Longevity of windthrown logs in a subalpine forest of central Colorado

Abstract

The number of years since tree death for wind-thrown logs of lodgepole pine (Pinus contorta var. latifolia Engelm.) and Engelmann spruce (Picea engelmannii Parry) was used to examine the longevity of this component of coarse woody debris in an old-growth subalpine forest in the central Rocky Mountains. Death dates of downed logs were determined by dendrochronological cross-dating methods. We were able to determine death dates for 73 logs from both species, the oldest being a lodgepole pine dead 139 years ago. Sound lodgepole pine and Engelmann spruce logs lying on the ground persisted for many decades with a majority of their volume intact. No difference was seen in decay classes of logs collected from two primary study sites on opposite (north and south) exposures. There was also no significant difference in decay classes between the two species, although lodgepole pine logs were in general older than Engelmann spruce logs within any decay class. There was little decrease in the specific gravity of wood remaining in logs with time, although there was a corresponding greater loss of wood volume.