U.S. Department of Energy, Office of Science

Program for Ecosystem Research

Research Project   Effect of warming on the structure and functioning of a boreal black spruce forest ecosystem

Principal investigator:   Stith T. (Tom) Gower

Processes schematic

Processes related to the project goal.

Project goal

Examine how warming the soil and air of a boreal black spruce ecosystem will alter plant phenology, canopy structure, species composition, net primary production, soil surface CO2 efflux, microbial dynamics/composition, and the nitrogen and hydrologic cycles.

Ecosystem being studied

A black spruce plantation within the boreal forest near Thompson, Manitoba, Canada. The boreal forest is one of the largest biomes on earth and may be especially vulnerable to warming because warming has been, and is expected to contiune to be, relatively large at high latitudes.

Results

Warming treatments averaging +5 degrees Celcius over the current air and soil temperatures have been successfully applied throughout 2004 and 2005. While the 2004 growing season had average precipitation, precipitation in 2005 was nearly 3 times the normal average leading to reduced plant water stress. Irrigation to limit soil water differences among treatment plots is working well.

Shoot growth phenology in the air and soil warming treatments started approximately ten days before control treatments in both 2004 and 2005, but ended earlier than control treatments. Therefore, final shoot growth measurements were not different between treatments by the end of the growing season.

No differences were observed for net photosynthesis or needle respiration at their respective treatment temperatures indicating acclimiation to the warming treatment. Similarly, after two full years of treatment no differences in soil CO2 efflux rate have been observed.

Aerial view of study site

Aerial view of the black spruce plantation containing the study plots.

Why this is important

A better quantitative understanding of how boreal forests could respond to warming is needed because boreal forests could become a large source of greenhouse gases with warming. Such a positive feedback to climatic change would exacerbate processes currently driving global warming.

Methods

The study is being conducted in an 18-year-old boreal black spruce (Picea mariana) plantation with understory vegetation and soils characteristic of a regenerating stand following a severe fire. The surrounding natural black spruce forest is 30-years-old with a predominant Vaccinium spp. understory, and a feather moss and sphagnum ground cover. The native soils consist of a 20-30 cm thick surface peat, a 10 cm humus layer, and an underlying sandy loam mineral soil.

Warming of this ecosystem is being facilitated by a combination of above-ground chambers (7.5 m diameter x 10 m tall) superimposed on a 15 x 15 m soil warming plot. A randomized complete block design is being used with four blocks each containing one replicate of the chanbered control, the chambered warming treatment (+5 degrees C), and an ambient reference plot. Warming treatments are ramped up each spring (April) when soil temperatures reach 0 degrees C and ramped down in mid-November. Water is misted into the warming chambers to reduce differences in vapor pressure deficit across treatements.

View of chambers on the site

Chambers in the black spruce plantation.

A range of growth and physiological measurements are being conducted to capture ecosystem responses including: predawn water potential, photosynthesis, soil surface CO2 efflux, foliage and wood respiration, root biomass, canopy phenology, and evapotranspiration.

Further information is available at the project's website.

Personnel

Stith T. Gower, University of Wisconsin

Dustin Bronson, University of Wisconsin

Ingrid VanHerk, University of Wisconsin

Carter DeDolph, University of Wisconsin

Myron Tanner, Univeristy of Wisconsin

Funding period:   April 2002 to present