Influence of experimental snow removal on root and canopy physiology of sugar maple trees in a northern hardwood forest.

Due to projected increases in winter air temperatures in the northeastern USA over the next 100 years, the snowpack is expected to decrease in depth and duration, thereby increasing soil exposure to freezing air temperatures. To evaluate the potential physiological responses of sugar maple (Acer saccharum Marsh.) to a reduced snowpack, we measured root injury, foliar cation and carbohydrate concentrations, woody shoot carbohydrate levels, and terminal woody shoot lengths of trees in a snow manipulation experiment in New Hampshire, USA. Snow was removed from treatment plots for the first 6 weeks of winter for two consecutive years, resulting in lower soil temperatures to a depth of 50 cm for both winters compared to reference plots with an undisturbed snowpack. Visibly uninjured roots from trees in the snow removal plots had significantly higher (but sub-lethal) levels of relative electrolyte leakage than trees in the reference plots. Foliar calcium: aluminum (Al) molar ratios were significantly lower, and Al concentrations were significantly higher, in trees from snow removal plots than trees from reference plots. Snow removal also reduced terminal shoot growth and increased foliar starch concentrations. Our results are consistent with previous research implicating soil freezing as a cause of soil acidification that leads to soil cation imbalances, but are the first to show that this translates into altered foliar cation pools, and changes in soluble and structural carbon pools in trees. Increased soil freezing due to a reduced snowpack could exacerbate soil cation imbalances already caused by acidic deposition, and have widespread implications for forest health in the northeastern USA.