Economics of harvesting to maintain high structural diversity and resulting damage to residual trees

Abstract

We compared two harvesting prescriptions at the Blacks Mountain Experimental Forest in northeastern California: one that maintained high structural diversity by retaining larger, old-growth trees, and a more traditional approach that removed the overstory, thinned the vigorous younger trees, and removed the suppressed understory. We investigated two aspects: economics of harvesting and damage to residual trees. The low diversity treatment generated net revenue of $2600/ac due to the large volume of large sawlogs removed. The high diversity prescription resulted in a net loss of $300/ac due to the high harvesting costs and low product values associated with the smaller sawlogs, the low sawlog volume, and the negative net value of the small biomass trees. Leaving the smallest trees (4 in. dbh) on site would reduce the net loss by half but would also leave an additional three bone dry tons (BDT) of fuel/ac. The net revenue results are sensitive to the product values. If, for example, the delivered value of the biomass was $40/BDT instead of the assumed $20/BDT, the high diversity prescription would just break even. On average, 17 and 23% of the sampled leave trees were damaged in the high and low diversity treatments, respectively. Smaller trees were more likely to be damaged. Felling damage frequency also increased with the level of removals. Skidding damage was higher in plots with more leave trees and adjacent to skid trails. We developed logistic regressions to estimate the probabilities of damage. These can be applied to a leave tree stand table to estimate roughly how many trees will survive undamaged or to estimate how many trees must be initially selected as leave trees so that a desired number will remain undamaged after all harvesting activities. For the high and low diversity treatments respectively, approximately 120 and 180 initial leave trees/ac are needed to obtain 100 final leave trees/ac without major damage.