Unexpected Expansion of Spruce and Fir Varies at Ecotones Across the Eastern US
Abstract
Forest species are widely expected to respond to climate variability and change by migrating or shifting ranges to track favorable climatic conditions, but the pace of change is unknown, and predictions don't hold up consistently when confronted with empirical data. Recent studies reveal a complicated range of responses to contemporary climatic change; tree species have demonstrated a failure to migrate, range contractions when "leading-edge" shifts were expected or even "trailing-edge" range expansions to lower and warmer elevations. Subalpine forests in particular are predicted to track climate change by retreating upslope, but recent reports of unexpected forest dynamics, including spruce-fir forest expansion over 30 years of contemporary climate change, show that our understanding of montane systems is insufficient. Multiple lines of evidence now point to increasing growth and canopy recruitment of spruce (Picea) and fir (Abies) species that occur at high elevations and favor cooler climates. But increased growth and recruitment is not happening everywhere. Rather, in the northern and central Appalachians, from Maine to West Virginia, these directional changes are strongest at mid-elevation ecotones, where spruce-fir dominance gives way to deciduous species from lower elevations. Spruce-fir forests above the subalpine ecotone and in the southern Appalachians show more variable trends. We measured these phenomena with wall-to-wall time series from the Landsat archive in Google Earth Engine, plot-, and other data and tested whether shifts at the spruce-fir ecotone were driven by land use, forest policy, stand dynamics, disturbance, changes in climate, and changes in atmospheric deposition using hierarchical models. Here, we analyze these data together for the first time to quantify the extent to which spruce-fir abundance has changed in and above the subalpine ecotone and to deduce the mechanisms responsible for these unexpected changes.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2018
- Bibcode:
- 2018AGUFM.B21B..07F
- Keywords:
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- 0414 Biogeochemical cycles;
- processes;
- and modeling;
- BIOGEOSCIENCESDE: 0428 Carbon cycling;
- BIOGEOSCIENCESDE: 0439 Ecosystems;
- structure and dynamics;
- BIOGEOSCIENCESDE: 1630 Impacts of global change;
- GLOBAL CHANGE