Boreal Ecosystem Research and Monitoring Sites

Evapotranspiration at the Old Aspen and Old Black Spruce Sites

Jilmarie Stephens^a, Nicholas Grant^a, Zoran Nesic^a, Paul Jassal^a, Andy Black^a, and Greg Neufeld^b

^a Biometeorology and Soil Physics Group, University of British Columbia, Vancouver ,BC
^b Eagle Bay Resort, East Trout Lake, Saskatchewan

Boreal forest accounts for 30% of the Canadian landscape and plays an important role in the global carbon and water cycles. How these processes will change with respect to climatic variability is poorly understood. Our goal is to improve our understanding of the integrated system response (climate, hydrology, soil and vegetation) of the southern boreal forest to variation in climate.

Black spruce forests occupy 39% of the area of North American boreal forest and are the climax vegetation for these forests. Aspen forests occupy 21% and are particularly dynamic in their carbon and energy exchange because of the seasonal change in leaf area index (Black et al., 2005). Hence they are important to our understanding of the response of the boreal forest to climate change.

Old Black Spruce and Old Aspen were established in 1993 as part of the Boreal Ecosystem-Atmosphere Study (BOREAS) and eddy-covariance (EC) flux measurements were first made during 1994 and 1996. Continuous measurements have been made since 1996 at Old Aspen and 1999 at Old Black Spruce as part of Boreal Ecosystem Research and Monitoring Sites (BERMS) and Fluxnet Canada/CCP. In 2013 the research at the sites became a part of the Changing Cold Regions Network (CCRN). As their names suggest, each site is dominated by a particular mature tree species, ranging in age from about 50-150 years.

Scaffold flux tower at OA

OBS eddy covariance array.

We have high-quality year-round EC measurements of evapotranspiration (E), and related micrometeorological fluxes of momentum, sensible heat, and CO₂. In addition we measure climate variables (precipitation, barometric pressure, radiation components, air and soil temperature, soil moisture content, relative humidity, and wind speed, etc.). The majority of the instrumentation used to record these measurements are mounted on double scaffold towers, which range in height from 2-35m. The towers provide an excellent platform to measure variables at various heights within and above the forest.  We carry out QA/QC and archive and gap fill these data , synthesize the results to determine trends in climate and fluxes, and identify linkages between E, net (NEP) and gross (GEP) ecosystem productivity, water use efficiency (WUE) and environmental stresses.

Our research goals are to continue to make EC and climate measurements at OA and OBS. We plan to obtain key surface E characteristics including the aerodynamic and surface conductances,

Mature aspen canopy at OA.

the McNaughton-Jarvis decoupling factor and the Priestley-Taylor α, and parameterize them using environmental variables (Brümmer et al., 2012). We hope to account for the spatial heterogeneity in vegetation and energy and water balances in relation to topography and soils. We also would like to evaluate the relative merits of using three remote-sensing approaches to estimate landscape E.

The Old Aspen site is located near the south end of Prince Albert National Park, Saskatchewan.The forest consists of  trembling aspen, Populus tremuloides Michx. with scattered balsam poplar, Populus balsamifera L. and hazelnut, Corylus cornuta Marsh. understorey.

Mature black spruce canopy at OBS

The Old Black Spruce site is located approximately 100 km NE of Prince Albert, Saskatchewan near White Swan Lake. The forest is dominated by black spruce (Picea mariana), with sparsely distributed tamarack (Larix laricina Du Roi).