Sugar maple’s important ecological and economic role in northeastern forests has made it one of the best-studied species in eastern North America, but many questions remain about the potential drivers of recent sugar maple decline. While many note the likely influence of a changing climate on sugar, identifying the relationships among long-term climate records and sugar maple condition have been elusive. In order to better understand which climate characteristics influence sugar maple condition, we compared annual sugar maple crown condition metrics from over two decades of long-term forest health field monitoring to a suite of ecologically relevant climate metrics calculated using downscaled climate data. These relationships were then used to examine spatial and temporal variability in historical climate induced decline, and use high resolution climate projections to better understand the potential impact of ongoing climate change on sugar maple health.
By removing the influence of disturbance events during this time period to isolate the impact of climate, five climate metrics were identified that were significantly related to sugar maple decline. While three of these are the monthly based metrics commonly used in climate analyses (minimum April, August and October temperatures), two are novel metrics designed to capture extreme climate events (periods of unusual warmth in January and August). The climate-driven variability in canopy condition that we detected is comparable to the variability introduced by defoliation and other disturbance events, indicating that climate conditions, though rarely included in sugar maple decline studies, may be of equal importance as more traditionally studied stress agents.
Modeled across the state, results indicate that ongoing changes in climatic conditions have been detrimental to sugar maple health over the study period, and are likely to degrade further over time. Climate projections under a low emissions scenario indicated that 35% of sugar maples across the state would likely experience moderate to severe climate-driven decline by 2051, increasing to 55% by 2071. Under a high emissions scenario, this climate-driven decline increases to 84% of sugar maples by 2071. However, geographic variability in projected climate-driven decline indicates that, while conditions for sugar maple will deteriorate across the state, climate refugia should also be available to maintain sugar maple in spite of changing climatic conditions. Considering the predominant role of sugar maple in Vermont’s economy and culture, managing this resource into the future as climate changes is of great concern and could pose a considerable challenge.