Moose directly slow plant regeneration but have limited indirect effects on soil stoichiometry and litter decomposition rates in disturbed maritime boreal forests

Abstract

Summary Foraging decisions by herbivores are modulated by physiological demands for nutrients and these decisions can influence the biomass, abundance and dynamics of plant species with consequences on key ecosystem processes, such as nutrient cycling and decomposition. Some studies have found that large browser populations can reduce the abundance of nutrient‐rich preferred species, promoting the dominance of nutrient‐poor non‐preferred species. This can have indirect effects on soil nutrient concentrations, soil microbe community composition and above‐ground invertebrates and birds that depend on nutrient‐rich plant species. However, very little research has compared the impact of biotic and abiotic features on nutrient cycling and decomposition in areas of high moose density. We performed a field study to test the generality of moose effects on forest ecosystems observed in iconic study systems such as Isle Royale. Specifically, we used 10 paired moose exclosure and control plots to test the effects of moose on plant community characteristics, litter fall quantity, soil properties and litter decomposition rates in regenerating disturbed forests in Newfoundland, Canada. We found evidence that moose reduce plant height and plant litter biomass, thereby affecting the quantity of carbon, nitrogen and phosphorus available in litter fall with potential indirect effects on soil pH and soil depth. However, we found no evidence that the direct effects of moose lead to indirect effects on soil quality, soil moisture and litter decomposition rates. Disturbance regime and site explained a large portion of the variance in plant community characteristics, litter fall quantity, soil properties and litter decomposition. Our results suggest that while introduced moose in Newfoundland have measurable direct influence on plant regeneration and litter fall biomass, other factors such as disturbance history and climate may be more important predictors of landscape‐scale variation in soil quality and litter decomposition rates. Our study suggests a need for further development of theory to predict the relative contribution of biotic vs. abiotic effects on nutrient cycling in forest ecosystems. A lay summary is available for this article.