CLUSTERING TIMBER HARVESTS AND THE EFFECT OF DYNAMIC FOREST MANAGEMENT POLICY ON FOREST FRAGMENTATION

To integrate multiple uses (mature forest and commodity production) be tter on forested lands, timber management strategies that cluster harv ests have been proposed. One such approach clusters harvest activity i n space and time, and rotates timber production zones across the lands cape with a long temporal period (dynamic zoning). Dynamic zoning has been shown to increase timber production and reduce forest fragmentati on by segregating uses in time without reducing the spatial extent of timber production. It is reasonable to wonder what the effect of perio dic interruptions in the implementation of such as strategy might be, as would be expected in a dynamic political environment. To answer the se questions, I used a timber harvest simulation model (HARVEST) to si mulate a dynamic zoning harvest strategy that was periodically interru pted by changes in the spatial dispersion of harvests, by changes in t imber production levels, or both. The temporal scale (period) of these interruptions had impacts related to the rate at which the forest ach ieved canopy closure after harvest. Spatial dynamics in harvest polici es had a greater effect on the amount of forest interior and edge than did dynamics in harvest intensity. The periodically clustered scenari os always produced greater amounts of forest interior and less forest edge than did their never clustered counterparts. The results suggest that clustering of harvests produces less forest fragmentation than di spersed cutting alternatives, even in the face of a dynamic policy fut ure. Although periodic episodes of dispersed cutting increased fragmen tation, average and maximum fragmentation measures were Less than if c lustered harvest strategies were never implemented. Clustering may als o be useful to mitigate the fragmentation effects of socially mandated increases in timber harvest levels. Implementation of spatial cluster ing during periods of high timber harvest rates reduced the variation in forest interior and edge through time, providing a more stable supp ly of forest interior habitat across the landscape.