Detecting latitudinal range shifts of forest trees in response to recent climate change is difficult because of slow demographic rates and limited dispersal but may be facilitated by spatially compressed climatic zones along elevation gradients in montane environments. We resurveyed forest plots established in 1964 along elevation transects in the Green Mountains (Vermont) to examine whether a shift had occurred in the location of the northern hardwood-boreal forest ecotone (NBE) from 1964 to 2004. We found a 19% increase in dominance of northern hardwoods from 70% in 1964 to 89% in 2004 in the lower half of the NBE. This shift was driven by a decrease (up to 76%) in boreal and increase (up to 16%) in northern hardwood basal area within the lower portions of the ecotone. We used aerial photographs and satellite imagery to estimate a 91-to 119-m upslope shift in the upper limits of the NBE from 1962 to 2005. The upward shift is consistent with regional climatic change during the same period; interpolating climate data to the NBE showed a 1.1°C increase in annual temperature, which would predict a 208-m upslope movement of the ecotone, along with a 34% increase in precipitation. The rapid upward movement of the NBE indicates little inertia to climatically induced range shifts in montane forests; the upslope shift may have been accelerated by high turnover in canopy trees that provided opportunities for ingrowth of lower elevation species. Our results indicate that high-elevation forests may be jeopardized by climate change sooner than anticipated.climate change ͉ range shift G lobal climate is currently warming at an unprecedented rate with potentially profound and widespread effects on the distributions of ecological communities. Mean global temperature rose by 0.6°C over the past century, the rate of warming since 1976 has been greater than any other period during the last 1,000 years, and the decade 1990-1999 was the hottest in recorded history (1, 2). Recent climate change has been driven primarily by anthropogenic emissions of greenhouse gases (GHG), and warming is likely to continue at the same or an accelerated rate for the foreseeable future (3-6): global temperatures are predicted to rise by another 1.4-5.8°C by the year 2100 (7). Climate is an important determinant of species' ranges, and rising temperatures associated with GHG emissions are predicted to lead to species' migrations poleward or upward in elevation (8-10). Climate-linked range shifts have already been observed in some taxa (11,12). Although forest composition and geographic distributions of canopy trees are expected to shift with global warming, it is not clear what level of inertia, or time lag, forests will display to climatic forcing nor how strong the relationship will be between warming and tree line rise (13-15). Historical reconstructions and models of forest response to climate change suggest that the natural pace of tree recruitment and canopy turnover result in century-scale responses of ecotones to climate change, which could ma...

In September 2017, Irma became the first recorded category 5 hurricane to hit the Caribbean Windward Islands. The second category 5, Maria, followed two weeks later. In November 2017, we assessed the structural impact of this disturbance on highly valued Caribbean forest ecosystems. We recorded the status of 935 tree stems on Saba and St. Eustatius in stands at different elevations. Tree damage was substantial on both islands, with 93 percent of stems being defoliated, 84 percent having lost primary and/or secondary branches and 36 percent having structural stem damage. Average tree mortality was 18 percent, with mortality being nearly twice as high on St. Eustatius than on Saba. Surprisingly, we found that neither individual stem size nor community size distributions mediated the forests’ response to the hurricanes. Our results show that these hurricanes comprised a density‐independent disturbance, which may become more common as the frequency of strong hurricanes is projected to increase.

No abstract

Global change may induce shifts in plant community distributions at multiple spatial scales. At the ecosystem scale, such shifts may result in movement of ecotones or vegetation boundaries. Most indicators for ecosystem change require timeseries data, but here a new method is proposed enabling inference of vegetation boundary movement from one 'snapshot' (e.g. an aerial photograph or satellite image) in time. The method compares the average spatial position of frontrunners of both communities along the vegetation boundary. Mathematical analyses and simulation modeling show that the average frontrunner position of retreating communities is always farther away from a so-called optimal vegetation boundary as compared to that of the expanding community. This feature does not depend on assumptions about plant dispersal or competition characteristics. The method is tested with snapshot data of a northern hardwood-boreal forest mountain ecotone in Vermont, a forest-mire ecotone in New Zealand and a subalpine treeline-tundra ecotone in Montana. The direction of vegetation boundary movement is accurately predicted for these case studies, but we also discuss potential caveats. With the availability of snapshot data rapidly increasing, the method may provide an easy tool to assess vegetation boundary movement and hence ecosystem responses to changing environmental conditions.

No abstract