Effects of visitation on substrate depth and community structure within the granite outcrops of Welch Mountain, New Hampshire

Hilke, Christopher J.
Tom Wessels, MA
Department of Environmental Studies
The exposed granite ledges on Welch Mountain, New Hampshire provide a popular scenic destination point for numerous dayhikers every year. Physical evidence suggests that the granite outcrop communities that occur along these ledges having been receding due to erosion. The purpose of this research was to investigate if specific structural and compositional characteristics were significantly affected by the proximity of a vegetation “island” community to the primary access trail. The study investigates three primary questions: is there a relationship between the suite of species in an island community and the distance of that island from a primary trail? Secondly, is there a relationship between the distance of the island from the trail and substrate depth? Lastly, is there a relationship between the distance of an island community from the trail and its percent vegetation cover? During the summer and fall of 2006, 149 plots were randomly selected along the ledges on Welch Mtn. Species composition, substrate depth, substrate type, exposure orientation, elevation, and slope were determined at each sampling point. The data indicated that there was a correlation between specific species occurrence and specific soil depths. Further analysis demonstrated that the distance of the plot from the trail significantly effected mean soil depth. Analysis of Variance indicated that there was a significant difference in the variability of means between species occurrence and the distance of the plot from the trail, yet failed to find a significant association between the percent cover of a specific species and the distance of that plant from the trail. As a whole, the data suggests that the distribution of species is dependent first and foremost on substrate availability and environmental stress. The high degree of baseline abiotic stress inherent to Welch mtn. granite outcrop environments suggests that these communities may be particularly susceptible to visitor trampling.

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