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South or west: why do aspect preferences of xerophytic pine stands vary along the southern Appalachian Mountains?

Authors: Charles Lafon*, Texas A & M University, Alison Hanson, Halff Associates, Rosemary Olson, Independent contractor, Sam Norris, Texas A&M University, Bruce Eaves, Texas A&M University
Topics: Biogeography
Keywords: landscape pattern, Pinus pungens, Pinus rigida, tree distribution, vegetation patch
Session Type: Poster
Presentation File: No File Uploaded

This study addresses vegetation patchiness associated with slope aspect in mountainous terrain, where equatorward-facing slopes have xerophytic vegetation favored by high insolation and low moisture. Specifically, we investigate the patterning of montane pine stands in the southern Appalachian Mountains. These stands consistently occupy south- and southwest-facing slopes in the southern half of the study area, meaning they are associated with the most strongly illuminated slope aspects. This is the typical pattern for xerophytic vegetation across the northern hemisphere. However, in the northern half of the study area, pines are more widely distributed, with greatest extent on west-, southwest-, and even northwest-facing slopes. This misalignment of xerophytic vegetation with insolation suggests the influence of other factors. We explore other abiotic factors (topographic wetness and wind) but find they provide only partial explanation for the misalignment. Additionally, in light of the pyrogenic nature of the pine stands, we investigate the possible influence of fire severity on their topographic distribution. We present a conceptual model of the long-term coevolution of pine forest with microclimates, fire regimes, soils, and landforms.

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