A three decade assessment of climate‐associated changes in forest composition across the north‐eastern USA

Abstract

1. Climate-associated changes in forest composition have been widely reported, particularly where changes in abiotic conditions have resulted in high mortality of sensitive species and have disproportionately favoured certain species better adapted to these newer conditions. In the north-eastern USA and south-eastern Canada, few studies have examined climate-related influences associated with forest composition, and none have considered broad-scale changes over a long temporal (>25 years) period. 2. We used US Forest Service Forest Inventory and Analysis data from 1983 to 2014 across four north-eastern states (Maine, New Hampshire, New York and Vermont) to assess temporal and spatial changes in the occurrence and abundance of American beech Fagus grandifolia Ehrh, sugar maple Acer saccharum L., red maple Acer rubrum L. and birch Betula spp. saplings. We also tested the effects of biotic and abiotic factors on the distribution of the four studied deciduous species over the entire period examined. 3. Occurrence and abundance of American beech have increased substantially over the past three decades, whereas the occurrence and abundance of three other deciduous species have decreased in all ecological provinces of the north-eastern USA, except the Midwest Broadleaf ecological province. Consequently, a clear shift in species composition is currently underway in the beech-maple-birch (BMB) forests of the north-eastern USA, with uncertain consequences for future ecosystem structure and function. 4. In the studied region and over the entire period examined, the distribution of increased occurrence and abundance of beech relative to the three other deciduous species were associated with higher temperature and precipitation as well as higher conspecific basal area and dead tree basal area. 5. Synthesis and applications. The change from beech-maple-birch forests to more beech-dominated forests with beech encroachment to new forest areas across the north-eastern USA may continue if higher intensity harvesting and disturbances (i.e. large-scale canopy openings) do not occur. This would be a significant management concern as beech is associated with a widespread bark disease, is commercially less desirable, and can limit natural regeneration from other species. Our results emphasize the need for management strategies such as higher intensity harvesting methods, vegetation control and limiting browsing pressure to reduce beech dominance.

Divergent responses to climate change and disturbance drive recruitment patterns underlying latitudinal shifts of tree species

“…On the contrary, support for climate change variables mostly outweighed (based on absolute Wald z value) disturbance ones. South of our study area into the United States, climate gradients and their changes were also shown to have impacts on tree range shifts (Bose, Weiskittel, Wagner, & Pauchard, 2017a; Fei et al, ). Interestingly, despite our studying tree species at their northern range limit in eastern North America, greater extension of the growing season did not always lead to a higher probability of sapling recruitment at a site.…”

Half a century of multiple anthropogenic stressors has altered northern forest understory plant communities

“…, Bose et al. , SLU ) and is often accelerated by climate‐change induced increase in forest productivity (Gauthier et al. , Gonsamo et al.…”

“…Forest density is increasing in many northern forest regions (Rautiainen et al 2011, Bose et al 2017, SLU 2017 and is often accelerated by climate-change induced increase in forest productivity (Gauthier et al 2015, Gonsamo et al 2017. Projected increase in productivity under climate warming may also allow further expansion of industrial forestry operations into areas where productivity is currently too low (Raunikar et al 2010).…”

Persistence of balsam fir and black spruce populations in the mixedwood and coniferous bioclimatic domain of eastern North America

“…Also, black spruce benefits more from large fires, owing to its aerial seed bank that persists in serotinous cones remaining in the canopy for many years, until a fire opens them to liberate seeds. If climate change progresses toward warmer conditions with no evidence of dryness (Bose, Weiskittel, & Wagner, ), large fires would be expected to be less frequent, to be replaced with small fires. Also, higher predicted temperatures are expected to stimulate seed supplies (van der Meer, Jorritsma, & Kramer, ; Messaoud, Bergeron, & Asselin, ; Roland, Schmidt, & Johnstone, ).…”

“…Fir expansion would occur through higher seed inputs in the vicinity of balsam fir stands in the coniferous domain. To be effective, balsam fir invasion following small fires would be preceded by its establishment on suitable sites (Bose et al, ). Therefore, the dependence of regeneration on parental trees and site condition, as has been illustrated by the current research, would help to better address real effects of climate change and disturbance on vegetation composition and dynamics in the boreal forest.…”