Evapotranspiration and canopy characteristics of two lodgepole pine stands following mountain pine beetle attack

Abstract

Abstract:Over the past decade, British Columbia (BC), has experienced the largest mountain pine beetle (MPB) outbreak on record. This study used the eddy-covariance (EC) technique to examine the impact of the MPB attack on evapotranspiration (E) and associated canopy characteristics of two lodgepole pine stands with secondary structure (trees, saplings and seedlings surviving the attack) located in central BC. MPB-06, an 85-year-old almost pure stand of pine trees, was first attacked in 2006, and by 2010,~80% of the trees had been killed. MPB-03, a 110-year-old stand with an overstory consisting of over 90% pine and a developed sub-canopy, was first attacked in 2003 and by 2007 had > 95% pine canopy mortality. EC measurements began in August 2006 at MPB-06 and in March 2007 at MPB-03, and continued for four years. Annual total E ranged from 226 mm to 237 mm at MPB-06, and from 280 to 297 mm at MPB-03, showing relatively little year-to-year change at both sites over the four years. Increased E from the accelerated growth of the surviving vegetation (secondary structure, shrubs and herbs) compensated for reduction in E due to the death of the overstory. Monthly average daytime canopy conductance, the Priestley-Taylor (a), and the canopy-atmosphere decoupling coefficient (Ω) steadily increased during the growing season reaching approximate maximum values of 5 mm s À1, 0.75 and 0.12, respectively. Potential evapotranspiration was approximated using a vapour pressure deficit-dependent a obtained at high soil water content. Calculated water deficits indicated some water-supply limitation to the surviving trees and understory at both sites. Rates of root zone drainage during the growing season were low relative to precipitation.

Implementation of a Marauding Insect Module (MIM, version 1.0) in the Integrated BIosphere Simulator (IBIS, version 2.6b4) dynamic vegetation–land surface model

“…The damage to plants caused by insects, particularly during outbreaks defined by sudden and major changes in insect population, is pervasive in terrestrial ecosystems and affects not only vegetation dynamics but also carbon, nutrient, energy, and water exchanges, and even atmospheric chemistry (Landsberg and Ohmart, 1989;Hunter, 2001;Lovett et al, 2002;Kurz et al, 2008;Amiro et al, 2010;Arneth and Niinemets, 2010;Clark et al, 2010Clark et al, , 2012Stinson et al, 2011;Bowler et al, 2012;Brown et al, 2012Brown et al, , 2014Edburg et al, 2012;Hicke et al, 2012;Yang, 2012; J. Bright et al, 2013;Maness et al, 2013;Mikkelson et al, 2013a;Pugh and Gordon, 2013;Metcalfe et al, 2014;Reed et al, 2014;Seidl et al, 2014;Turcotte et al, 2014;Vanderhoof et al, 2014;Landry and Parrott, 2016).…”

Climate-driven disturbances in the San Juan River sub-basin of the Colorado River

“…Studies pointing towards increased streamflow also broadly found evapotranspiration from the canopy decreased, leading to an increase in runoff. However, work based on observations across scales and encompassing multiple disturbances indicates that the regrowth potential for understory, such as shrubs used in this study, is high and that the regrowth is a major controlling factor for water availability and direction of change for evapotranspiration and runoff (Caldwell et al, 2016;Biederman et al, , 2015Brown et al, 2014;Pribulick et al, 2016). Moreover, ecologists project that global forest covers are expected to decline and be replaced with species and understory compositions that are more water intensive.…”

“…First, replacement of forest with shrubs leads to an increase (relative to the climate-only scenario) in the onthe-ground snow pack accumulation (Fig. 4b), a prominent feature observed in disturbed forests across North America (Boon, 2007;Zou et al, 2010;Biederman et al, 2015;Brown et al, 2014;Harpold et al, 2014). Shrubs in our VIC simulations have no canopy thus they have no mechanism to intercept snow.…”

“…Examination of water partitioning in disturbed forests within time frames of less than 5 years may not adequately resolve effects such as forest succession on the hydrologic regime of study basins (Brown et al, 2005), which can result in a significant overestimation of the impacts of changing forests on water yields over the long term (Pugh and Gordon, 2013). Indeed, most studies that encompass forest disturbance monitoring of greater than 5 years point to increased evapotranspiration from understory regrowth and an associated decline or mitigating effect of the forest cover removal (Brown et al, 2014;Biederman et al, 2014;Guardiola-Claramonte et al, 2011). Other research has shown that vegetation management, such as cutting or thinning of forests in the face of climate change, could be used to ameliorate the impacts of reduced streamflow in the CRB, noting that these effects would only last for a period of approximately 10 years (Zou et al, 2010).…”

Changes in runoff in two neighbouring catchments in the Bohemian Forest related to climate and land cover changes

“…6). In stands killed during the first die-off wave, dense and fastgrowing stand regeneration was increasingly able to compensate for diminished evapotranspiration losses due to mature tree mortality (Brown et al, 2014). Almost a decade later, this recovery was impacted by the second wave of die-off, which hampered a rapid comeback of catchment evapotranspiration to pre-disturbance level.…”