Tuesday, 3 August 2010: 2:30 PM
Red Cloud Peak (Keystone Resort)
The mountain pine beetle (MPB) has killed more than 675 million m-3 of pine over an area estimated at 16.3 million hectares. This study used the eddy covariance (EC) technique to measure CO2, water vapour and sensible heat exchange above two MPB-attacked lodgepole stands. The first stand, located at Kennedy Siding (MPB-06) (55° 06' 43''N, 122° 50' 23''W) was first attacked in the summer of 2006 and by 2009 <20% of the canopy remained healthy. The second stand, located on the edge of Crooked River Provincial Park (MPB-03) (4° 28' 25''N, 122° 42' 43''W), had secondary structure consisting mainly of spruce trees, and was first attacked in 2003. Over 95% of the pine overstory trees were killed by the beetle when EC measurements began in 2007. MPB-06 was an annual carbon (C) source of 82 and 33 g C m-2 in 2007 and 2008 but became a C sink of 27 g C m-2 in 2009. Gross ecosystem photosynthesis (Pg) was 440, 521 and 550 g C m-2, and ecosystem respiration (R) was 521, 550 and 524 g C m-2 in 2007, 2008 and 2009, respectively. MPB-03 was a C source of 56 g C m-2 in 2007 but was a C sink in 2008 and 2009 of 4 and 11 g C m-2. Pg increased from 432 in 2007 to 515 in 2008 and 540 in 2009, while R was 489, 511 and 526 in 2007, 2008 and 2009, respectively. Net ecosystem productivity (NEP) recovered to C neutrality in the third and fifth year after attack at MPB-06 and at MPB-03, respectively. The recovery at MPB-06 resulted from an increase in photosynthesis by the remaining healthy trees and understory vegetation and at MPB-03 by the secondary structure. In both stands the non-attacked component of the vegetation benefitted from less competition for nutrients and water. In the years following attack there was little change in evapotranspiration (E) at both sites. E ranged from 231 to 240 mm y-1 at MPB-06, and from 286 to 308 mm y-1 at MPB-03, while growing season Priestley-Taylor α averaged 0.53 and 0.49 at MPB-06 and MPB-03, respectively, over the three years. In 2007, 2008, and 2009, values of average growing season water use efficiency were 2.4, 2.7, and 2.7 g C kg-1 H2O at MPB-03, and 1.7, 1.9 and 2.1 g C kg-1 H2O at MPB-06, respectively.
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