Colder soils in a warmer world: A snow manipulation study in a northern hardwood forest ecosystem

In this special section of Biogeochemistry, we present results from a snow manipulation experiment in the northern hardwood forest ecosystem at the Hubbard Brook Experimental Forest in the White Mountains of New Hampshire, U.S.A. Snow is important as an insulator of forest soils. Later development of snowpacks, as may occur in a warmer climate, may result in increases in soil freezing (i.e. colder soils in a warmer world) and could cause changes in fine root and microbial mortality, hydrologic and gaseous losses of nitrogen (N), and the acid-base status of drainage water. In our study, we kept soils snow free by shoveling until early February during the mild winters of 1997/1998 and 1998/1999. The treatment produced mild, but persistent soil freezing and induced surprisingly significant effects on root mortality, soil nitrate (NO₃^-) levels and hydrologic fluxes of C, N and P. In this special section we present four papers addressing, (1) soil temperature and moisture response to our snow manipulation treatment (Hardy et al.), (2) the response of fine root dynamics to treatment (Tierney et al.), (3) the response of soil inorganic N levels, in situ N mineralization and nitrification, denitrification and microbial biomass to the treatment (Groffman et al.) and (4) soil solution concentrations and fluxes of C, N and P (Fitzhugh et al.). In this introductory paper we: (1) review the literature on snow effects on forest biogeochemistry, (2) introduce our manipulation experiment and (3) summarize the results presented in the other papers in this issue.