U.S. Department of Energy, Office of Science

Program for Ecosystem Research

Research Project   Subalpine and alpine species range shifts with climatic change: temperature and soil moisture manipulations to test species and population responses

Principal investigator:   Lara M. Kueppers

Project goal

Experimentally study the potential for upward migration (i.e., a geographic range shift) of subalpine tree species in response to warming in western mountains, and the alpine species they might replace. Research foci will be on (1) conifer recruitment and alpine plant growth and reproductive output because they are the likely bottlenecks to range shifts in subalpine and alpine environments and (2) the role of population-level adaptation and species-ecosystem interactions in constraining species responses to warming.

Alpine tree line

Snowy alpine tree line in Colorado. Will warming cause trees to migrate upslope (to the left in this photo) and replace existing alpine ecosystems?

Ecosystem being studied

The field experiment will be conducted near the alpine tree line at the Niwot Ridge Long Term Ecological Research Site in Colorado.

Results

The infrastructure needed to conduct the field warming experiments is being constructed at the research site.

Why this is important

An upward migration of subalpine tree species, and the consequent reduction in alpine habitat, would have consequences for many plant and animal species. While models indicate that tree line will rise due to global warming, the probabilities, rates, and extents of such changes have not been experimentally determined, at either the upper or lower range limits of tree line species. The most recent coupled atmosphere-ocean general circulation models project that western North America will warm an average of 1.5-5.0 degrees C by 2100. Moreover, due to the importance of snow albedo feedbacks, regional-scale projections may underestimate warming in some parts of mountainous regions. A warming of 4 degrees C corresponds to nearly 600 m elevation, and would, in effect, move tree line above many peaks in western states.

Results from this work will contribute to a predictive understanding of potential shifts in the geographic distributions of subalpine and alpine species--and the position of the alpine tree line--with warming in the Western United States. Expansion of subalpine conifers into alpine zones could delay snowmelt due to the net effect of shading and albedo, while contraction in the ranges of alpine plants would have consequences for the survival of those species and the survival of animals that depend on them, as well as consequences for alpine recreation activities and water supply.

Methods

The project will combine field manipulations of temperature and moisture across and just above the elevational range of subalpine conifer species with laboratory germination trials and mitochondrial DNA (mtDNA) analysis using conifer seed from throughout the species' North American ranges. Infrared heaters will be used to warm plants and soil (+4.0 to +4.5 degrees C) at sites at three elevations (alpine, tree line, and warm edge of subalpine), with a factorial water addition (to examine the possibility of warming-induced water stress). Conifer seeds of known genetic provenance will be sown into field plots at all three elevations, followed by measurements of demographic and physiological changes and nutrient status of the trees. Additional, analogous field manipulations will be conducted in the alpine without sowing conifer seeds, followed by measurements of demography, physiology, and reproductive output. To test for local climatic adaptation in conifers, climate response curves for distinct populations (determined using mtDNA analysis) will be compared in the field experiments, and from at least 12 populations throughout the species ranges in laboratory germinator experiments.

Personnel

Lara M. Kueppers, University of California, Merced

John Harte, University of California, Berkeley (subaward)

Margaret S. Torn, University of California, Berkeley (subaward)

Jeffrey B. Mitton, University of Colorado (subaward)

Matthew Germino, Idaho State University (unfunded collaborator)

Connie Millar, U.S. Forest Service (unfunded collaborator)

Funding period:   August 2007 to present