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Lazarus, Brynne

Rubenstein School of Environment and Natural Resources

2004

M.S.

Red spruce (Picea rubens Sarg.) winter injury is caused by freezing damage that results in late winter reddening and early summer abscission of the most recent foliar age class. Abundant winter injury to the current-year (2002) foliage of red spruce became apparent in the northeastern United States in late winter, 2003. To assess the severity and extent of this damage, we measured foliar winter injury at 28 locations in Vermont and adjacent states and bud mortality at a subset of these sites. Ninety percent of all trees assessed showed some winter injury, and trees lost an average of 46% of a current-year foliage. An average of 32% of buds formed in 2002 were killed in association with winter injury. Both foliar and bud mortality increased with elevation and with crown dominance, and bud mortality increased with greater foliar injury. Foliar injury in 2003 at a plantation near Colebrook, NH, was more than five times typical levels for nine previous years of measurement and more than twice that measured for another high-injury year. Plantation data also indicated that bud mortality in 2003 was greater than previously documented and that repeated winter injury was associated with increased tree mortality. Comparisons of our data with past studies for two native spruce sites also indicated that damage in 2003 was greater than other recently reported high-injury years. Because heavy foliar and bud losses can severely disrupt the carbon economies of trees, the 2003 winter injury event could lead to further spruce decline and mortality, particularly among dominant trees at higher elevations. Understanding the spatial patterns of this injury across the landscape may help support or refute hypotheses regarding causation and highlight areas most at risk for spruce decline and mortality. Relationships between winter injury on dominant and codominant trees and plot elevation, latitude, longitude, slope, and aspect were investigated. Least squares regression showed that injury was greater on west-facing than east-facing plots, was more severe in the western part of the study region, and increased with elevation. Many third and fourth order interactions among the measured variables were also significant using this approach, suggesting the presence of complex spatial relationships. Geographically weighted regression (GWR) was used to examine these relationships. This technique was designed to detect spatial nonstationarity (the variation of parameters over space), and to help distinguish effects that are global in scale from those that show localized patterns. The combined analyses detected the following set of spatial patterns: injury increased with elevation; injury increased from east to west across the study region; injury was greatest on steep slopes at high elevations and on shallower slopes at lower elevations; injury increased with degree to which plots faced west, except at the highest elevations, where injury was uniformly severe; and injury increased with degree to which plots faced south, except at the highest elevations in the northern part of the study region, where injury was uniformly severe. Because injury was greater in areas that historically received greater hydrogen ion inputs -- the western part of the study area, on west-facing slopes, and at higher elevations -- the observed pattern of injury supports the hypothesis that acidic deposition acts on a landscape scale to exacerbate winter injury to red spruce.