Sustained timber yield claims, considerations, and tradeoffs for selectively logged forests

Abstract

What is meant by sustainability depends on what is sustained and at what level. Sustainable forest management, for example, requires maintenance of a variety of values not the least of which is sustained timber yields (STYs). For the 1 Bha of the world's forests subjected to selective or partial logging, failure to maintain yields can be hidden by regulatory requirements and questionable auditing practices such as increasing the number of commercial species with each harvest, reducing the minimum size at which trees can be harvested and accepting logs of lower quality. For assertions of STY to be credible, clarity is needed about all these issues, as well as about the associated ecological and economic tradeoffs. Lack of clarity about sustainability heightens risks of unsubstantiated claims and unseen losses. STY is possible but often requires cutting cycles that are longer and logging intensities that are lower than prescribed by law, as well as effective use of low-impact logging practices and application of silvicultural treatments to promote timber stock recovery. These departures from business-as-usual practices will lower profit margins but generally benefit biodiversity and ecosystem services.

Keywords: climate change mitigation; forest management; natural climate solutions; nature based solutions; timber growth and yield.

Fig. 1.

Standing volumes of timber from natural forests subjected to selective harvests of trees greater than some MCD at 30-y intervals. On the Y-axis, which shows standing timber volumes, 30 m³ha^–1 is used as the maximum only for illustrative purposes.

Fig. 2.

Theoretical but seldom realized STY; the numbers refer to variables explored in the text and illustrated in subsequent figures. #1 pertains to the many different variables that can be plotted on the Y-axis. #2 represents the volume at which yields are to be sustained. #3 represents variations in cutting cycle duration. #4 concerns harvest intensity. #5 shows temporary increases in tree mortality after a selective harvest, as influenced by logging intensity and use of reduced-impact logging practices. #6 refers to the speed of timber volume recovery, as influenced by logging practices and silvicultural treatments.

Fig. 3.

Timber yields sustained by lengthening cutting cycles (solid line), reducing harvest intensity (dotted line), or accepting a primary forest premium of 50% (dashed line).

Fig. 4.

Timber recovery after RIL (solid line) or RIL followed by application of silvicultural treatments that enhance stand recovery rates (dashed line).