U.S. Department of Energy, Office of Science

Program for Ecosystem Research

Research Project   Warming-induced biome change at the temperate-boreal ecotone: an experimental test of key regeneration processes

Principal investigator:   Peter B. Reich

Project goal

Assess the potential for projected climatic warming to alter tree species composition at the boreal-temperate forest ecotone by experimentally warming forest plots and documenting effects on establishment and juvenile performance for tree species near their warmer (boreal species) or cooler (temperate species) range limits in northern Minnesota.

Ecosystem being studied

The ecotone between the boreal forest and the temperate forest in northern Minnesota.

The field experiments are being conducted at a relatively "warm lower latitude" site in the Cloquet Forestry Center and at a relatively "cold upper latitude" site in the Hubachek Wilderness Research Center.

Results

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

An hypothesis to be tested is that warming will enhance the growth and survival of seedlings of temperate species at the cold edge of their present range but reduce growth and survival of seedlings of boreal species at the warm edge of their present range. The experimental focus will be on the response of juvenile trees because forest composition in an altered climate likely will depend on the species identity of the individuals that recruit and ultimately replace mature trees as they die in response to disturbance or other natural and induced processes.

Why this is important

Human-induced alteration of earth's climate will undoubtedly result in substantial shifts in species ranges and abundances. The species composition of the southern boreal biome (encompassing much of the northern United States and southern Canada) is likely to be particularly sensitive to future warming because it represents a relatively sharp boundary between many temperate species to the south and boreal species to the north. There is, however, significant uncertainty surrounding the mechanisms of climatic change effects on vegetation compositional change, especially in forests, because of lack of experimental examination of effects of controlled warming.

This project will significantly increase the general understanding of the mechanisms by which climatic warming might cause geographic range shifts of species near their present range boundaries and should aid in specific projections about the potential effects of future warming on the southern boreal forest biome. Such projections are critical to evaluating the role of the region in future feedbacks to regional climatic change, evaluating predictions of regional and global dynamic vegetation models, and informing resource managers and vacationers alike about the ecological (and, by implication, economic) future of the southern boreal biome.

Methods

A vegetation-soil warming experiment is implmented in both understory and open habitats at the two sites in northern Minnesota. The sites lie at different distances to the north of the ecotone between the southern boreal and northern temperate forest biomes. The project is focusing on ten target species, all of which are near their present warm (Pinus banksiana, Picea glauca, Abies balsamea, Populus tremuloides, Betula papyrifera) or cool (Pinus strobus, Quercus macrocarpa, Quercus rubra, Acer rubrum, Acer saccharum) range edge in Minnesota.

Three temperature treatments (ambient, +2.5 degrees C, and +5 degrees C) are imposed using infrared heating lamps augmented with soil heating cables to simultaneously control soil and vegetation (aboveground) temperatures. The three (comparee to the more common two) temperature treatments are used to enable assessment of nonlinear responses to warming. These temperatures bracket the range of anticipated warming in the region during the next 75-100 years.

Measurements will include tree germinant establishment, plant growth, phenology, physiology, and survival; soil, plant, and air temperature; and soil moisture and nutrient status. These measures will be used to assess how germination, growth, and survival at the tree establishment stage might be influenced directly by future warmer or indirectly by warming through the effects of warming on soil resources (including water) and other environmental variables that either directly or indirectly influence plant growth and success.

Personnel

Peter B. Reich, University of Minnesota

Sarah E. Hobbie, University of Minnesota

Rebecca A. Montgomery, University of Minnesota

Jacek Oleksyn, University of Minnesota

Roy A. Rich, University of Minnesota

Funding period:   August 2007 to present