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A rapid upward shift of a forest ecotone during 40 years of warming in the Green Mountains of Vermont

  1. Brian Beckage * , † ,
  2. Ben Osborne *,
  3. Daniel G. Gavin * , ‡ ,
  4. Carolyn Pucko *,
  5. Thomas Siccama § , and
  6. Timothy Perkins
  1. *Department of Plant Biology, University of Vermont, Burlington, VT 05405;
  2. §School of Forestry and Environmental Studies, Yale University, New Haven, CT 06511; and
  3. Proctor Maple Research Center, University of Vermont, Underhill Center, VT 05490

  1. Edited by Christopher B. Field, Carnegie Institution of Washington, Stanford, CA, and approved December 21, 2007 (received for review September 21, 2007)

Abstract

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.

Footnotes

  • †To whom correspondence should be addressed. E-mail: brian.beckage{at}uvm.edu

  • Author contributions: B.B. designed research; B.B., B.O., C.P., T.S., and T.P. performed research; B.B. and B.O. analyzed data; and B.B., B.O., and D.G.G. wrote the paper.

  • ↵ ‡Present address: Department of Geography, University of Oregon, Eugene, OR 97403.

  • The authors declare no conflict of interest.

  • This article is a PNAS Direct Submission.

  • This article contains supporting information online at www.pnas.org/cgi/content/full/0708921105/DC1.

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