Forest dynamics along the elevation gradient in the Great Smoky Mountains

Background/Question/Methods

How old, unmanaged forests change over time is poorly understood. Information on the rates and mechanisms of change within stands and along landscape gradients is incomplete. The forest vegetation and environmental gradients of the Great Smoky Mountains are well studied. Long-term data on forest dynamics build on the findings of earlier short-term studies. Rates of tree species ingrowth, growth and mortality within and among intensive long-term study stands along the elevation gradient serve to clarify mechanisms underlying the dynamics of forest vegetation and ecosystems. More than 30 long-term study stands were resampled to assess temporal changes in vegetation and ecosystem properties of unlogged forests in the northeastern Great Smoky Mountains. Stand elevations ranged from 700 to 2000 m. Thirteen of the stands were sampled intensively using a large plot (0.4-1.0 ha) with mapped trees. The remaining stands were sampled using variable-radius plot clusters.

Results/Conclusions

Over the last 50-80 years, the most striking changes have involved pests and pathogens. Such changes include the decline and partial recovery of Fraser fir, the partial decline of beech, and the severe decline of eastern hemlock. In some stands, this has caused marked changes in tree species dominance, strong declines in live biomass, and transfer of carbon to detritus pools. Some gradual changes from ecological succession or other processes were also detected. Direct effects of climate change on forest tree species composition were not obvious, although further examination of the data is warranted before solid conclusions can be reached. No invasions of tree species atypical of a given elevation in historical time were noted.