Quantifying the legacy of foliar winter injury on woody aboveground carbon sequestration of red spruce trees

Abstract

Red spruce (Picea rubens Sarg.) decline has been quantitatively attributed to foliar winter injury caused by freezing damage. The results of this injury include foliar mortality, crown deterioration, and negative carbon (C) balances that can lead to tree health declines and eventual mortality. In 2003, a severe region-wide event damaged over 90% of red spruce in the northeastern United States (US). We assessed the influence of the 2003 winter injury event on long-term growth and C sequestration of red spruce trees by measuring the xylem growth (basal area increment) in forest stands in Vermont (VT), New Hampshire (NH), and Massachusetts (MA) where winter injury was quantified in 2003. Although previous work reported 2years of significant linear relationships between winter injury and growth declines, here we show that growth declines relative to pre-injury (average for 2001 and 2002) growth persisted for an additional (third) year. Using 3years of significantly reduced growth, we estimated that the 2003 winter injury event reduced the regional C sequestration of red spruce trees >17.78cm diameter at breast height (DBH) by about 673,000 metric tons (t) of C (approximately 2,465,000 t of CO2) – approximately 70% larger than the previous estimate. Because winter injury in 2003 was positively and significantly related to plot elevation, we also examined relative changes in red spruce growth for three elevation groups: low (<765m), mid- (765–920m) and high (>920m). Relative growth was below pre-injury levels and significantly less for high compared to low elevation groups from 2003 to 2006, after which growth between these groups was indistinguishable through 2010. In 2007, and continuing through 2010, trees in mid-elevation plots exhibited significantly higher growth relative to pre-winter injury levels. Eightyears after the winter injury event, mid-elevation plots had significantly higher net growth than high elevation plots and had rebounded from growth declines following the 2003 winter injury event. As of 2010, trees in the high elevation plots continued to show net C reductions – an enduring legacy of the 2003 winter injury event. The long-lasting reductions in growth subsequent to the 2003 winter injury event were followed by an unprecedented upsurge of growth in recent years, particularly in 2009 and 2010 at mid-elevation plots. This growth increase could reflect the dominance and established ecological niche of red spruce at these elevations, but it could also be influenced by more moderate temperature trends during fall through spring in recent years.