An approach to modeling disturbance-based silviculture regimes in the forest vegetation simulator
The importance of accounting for edge creation from canopy openings when modeling long-term forest dynamics of natural disturbance-based silvicultural (NDBS) systems is not well understood. To address this issue, I used data from the Acadian Forest Ecosystem Research Program, a long-term, NDBS study in the Penobscot Experimental Forest in Bradley, ME, that uses expanding canopy gaps to approximate the natural disturbance patterns of northeastern United Stands and eastern Canada. My analytical approach combined use of univariate statistical analysis, resampling methods, and forest simulation models, namely the Forest Vegetation Simulator (FVS), to evaluate: 1) effects of canopy gaps on growth and regeneration dynamics of canopy-gap adjacent forest; 2) effects of alternative tactical implementations of NDBS systems on edge creation and longevity patterns; 3) impacts of increased growth rates in canopy-gap adjacent forest on long-term forest dynamic simulations of these complex alternative silvicultural regimes; and 4) potential production and financial returns of NDBS systems relative to conventional even- and uneven-aged systems. I observed differences in within-stand growth and regeneration patterns by position relative to harvest gaps edges. Overstory diameter growth rates in canopy gaps and along gap edges were generally greater than those observed in adjacent forests. Sapling growth and survival of mid-successional species were favored by large gaps (>1000 m2), while small gaps (<1000 >m2) favored late-successional species. In addition, edge dynamics differed markedly between the two expanding-gap systems. Relative to the large-gap treatment, the small-gap system design created a greater proportion of new edge with a different temporal distribution and greater longevity before being harvested from gap expansions. Accounting for these differences in edge creation patterns over time, in combination with increased growth rates in canopy-gap adjacent forest, caused minor increases in projected yields of merchantable products in long-term stand dynamics projections. These increases are likely severely understated due to limitations in the current FVS model structure. Despite these limitations, my preliminary production and financial analysis of NDBS systems suggests they will likely be a viable forest management tool capable of yielding competitive returns relative to conventional even- and uneven-aged treatments. Collectively, the findings of my investigation emphasized the importance of accounting for differences in overall quantity, longevity, and distribution of new edge creation over time when modeling forest dynamics following forest management with complex, alternative silvicultural regimes.
Saunders, Purdue University.
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