Evapotranspiration in intermediate‐aged and mature fens and upland black spruce boreal forests

Abstract

The Canadian boreal forest consists of a mosaic of landscapes of varying soil drainage and forest age driven by wildfire. The hydrological consequences are complicated by plant responses to soil moisture and forest age, both potentially influencing evapotranspiration. Evapotranspiration was measured using the energy balance residual technique in 2006 and 2007 at forested upland and fen sites that originated following fire in 1964, 1930 and about 1850, near Thompson, Manitoba, Canada. Both net radiation and sensible heat flux density were greater at the older sites than those at the younger sites. Evapotranspiration was also greater at the older sites by between 4 and 19% for the 1930-1964 comparison, and 15% for the 1930-1850 comparison. There was no difference in net radiation between upland and fen sites of the same age, although upland sites had a higher sensible heat flux density. Albedo was greater at the fen sites. Evapotranspiration was greater at the upland sites by 11-20%, likely driven by greater leaf area at the upland sites. These intermediate to mature boreal forest sites still show the persistence of the impact of fire, and it is clear that changes in drainage and local hydrology will also have an impact on local evapotranspiration. The implication is that even these small changes in evapotranspiration can have a great regional and global effect because of the large land area of the boreal forest.

A general predictive model for estimating monthly ecosystem evapotranspiration

“…In addition, measurement errors were possible in even basic landscape-scale hydrological and energy components, such as precipitation and net radiation. Errors for these components can range as high as 9-20% (Barker et al, 2009). Such measurement errors could result in a large uncertainty in estimated monthly P and ET o .…”

“…continuous coverage), but are less reliable in complex stands and small or nonuniform footprints (i.e. canopy gaps) (Wullschleger et al, 1998;Wilson et al, 2001;Ewers et al, 2002;Law et al, 2002;Arain et al, 2003;Paw U, 2006;Ford et al, 2007;Sun et al, 2008aSun et al, , 2009Sun et al, , 2010Barker et al, 2009). Eddy covariance and sapflow methods have gained popularity for simultaneously measuring both water and carbon fluxes because of their ability to resolve fluxes on a short timestep, offering high temporal resolution.…”

Measurement and modelling of bryophyte evaporation in a boreal forest chronosequence

“…Compared to Equation (1), Equation (2) is more physiologically appropriate but required continuous moss moisture level data for field application, whereas Equation (1) (Barker et al, 2009). The resulting models were used to model moss E flux over the course of the growing season.…”

“…Incoming and outgoing photosynthetically active radiation (PAR) were measured above the canopy at each site using LI-190 PAR sensors (LI-COR Inc., Lincoln, NE, USA). Further details on the meteorological stations were given by Barker et al (2009).…”

The Understanding Severe Thunderstorms and Alberta Boundary Layers Experiment (UNSTABLE) 2008

“…Under quiescent atmospheric conditions, the daily contribution of ET to moisture in the convective ABL, primarily through transpiration from vegetation, can exceed that added through advection (Raddatz 2005). Prairie boreal forests typically transpire between 2 and 3 mm day −1 (Amiro et al 2006;Barker et al 2009) compared to wheat crops, which can transpire from less than 1 (water stressed) to more than 7 mm day −1 (very little to no water stress) during the peak senescence period (Raddatz 2005;Brimelow et al 2010). Vegetation (crops and perennial grasses) over most of central and southern Alberta did not experience moisture stress in July 2007, as suggested by the Canadian drought monitoring network (www.agr.gc.ca/pfra/ drought/mapscc_e.htm) (not shown).…”