Variability in oak forest herb layer communities
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In: Gottschalk, Kurt W.; Fosbroke, Sandra L. C., ed. Proceedings, 10th Central Hardwood Forest Conference; 1995 March 5-8; Morgantown, WV.: Gen. Tech. Rep. NE-197. Radnor, PA: U.S. Department of Agriculture, Forest Service, Northeastern Forest Experiment Station. 60-78
This study evaluates forest herb-layer sensitivity to annual-scale environmental fluctuation. Specific objectives were to determine the between-year variation in herb-layer community biomass, and to contrast and evaluate the temporal stability of spatial relationships in herb-layer community structure and composition between successive years. Aboveground dry weights of herbs and of woody species 4.5 cm dbh were estimated in June of 1988 and 1989 in 13 ecologically analogous, oak-dominated stands along a 170-km east-west transect in north-central Pennsylvania. An approximately 50% reduction in total herb-layer biomass was measured from 1988 to 1989, presumably due to a residual or lagged effect of the early summer drought in 1988. Herb biomass reductions were inferred to largely result from reduced plant size rather than decreased spatial distribution. Smaller and (or) less-consistent biomass reductions for woody species may have resulted from high first-year seedling mortality in the case of Acer rubrum L., and possibly from intensified deer browsing of shrubs and saplings as a consequence of reduced herb forage resulting from the drought. Classification and ordination also indicated a 1989 reduction in importance of mesic-type species and an increase in similarity of herb-layer communities among stands. Conversely, greater spatial differences in species diversity measures were evident in 1989. Comparisons among herb layer communities based on single or infrequent measurements may be misleading due to large temporal variability and the spatially differential responses that broad-scale environmental factors such as climate may superimpose. Monitoring herb layer biomass in this oak forest ecosystem offers a sensitive means for detecting short-term environmental fluctuations such as annual climate variation, and additional data may enable identification of vegetation trends with statistical confidence.
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McClenahen, J. R.; Long, R. P. 1995. Variability in oak forest herb layer communities. In: Gottschalk, Kurt W.; Fosbroke, Sandra L. C., ed. Proceedings, 10th Central Hardwood Forest Conference; 1995 March 5-8; Morgantown, WV.: Gen. Tech. Rep. NE-197. Radnor, PA: U.S. Department of Agriculture, Forest Service, Northeastern Forest Experiment Station. 60-78