Macronutrient Depletion and Redistribution in Soils under Conifer and Northern Hardwood Forests

Abstract

While potentially important in the context of global biogeochemical change, the influence of different forest communities on chemical weathering rates in soils is poorly understood. We investigated the influence of four forest types (northern hardwood vs. three conifer plantations) on base cation depletion and redistribution in soils at Marsh–Billings–Rockefeller National Historical Park (MBRNHP) on 100‐yr forest development time scales. This site was ideal for the examination of forest‐type influence on the chemical denudation of the landscape during soil development due to a unique forest management history. Soils at MBRNHP are mildly acidic and developed on a silicate‐rich parent material with trace carbonates. Soil composition beneath different forest types indicates significant depth‐dependent differences in cation depletion. Conifer forest surface soils were more acidic and depleted in mineral‐phase base cations than those under northern hardwood forests. This was presumably due to aggressive weathering agents produced by fine‐root exudation and organic matter decomposition in conifer forest surface soils. At depth, there was a more acidic and sometimes cation‐depleted soil profile under northern hardwood relative to conifer forests, which could be associated with deeper root networks of northern hardwood species and related high nutrient demands, proton release, and mechanical weathering of deep soil. Depth‐dependent trends were more evident with Ca and Mg depletion profiles than Na and K, suggesting that vegetative enhancement of the weathering environment was most effective in dissolving more pedogenically reactive divalent cation mineral phases. This model of forest‐type enhancement of chemical weathering has important ramifications in the context of global biogeochemical change and forest management.