Abstract

Alnus crispa (green alder) is a nitrogen-fixing, circumboreal shrub distributed throughout Canada and the northeastern United States with disjunct populations in the central and southern Appalachians. In North Carolina and Tennessee, it is classified as a species of special concern that occurs within the globally rare green alder bald community type at high elevations in Roan Highlands. Over recent decades, the alder balds and adjacent grassy balds have been invaded by blackberry (Rubus spp.). Blackberry growing near alders could compete for sunlight, nitrogen, and other soil nutrients, which could impact the vigor of the alders and possibly benefit the blackberry. My objective was to better understand how these interactions affected the leaf chlorophyll of blackberry and green alder. Over the summer, we measured leaf chlorophyll of blackberry and alder in low and high blackberry cover plots as well as plots without alder. We measured the height of alder stems and blackberry canes and counted green alder vegetative root sprouts. Linear regression showed that blackberry leaf chlorophyll and height were not significantly different in plots with and without alder. However, alder leaf chlorophyll and height were significantly greater in plots with high blackberry cover compared to plots with low blackberry cover. This could indicate that alders and blackberries favor certain microsites. In addition, alder in plots with high blackberry cover produced fewer root sprouts (presumably due to excessive shading), which may have long-term consequences for the persistence of green alder at Roan Highlands. Management efforts currently focus on cutting blackberries close to the Appalachian Trail that passes through Roan Highlands, leaving green alder growing away from the trail surrounded by dense thickets of blackberry. We recommend that blackberry management be extended to alder patches downslope and away from the trail, which will involve careful hand clipping to not damage alder stems.

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