Conversion of even-aged slash pine to uneven-aged stands: Evaluation of harvest regimes and uneven-aged management using simulation modeling

Background/Question/Methods

There is an ever-increasing interest in managing forest stands as uneven-aged structures for a variety of commodity and non-commodity benefits including timber production, carbon sequestration, biodiversity enhancement, and other environmental services, in a sustainable manner. Consequently, land managers in the southeastern United States are under increased pressure to convert slash pine (Pinus elliottii Engelm.) plantations, among other southern pines, into uneven-aged structures and apply selection silviculture in their management. Lacking experience with uneven-aged silviculture,however, land managers are applying partial cuttings to the even-aged stands across increasing acreage, based on their best guess, in an effort to convert them to uneven-aged structures, with uncertainty of its implications for stand structural complexity, carbon sequestration, and timber production. In this study, we collected overstory data from a mature slash pine plantation at Tate’s Hell State Forest, FL, and used Forest Vegetation Simulator (FVS) model to evaluate a total of 49 conversion scenarios that encompassed a range of combinations of harvest intensity (residual basal area), frequency (cutting cycle), and regeneration for their effectiveness to create structural diversity, sequester carbon, and produce merchantable timber over a period of 100 years.

Results/Conclusions

The scenarios which resulted in higher structural diversity generally led to lower carbon sequestration as well as merchantable timber production, and vice versa. The scenarios that followed BDq cut beginning first cut resulted in higher structural diversity, whereas low thinning during first cut led to higher merchantable timber production. Longer cutting cycle resulted in decrease in structural diversity in all scenarios. Except for the scenarios of high basal area with BDq cut from beginning, however, carbon sequestration and merchantable timber production increased with increase in length of cutting cycle. Best scenarios which maximized structural diversity, carbon sequestration, or merchantable timber production were identified, as well as the scenarios that optimized the provision of all these benefits collectively. When maintained at a low residual basal area of 4.6 m² ha^-1, low thinning at first cut with 20 year cutting cycle and regeneration of 741 or more seedlings/hectare optimized the provision of multiple benefits. At higher residual basal area of 11.5 m² ha^-1, low thinning at first cut with 10 year cutting cycle and regeneration of 247 seedlings per acre optimized provision of structural diversity, carbon sequestration, and merchantable timber. Depending on the overriding objectives of the land owning agency, the study has recommended appropriate set of harvest regimes and management.