Sensitivity of carbon stores in boreal forest moss mats - effects of vegetation, topography and climate

Abstract

In northern regions, moss and lichen mats are the major carbon-cycling interface between soils and the atmosphere. We aimed to quantify sensitivity of ground layer nutrient stores to environmental predictors, to better understand interactions with vegetation, topography and climatic conditions. With non-destructive forest inventory techniques, we estimated distributions of biomass, carbon and nitrogen among moss/lichen ground layers in a 1.1 million-ha watershed within Alaska’s boreal forest region. Using nonparametric multiplicative regression, we fit response surfaces and quantified sensitivity to environmental predictors. Across 96 sites, half the ground layer biomass values were in the range 4750–18,900 kg ha−1 (25th to 75th percentiles). Carbon and nitrogen stores peaked in older stands and those with little forb cover (suggesting low disturbance) and low incident radiation. Among functional groups, the most abundant were nitrogen-fixing feather mosses, which formed extensive carpets. Nutrient stores were most sensitive to local vegetation and topography predictors, but less sensitive to regional climate. Moss and lichen mats in boreal forests are substantial carbon and nitrogen stores, with consequences for carbon sequestration and ecosystem productivity. Their environmental sensitivity suggests that ground layer nutrient stores could decrease if global changes promote vascular vegetation expansions and intensifying wildfire regimes.