Decadal Changes in Disjunct Eastern Hemlock Stands at Its Southern Range Boundary

Published:

Sept 2015

Author

Jared A. Myers

Additional Authors

Justin L. Hart Lauren E. Cox

Species distribution modelling has revealed shifts in the spatial distribution of the range of eastern hemlock (Tsuga canadensis (L.) Carri`ere) in eastern North America. Models project a decline in eastern hemlock at the southern portion of its range, but not contraction of the southern boundary. In 2003, the vertical, horizontal, and diameter structure and diameter-age relationships of eastern hemlock were quantified in 10 stands thought to represent the species’ 10 southernmost stands on the Cumberland Plateau in Alabama. In 2013, we resurveyed these stands to document changes in stand characteristics over the past decade. In addition, we explored additional reaches of stream corridors known to support eastern hemlock to document additional stands previously undescribed in the literature. Results from our resampling revealed that stands had similar stem frequencies over the 10-yr period, but, generally, the number of canopy stems and the number of seedlings declined. The decline in seedlings may have been a result of mortality or recruitment to larger size classes. The decline in canopy trees may have been caused by regional drought in 2007 or localized severe weather events. Our additional sampling yielded one stand not previously described. Although we cannot rule out additional disjunct stands in the area, we speculate that no eastern hemlock stands occur farther south than those documented here. Based on our results, we suggest that these stands are reproductively viable with episodic regeneration, and there has been no evidence of range contraction at the southern range limit over the past decade.

Keywords

Alabama, disjunct, eastern hemlock (Tsuga canadensis), range migration, regeneration