Bark-stripping patterns in bristlecone pine (Pinus aristata) stands in Colorado, USA1

Abstract

Bark-stripping, or partial cambial mortality, is characteristic of Rocky Mountain bristlecone pine (Pinus aristata). The cause of this phenomenon is unknown, but previous work has shown a correlation between stripping and wind directions. We examined bark-stripping patterns in ten Pinus aristata stands in Colorado. For every strip, we recorded its relative position on the trunk and the direction of the strip top and bottom. Strips were assigned to one of 10 class-position types based on their relative lengths and positions. Mean top and bottom strip directions ranged from ∼225° to due north (0°). Site aspect ranged from 98° to 249°, whereas estimated wind direction ranged from 261° to 30°. Almost all of the small strips were on the lower half of the trunk. The directions of small strips near trunk bases were widely dispersed, whereas small strips higher on the trunk were more narrowly dispersed and oriented close to wind direction. Patterns of stripping and of abrasion of pencils fastened to trunks suggest that most strips that develop into larger ones are initiated by wind abrasion and extend primarily upward. Our findings are consistent with the model of Matthes et al. (2002) for the formation and possible function of bark-stripping.