Historical and current stand structure in Douglas-fir and ponderosa pine forests.

Abstract

A comparison of historic and current stand structure and species composition was made in Douglas-fir (Pseudotsuga menziesii) and ponderosa pine (Pinus ponderosa) forest series on the eastern slopes of the Cascade Mountains. We used tree ring analysis of 1,192 tree cores from the Okanogan National Forest to reconstruct historical tree diameter and inferred structural attributes during the past 100 years. Sampled stands currently have more trees per acre and more basal area than were found historically. Overall stand density has increased 307% for Douglas-fir, 81% for ponderosa pine and 138% for Engelmann spruce (Picea engelmannii). Western larch (Larix occidentalis) was the only tree species that decreased in density (-48%). Average basal area has also increased 81% above historical levels. Changes in stand density have not been uniform over the past 100 years. The maximum number of trees per acre for most of these stands occurred 40 to 50 years ago, which indicates a shift toward a stem exclusion stage of stand development in recent decades.

Citation

Ohlson, Peter; Schellhaas, Richard. 2000. Historical and current stand structure in Douglas-fir and ponderosa pine forests. Unpublished Report