7.6 Interception of precipitation by a partially harvested MPB infested forest

Thursday, 31 May 2012: 5:00 PM
Alcott Room (Omni Parker House)
David L. Spittlehouse, British Columbia Ministry of Forests, Lands and Natural Resource Operations, Victoria, BC, Canada; and R. Bowler and V. N. Foord

The amount of precipitation intercepted by a forest canopy and evaporated directly back to the atmosphere was determined for a 70-year-old forest where trees had been removed in a 20-m wide strip cut salvage system. All of the dead lodgepole pine trees were removed and the remaining forest strips contained white spruce and subalpine fir trees. The site is a Canadian Carbon Project study site in central British Columbia, Canada. Throughfall of rain was measured using 6-m-long troughs and stem flow with tree collars that directed the water into tipping buckets monitored by a forest weather station. Two 12-point 110-m-long transects were used to gravimetrically determine forest snow pack water equivalent. Rainfall and snowfall were also measured in an adjacent clearcut. Throughfall was 47% of the rainfall for storms of 2.5 mm or less, while above 2.5 mm throughfall = 0.947*Rain-1.22 ±0.6 mm, R2=0.989. Stem flow only occurred for storms > 5 mm, and it was less than 0.1% of the rainfall. Variation in the frequency, duration and intensity of the rain storms and accompanying weather conditions mean that for rain storms above 5 mm interception loss varied by ±50% around the mean. Consequently, canopy interception loss was 30% of the rainfall for a low rainfall summer and 24% for a summer with about a third more rainfall. Interception of snow showed a similar pattern to rainfall with 20% of the precipitation intercepted in a low snowfall winter and only 5% in a high snowfall winter. Forests strips occupy about 50% of the site suggesting site level interception is about half of the value for the forest.
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