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Keywords:

  • mountain pine beetle;
  • evapotranspiration;
  • water deficit;
  • canopy conductance;
  • Priestley–Taylor

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 (α), and the canopy–atmosphere decoupling coefficient (Ω) steadily increased during the growing season reaching approximate maximum values of 5 mm s−1, 0.75 and 0.12, respectively. Potential evapotranspiration was approximated using a vapour pressure deficit-dependent α 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. Copyright © 2013 John Wiley & Sons, Ltd.