Evaluating degradation in a North American temperate forest

Forest degradation has been a focus of recent concern, especially in tropical countries, but temperate forests may also exhibit degradation. Our analysis of USDA Forest Service Forest Inventory and Analysis data shows that nearly 40% of the forestland in northern New England, USA, (Maine, New Hampshire, and Vermont) is in an understocked condition when species desirability and tree form are considered. This understocked area does not contain sufficient stand-level density of current or potential future sawlog trees, of preferred or secondary commercial species, to be able to fully utilize the growing space of the site following 10 years' growth (i.e., they are below the “C-line” in a stand stocking guide when desirable trees are considered). Although forests in the region show a slight trend of increased stocking, nearly all this increase comes from shade-tolerant hardwoods (e.g. Fagus grandifolia), trees with poor form (e.g. Acer rubrum), and from Abies balsamea which is subject to episodic eastern spruce budworm (Choristoneura fumiferana) outbreaks. This degraded condition is likely the result of past management activities that have not considered long-term silvicultural objectives and may entail reduced resilience to many climate-related risks for forests and the ecosystem services they provide. Forest management and policy alternatives must be designed and incentivized to restore forest productivity and diversity and to increase climate resilience of the forests in northern New England.