Soil Base Saturation Combines with Beech Bark Disease to Influence Composition and Structure of Sugar Maple-Beech Forests in an Acid Rain-Impacted Region

Plant richness and composition in hardwood forest understories vary along an acidic deposition and soil-chemical gradient in the northeastern United States

“…As a result of these two factors, the impact of acidic deposition on soil acidity is likely to decrease from west to east in the park (Sullivan et al 2013b). We surveyed 20 watersheds distributed throughout the Adirondack Park that had been studied previously to capture these gradients in acidic atmospheric deposition and associated soil acidification (Sullivan et al 2013b;Bishop et al 2015;Lawrence et al 2017a). We hypothesized that, along this spatial gradient, (H1) high soil acidity and low base saturation would be associated with low understory plant species richness and community composition reflecting species tolerant of acidic soils, and (H2) acidic deposition and soil acidbase status would have stronger relationships to understory plant composition and richness at regional scales than environmental factors such as light and moisture.…”

A Newly Identified Role of the Deciduous Forest Floor in the Timing of Green‐Up

“…Soil pH, as we measured it, was largely a function of soil water chemistry and hydrogen ion weakly adsorbed to soil surfaces, whereas exchangeable H + was determined by an extractant that was nearly 100 times more concentrated than the extractant used in measuring pH. The mobility of aluminum in soil increases with increasing acidity, but concentration of inorganic monomeric aluminum, the form mobilized by acidic deposition, is not a function of acidity when soil base saturation is greater than 17 (the aluminum mobilization threshold), which was the condition for approximately one third of the study watersheds (Lawrence, McDonnell et al, ). Furthermore, aluminum mobility is also controlled by complexation with soluble organic matter, which generally renders the aluminum nonharmful to plants, but can also influence concentrations of exchangeable Al 3 + (Dijkstra & Fitzhugh, ).…”

“…Stream chemistry collected at the watershed pour point represents an integration of biogeochemical processes (including edaphic processes) within the study watersheds. Therefore, one of the variables we used in this study characterizes the overall state of watershed acidification (ACID) and was derived via a comparison of soil and stream water chemistry (Lawrence, McDonnell et al, ). The soil plots were selected to fall within these selected watersheds to include a hardwood forest that was relatively consistent in composition across plots.…”

“…In addition to these conventional characteristics of soil acidity, we also included a variable (termed ACID) that reflected whether or not acidic deposition was causing mobilization of soil aluminum. This characteristic was derived through a comparison of soil and stream samples collected from the same watersheds (Lawrence, McDonnell et al, ). ACID is a categorical variable with three possible values: acidified (ACID(A)), buffered (ACID(B)), and neutral (ACID(N)).…”

“…In acidified watersheds, mobilization of aluminum within the soil is reflected by measureable inorganic monomeric Al in surface waters (Lawrence et al, ), whereas in watersheds with sufficient acid buffering capacity, this form of Al is not mobilized. The mobilization of Al within soils from acidic deposition is a threshold process that occurs when base saturation decreases below about 17% (Lawrence, McDonnell et al, ). Bulk Density (BD) was calculated from LOI by the method of Federer et al, () for northeastern forest soils.…”