Influence of Bedrock and Aspect on Soils and Plant Distribution in the Holyoke Range, Massachusetts

• Published in: The journal of the Torrey Botanical Society Vol. 130; no. 3; pp. 158 - 169
• Main Authors: Searcy, Karen B., Wilson, Brayton F., Fownes, James H.
• Format: Journal Article
• Language: English
• Published: Lawrence Torrey Botanical Society 01.07.2003
• Subjects: Arkoses; Basalt; Basaltic soils; Bedrock; Forest soils; Plants; Shrubs; Taxa; Topographical aspect; Vegetation; USA, Massachusetts
• ISSN: 1095-5674; 1940-0616
• DOI: 10.2307/3557551

We explored the extent to which bedrock and aspect influenced soil and vegetation patterns in the Holyoke Range, an east-west oriented basalt ridge in the Connecticut River Valley of Massachusetts. Pairs of plots were sampled at 53 locations along the contact zone between arkose and basalt, 29 pairs on the south and 24 pairs on the north side of the range. For each plot we measured slope, plot aspect, soil pH and soil nutrients, the importance value for trees, within-plot frequency for shrubs and recorded presence/absence for herbaceous taxa. Soil on basalt had a higher pH and was richer in nutrients, particularly exchangeable Ca and Mg than soil on arkose. Principal Components Analysis of plots using soil variables indicated that those associated with bedrock accounted for 51% of the variance while soil differences related to aspect accounted for 22%. The multi-response permutation procedure indicated significant differences in distribution in all vegetation layers with respect to both bedrock and aspect. Species richness on basalt was significantly higher for both trees and herbaceous plants, and was also higher on the south side of the range for herbaceous plants. Of the 89 species present in more than 5% of the plots, 32% had significantly different distributions with respect to bedrock alone, 21% differed significantly with respect to both bedrock type and aspect while only 9% differed significantly with aspect independent of bedrock. The largest differences were in the herbaceous layer. Canonical correspondence analysis using soil and site variables indicated that for all vegetation layers the strongest gradient was related to bedrock.