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Journal of Undergraduate Research

Keywords

Quaking aspen, Populus tremuloides, drought, clone

College

Life Sciences

Department

Plant and Wildlife Sciences

Abstract

Quaking aspen, Populus tremuloides, is a keystone species in forest ecosystems and is the most widely distributed tree in North America (St. Clair, Guyon, and Donaldson, 2010). Although it covers less than 10% of the forested landscape, aspen contributes disproportionately to water yield and plant and animal diversity (Kaye, Binkley, and Stohlgren, 2005). Severe drought and increased temperature in recent decades have contributed to largescale aspen die‐offs, (Worrall et al. 2007, Anderegg et al. 2012) likely through a process called hydraulic failure. Hydraulic failure occurs under drought conditions when the pressure required to draw water up a tree’s vascular tissue produces air bubbles (cavitation) that block water and nutrient flow and slowly kill the tree from the top down (Sperry et al. 1994). Field observations (Worral et al 2007) suggest that hydraulic failure primarily affects older aspen trees, implying that younger trees might better survive drought and thus perpetuate the clonal stand. Increasing evidence shows that young trees in many aspen stands have been reduced or eliminated through excessive browsing by livestock and wildlife (Kaye, Binkley, and Stohlgren, 2005). If data show that young trees enhance an aspen clone’s ability to cope with drought, then management measures should be taken to protect young trees from heavy browsing pressure. Previous studies have examined age influence on aspen leaf traits (Smith et al. 2011), compared cavitation among different species of trees (Sperry et al. 1994), and assessed the role of hydraulic failure in drought-stressed mortality in aspen (Anderegg et al. 2012). Unpublished data from the St. Clair lab show that cavitation is more prevalent among aspens at lower elevations than at higher elevations. However, none of these studies compared cavitation among different age classes in an aspen clone, which will help us better understand the clone’s ability to cope with hydraulic stress and the consequences of losing younger aspen stems to heavy browsing pressure.

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