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Williams, Laurel P.

Natural Resources

2006

MS

Late-successional/old-growth (LSOG) forest is underrepresented on the landscape as compared to pre-European settlement levels. Agencies and researchers are exploring ecologically-based silvicultural techniques for restoration of LSOG structural characteristics, which include large trees and structural complexity. One such technique, termed "structural complexity enhancement" (SCE) is being tested at a northern hardwood forest site in Vermont, USA. We used the individual-tree based, spatially explicit SORTIE-ND, parameterized with site-specific data and Neighborhood Competition Indices (NCI), to model future treatment effects. We linked model output from projection years 50 and 100 to the Structural Complexity Index (SCI). Treatment effects persisted for ~150 years. Projected stand development rates were higher in STS units than in SCE units regardless of treatment. We traced the cause to an interaction of beech bark disease with unit-specific species dynamics. Persistent slow-growing beech thickets developed and shaded out other regeneration while failing to develop themselves. Within this context, SCE treatment showed promising retention and development of large trees, as well as better retention of structural complexity, as compared to a single tree selection treatment. In SCE treatment scenarios, large tree basal areas closely tracked those of no-treatment scenarios for the first 50 years. Neither treatment appeared significantly superior to no-treatment scenarios in developing large trees or improving complexity by year 100. Red spruce, historically >30% of the stand and preferentially retained, became dominant after ~year 300, and was enhanced by treatment. Analysis of additional existing SCE units at another existing location is recommended to elucidate SCE effects. This is the first published use of SORTIE-ND with NCI values for New England, of structural analysis of SORTIE output, and of SORTIE linked to SCI.