at the growth pattern and matching all trees on a site using key signature rings, such as the small rings representative of a drought. In this way, the rings corresponding to the drought years of 1985, 1988, 1991 and 1995 were identified.
These rings were then compared to the average of their species growth during non-drought years in the area where they grew. The drought year tree rings were also compared to rings immediately before and after the drought.
Among the four sites studied, the dry ridge sites were most impacted by droughts and had the largest decreases in radial growth. Black cherry, which appeared in all four locations, had below average growth on the ridge and in the barrens, but not in the valley or in the wettest riparian area.
"Species in the valley and the barrens exhibited relatively few significant growth reductions in drought years compared to the ridge site," says Abrams. "Overall, there was not always a clear relationship between species moisture preference and their tree-ring growth during drought."
According to leaf response, pignut hickory and red oak are considered drought-tolerant species in riparian sites, but they had a disproportionate number of drought growth reductions in that area. In the valley, black oak and red maple both suffered large and frequent growth declines during drought, but are considered moderately to highly drought tolerant.
"It appears that there is an inconsistent pattern between leaf-level
physiology and radial growth," says Abrams. "More study is needed to see if and
how drought tolerant trees actually store energy in deep roots and why some
trees are putting energy into tr
Contact: A'ndrea Elyse Messer