A comparison of two methods of estimating transpiration rates from a Sitka spruce plantation |
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| Authors: | R Milne J D Deans E D Ford P G Jarvis J Leverenz D Whitehead |
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| Institution: | (1) Institute of Terrestrial Ecology, Bush Estate, Penicuik, Midlothian, Scotland;(2) Department of Forestry and Natural Resources, University of Edinburgh, Mayfield Road, Edinburgh, Scotland;(3) Present address: College of Forest Resources, University of Washington, Seattle, Washington, USA;(4) Present address: Forest Research Institute, Private Bag, Rotorua, New Zealand |
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| Abstract: | Estimates of hourly transpiration from a 16–17 yr old Sitka spruce forest were calculated from the Penman-Monteith combination equation and compared with estimates from an eddy correlation/energy balance method.Canopy conductances were estimated from stomatal conductances measured using null balance diffusion porometers and took account of canopy variations of stomatal conductance and needle area index.Vertical heat fluxes were measured by the eddy correlation method; transpiration fluxes were then estimated from an energy balance of the forest.There was not a 1:1 relationship between the estimates of transpiration from the two methods. The major sources of error were concluded to be (i) difficulties of estimating the variation in stomatal conductance and leaf area through the canopy, (ii) errors in the value of total leaf area index, and (iii) errors in stomatal conductance measurements.The eddy correlation method was suggested as the more useful for future studies of the variation of forest transpiration in time or space, because the Penman-Monteith equation requires extensive biological measurements. |
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