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

Michael R Zarfos,Timothy J Sullivan,Martin Dovciak,Todd C Mcdonnell,Gregory B Lawrence

doi:10.1007/s11104-019-04031-y

Abstract

AimsA 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.MethodsWe 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.ResultsCommunity 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-R2 = 0.60) reflected positive effects of pH and carbon-to-nitrogen ratio (C:N).ConclusionsThe 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.

Highlights

Biodiversity supports beneficial ecosystem functions such as productivity, resilience, and stability, while supporting a range of related ecosystem services (Dovciak and Halpern 2010; Cardinale et al 2012)
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
The ordination described a gradient in species richness that corresponded with the gradient in acidic deposition, soil acidity, and nutrient availability represented by axis 1 (Fig. 2)

Summary

Introduction

Biodiversity supports beneficial ecosystem functions such as productivity, resilience, and stability, while supporting a range of related ecosystem services (Dovciak and Halpern 2010; Cardinale et al 2012). Acidic deposition in the northeastern US has declined over time as a result of air pollution control legislation (Driscoll et al 2001; Wason et al 2017) regional soils have shown only limited recovery as their base cations remain depleted and Al remains mobile (Lawrence et al 2015a). The effects of historical acidic deposition were greatest in regions with areas of basepoor bedrock and till such as the Adirondack Mountains (Driscoll et al 2001) where forest soil acidification and losses of Ca and other base cations have been well documented (Johnson et al 2008; Warby et al 2009). Understory plants represent the majority of plant species in temperate forests and contribute disproportionately (relative to their biomass) to net primary productivity, Plant Soil (2019) 438:461–477 ecosystem nutrient cycling, food web structure, species interactions, and biodiversity (Gilliam 2007, 2014)

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Results

Discussion

Conclusion