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

Abstract

Aims A century of atmospheric deposition of sulfur and nitrogen has acidified soils and undermined the health and recruitment of foundational tree species in the northeastern US. However, effects of acidic deposition on the forest understory plant communities of this region are poorly documented. We investigated how forest understory plant species composition and richness varied across gradients of acidic deposition and soil acidity in the Adirondack Mountains of New York State. Methods We surveyed understory vegetation and soils in hardwood forests on 20 small watersheds and built models of community composition and richness as functions of soil chemistry, nitrogen and sulfur deposition, and other environmental variables. Results Community composition varied significantly with gradients of acidic deposition, soil acidity, and base cation availability (63% variance explained). Several species increased with soil acidity while others decreased. Understory plant richness decreased significantly with increasing soil acidity (r = 0.60). The best multivariate regression model to predict richness (p < 0.001, adjusted-R 2 = 0.60) reflected positive effects of pH and carbonto-nitrogen ratio (C:N). Conclusions The relationship we found between understory plant communities and a soil-chemical gradient, suggests that soil acidification can reduce diversity and alter the composition of these communities in northern hardwood forests exposed to acidic deposition.

Short-term effects of thinning on the development and communities of understory vegetation of Chinese fir plantations in Southeastern China

“…Previous studies had illustrated the soil nutrient contents were important factors which influenced the community compositions of the understory vegetation (Ploughe & Dukes, 2019;Zarfos et al, 2019). For example, Zarfos et al (2019) demonstrated that the community compositions displayed significant changes with different gradients of soil acidity, base cation availability, and carbon-to-nitrogen ratios (C:N). Furthermore, Legare et al (2001) found that the canopy types affected the understory compositions through impacting nutrient availability.…”

Acidic Deposition and Climate Warming as Drivers of Tree Growth in High-Elevation Spruce-Fir Forests of the Northeastern US

“…We stress that while the growth of high elevation red spruce has greatly increased, red spruce dominance in eastern forests is still well below historical levels (Hamburg and Cogbill, 1988;Wason et al, 2017b) and other tree species sensitive to atmospheric deposition-related soil acidification (e.g., sugar maple) are still experiencing declines (Bishop et al, 2015). While reduced atmospheric deposition has directly benefited red spruce growth, acid deposition will have a lasting legacy in northeastern U.S. forest ecosystems as acidified soils and plant communities are slow to recover (Driscoll et al, 2001;Battles et al, 2014;Lawrence et al, 2015;Zarfos et al, 2019); importantly, acidic deposition still remains a significant form of pollution in many forested areas globally (Vet et al, 2014).…”

Threshold effects of air pollution and climate change on understory plant communities at forested sites in the eastern United States

“…Such changes in soil and habitat conditions are expected to continue in the future with further changing air temperature and precipitation that may interact with effects of N deposition. At some locations, recovery from earlier soil acidification, predominantly caused by S deposition, continues to play a major role as a driver of vegetation response (Zarfos et al 2019).…”

“…Emissions of N have altered competitive interactions among plant species to favor nitrophilous species (Bobbink et al 2010, Clark et al 2019. Herbaceous plant species that are well-adapted to nutrient-poor conditions can be out-competed by other species that are better adapted to high N supply (Hautier et al 2009, Payne et al 2013, with potential effects on forest plant diversity (Gilliam 2007, van Dobben and de Vries 2017, Zarfos et al 2019. The former are often native and relatively rare; the latter are often non-native and invasive (Gilliam 2007).…”

“…Key processes include release of opportunistic species from N-limitation (Bobbink and Hicks 2014), competitive exclusion (Hautier et al 2009), soil acidification (Stevens et al 2010a), environmental filtering (Kraft et al 2015), base cation depletion (Zarfos et al 2019), and nutrient imbalances (Chen et al 2013).…”