Shifting Rainfall Patterns May Change Southern Appalachian Forest Structure

A new research study by U.S. Forest Service scientists finds that changes in rainfall patterns in the southern Appalachians due to climate change could reduce growth in six hardwood tree species common to the region. The findings have implications for forest managers in the Southeast, where climate variability (more extreme events or changes in precipitation distribution) could cause major shifts in forest composition and structure.

The study, recently published online in the journal Global Change Biology, evaluated climate-driven patterns of growth for six dominant hardwood tree species in the southern Appalachians in relation to their topographic positions on slopes or in coves.

One group of trees – maple, poplar, and birch – are diffuse-porous, meaning they form many vessels of similar size throughout the xylem (the water conducting tissue of the tree), and tightly regulate water loss during the day by closing their stomata, the tiny holes in leaves that release water into the air. The three species of oaks in the second group form large vessels in a distinct ring in the xylem (ring-porous), and control water loss through stomata less tightly.

The researchers sampled 465 trees to evaluate tree ring growth in relation to 70 years of on-site climatic data. They found that diffuse-porous species (maple, poplar, birch) growing on dry sites were the most sensitive to climate, while the ring-porous species (oak) were the least sensitive.

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