Winter climate change implications for decomposition in northeastern forests: comparisons of sugar maple litter with herbivore fecal inputs

Abstract

Forests in northeastern North America are influenced by varying climatic and biotic factors; however, there is concern that rapid changes in these factors may lead to important changes in ecosystem processes such as decomposition. Climate change (especially warming) is predicted to increase rates of decomposition in northern latitudes. Warming in winter may result in complex effects including decreased levels of snow cover and an increased incidence of soil freezing that will effect decomposition. Along with these changes in climate, moose densities have also been increasing in this region, likely affecting nutrient dynamics. We measured decomposition and N release from 15 N-labeled sugar maple leaf litter and moose feces over 20 months in reference and snow removal treatment (to induce soil freezing) plots in two separate experiments at the Hubbard Brook Experimental Forest in New Hampshire, USA. Snow removal/soil freezing decreased decomposition of maple litter, but stimulated N transfer to soil and microbial biomass. Feces decomposed more rapidly than maple litter, and feces N moved into the mineral soil more than N derived from litter, likely due to the lower C : N ratio of feces. Feces decomposition was not affected by the snow removal treatment. Total microbial biomass (measured as microbial N and C) was not significantly affected by the treatments in either the litter or feces plots. These results suggest that increases in soil freezing and/or large herbivore populations, increase the transfer rate of N from plant detritus or digested plants into the mineral soil. Such changes suggest that altering the spatial and temporal patterns of soil freezing and moose density have important implications for ecosystem N cycling.

White‐tailed deer (Odocoileus virginianus) positively affect the growth of mature northern red oak (Quercus rubra) trees

“…The first we refer to as the deer waste mechanism. Deer can contribute substantial nutrients to ecosystems through the deposition of fecal and urine deposits (Christenson et al 2010, Jensen et al 2011. When deer consume food rich in N, they excrete excess N in their urine as urea, a form of N readily available to plants (Mengel andKirkby 2001, Pastor et al 2006).…”

Snow depth, soil freezing and nitrogen cycling in a northern hardwood forest landscape

“…In the northeastern US, watershed NO 3 -export increased at several sites following extensive soil freezing in the early 1990s (Judd et al 2007;Mitchell et al 1996), and plot studies in several locations have shown that decreases in snowpack lead to soil freezing and increases in nutrient losses Matzner and Borken 2008). While freezing can cause fine root mortality (Cleavitt et al 2008;Tierney et al 2001), alter processes such as litter decomposition (Christenson et al 2010), and increase soil NO 3 -pools (Groffman et al 2001b) and gaseous losses (Groffman et al 2006b), these plot-scale effects of soil freezing do not necessarily translate to higher NO 3 -export at the watershed scale . For example, while plot studies at the HBEF in the White Mountains of New Hampshire, USA showed strong effects of soil freezing on hydrologic and gaseous N 2 O losses Groffman et al 2006b) we were unable to identify the effects of soil freezing in analysis of long-term (40 year) records of N export from experimental watersheds at the HBEF (Fitzhugh et al 2003).…”

Grass litter responses to warming and N addition: temporal variation in the contributions of litter quality and environmental effects to decomposition

“…In the context of climate warming, shorter periods of snow cover can increase soil freezing as a result of reduced insulation (Groffman et al 2001), and exposure to freeze-thaw cycles in the laboratory can accelerate the release of soluble compounds from litter (Melick and Seppelt 1992;Harris and Safford 1996). However, in the field, early snowmelt (Baptist et al 2010) and snow removal (Christenson et al 2010;Kreyling et al 2013) can decrease decomposition rates by increasing the amount of time litter at the soil surface remains frozen, whereas a persistent snowpack can accelerate litter decomposition in late winter by providing a warmer and thermally stable microenvironment (Hu et al 2013;Saccone et al 2013). Nevertheless, in some cases winter warming events have not affected litter decomposition significantly (Walter et al 2013), even when large reductions in faunal decomposers have occurred (Bokhorst et al 2013), and it has been suggested that observations of winter mass loss may result primarily from leaching in autumn, prior to the onset of winter (Bokhorst et al 2010).…”