Canopy tree - soil interactions within temperate forests: effects of soil elemental composition and texture on species distributions

We compared the distribution of adult trees and relatively stable soil properties as part of a study of feedbacks between canopy tree species and soils. In southern New England, soils under Fraxinus americana L. (FRAM) and Acer rubrum L. (ACRU) had high contents of total CaO and MgO. Under Quercus rubra L. (GURU) and Fagus grandifolia Ehrh. (FAGR), contents of CaO and MgO were low. Sites with Acer saccharum Marsh. (ACSA) and Tsuga canadensis (L.) Carr. (TSCA) varied across a wide range of total CaO and MgO. However, below 0.8% CaO, ACSA was absent and FAGR, GURU, and TSCA were dominant. From 0.8 to 1.5% CaO, ACSA and FRAM increased with increasing CaO content, while the frequency of other species declined. Above 1.5% CaO, there was no relationship between CaO content and ACSA and FRAM abundance, but FAGR and QURU were largely absent. Canopy tree species also varied significantly with texture, which we attribute to the higher Ca and Mg contents of the more sandy soils, rather than to soil physical effects. Correlations between Ca availability and forest composition are well known for calcareous versus noncalcareous soils. Apparently, much subtler variations in supply of mineral nutrients also alter competitive interactions and impose patterning on the distribution of canopy trees within stands.