Sugar Maple Trees at the Hubbard Brook Experimental Forest
US Forest Service
81 Carrigan Drive, Burlington, VT 05405
phone: (802) 656-1715
Department of Biology, Boston University
5 Cummington Street, Boston, MA 02215
phone: (617) 353-6978
PROJECTED INCREASES in winter air temperatures over the next 100 years are expected to decrease the depth and duration of snowpack in the northeastern U.S., thereby increasing soil exposure to freezing air temperatures. Past research at the Hubbard Brook Experimental Forest (HBEF) has used experimental snowpack reduction (via shoveling of early winter snow accumulation) to show that reduced snowpack does increase soil freezing (Groffman et al. 2001), that this freezing can injure sugar maple tree roots (Tierney et al. 2001), and lead to soil nitrate increases that induce soil acidification, calcium (Ca) leaching and aluminum (Al) mobilization (Fitzhugh et al. 2001, 2003). However, no research has been conducted to evaluate if these changes in root and soil processes lead to changes in the foliar cations and carbohydrates, and woody shoot elongation.
To evaluate the physiological responses of sugar maple trees to a reduced snowpack, we measured root injury, foliar cation and carbohydrate concentrations, woody shoot carbohydrate levels, and woody shoot growth of trees in a snow reduction experiment at the HBEF. Snow was removed from treatment plots for the first six 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 snow removal plots had significantly higher (but sub-lethal) levels of electrolyte leakage (a measure of cell membrane damage) than trees in reference plots. Foliar Ca:Al 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 woody shoot growth and increased foliar starch concentrations. We propose that impaired Ca and Al nutrition reduced shoot growth (Figure 1), and that this then led to buildups of foliar starch (Figure 2). Our results are consistent with previous research implicating soil freezing as a cause of soil acidification that leads to soil cation imbalances, and are the first to show that this translates into altered foliar cation pools, and changes in structural and soluble carbon in maple trees (Comerford et al. 2012). Increased soil freezing due to a reduced snowpack could exacerbate existing soil cation imbalances caused by acidic deposition and have widespread implications for forest health.
Some Methods Used
Four replicate of 13 m x 13 m snow removal (shoveled) and reference (not shoveled) plots were established in 2007 (Templer et al. 2012). Beginning in December 2008 and 2009, snow was removed via shoveling for 6 weeks from the 4 treatment plots. For all plots, the depth of snowpack was monitored (Templer et al. 2012) and soil temperature was measured at 6 depths (1, 3, 7, 15, 30 and 50 cm deep) below the forest floor (Comerford et al. 2012).
In April 2010, fine roots (< 2 mm in diameter) were collected from soils adjacent to 3 sugar maple trees per plot (Figure 3). In July 2010, woody shoots and foliage was collected from these sample trees (Figure 4). Shoots were used to assess the 2010 growth of terminals (mm) and measure soluble carbohydrate (sugars and starch) concentrations in wood. Foliage was used to measure the cation nutrition and soluble carbohydrate concentrations in leaves (Comerford et al. 2012).
ReferencesComerford DP, Schaberg PG, Templer PH, Socci AM, Campbell JL, Wallin KF 2012 Influence of experimental snow removal on root and canopy physiology of sugar maple trees in a northern hardwood forest. Oecologia DOI 10.1007/s00442-012-2393-x
Fitzhugh RD, Driscoll CT, Groffman PM, Tierney GL, Fahey TJ, Hardy JP 2001 Effects of soil freezing disturbance on soil solution nitrogen, phosphorus, and carbon chemistry in a northern hardwood ecosystem. Biogeochemistry 56:215-238
Fitzhugh RD, Driscoll CT, Groffman PM, Tierney GL, Fahey TJ, Hardy JP 2003 Soil freezing and the acid-base chemistry of soil solutions in a northern hardwood forest. Soil Science Society of America Journal 67:1897-1908
Groffman PM, Driscoll CT, Fahey TJ, Hardy JP, Fitzhugh RD, Tierney GL 2001 Colder soils in a warmer world: A snow manipulation study in a northern hardwood forest ecosystem. Biogeochemistry 56:135-150
Templer PH, Schiller AF, Fuller NW, Socci AM, Campbell JL, Drake JE, Kunz TH. 2012 Impact of a reduced winter snowpack on litter athropod abundance and diversity in a northern hardwood forest ecosystem. Biology and Fertility of Soils 48: 413-424
Tierney GL, Fahey TJ, Groffman PM, Hardy JP, Fitzhugh,RD, Driscoll CT 2001 Soil freezing alters fine root dynamics in a northern hardwood forest. Biogeochemistry 56:175-190
Yanai R, Fisk M, Fahey T, Cleavitt N, Park B 2008) Identifying roots of northern hardwood species: patterns with diameter and depth. Canadian Journal of Forest Resources 38:2862-2869
Date Prepared: July 2012