Abstract
The authors have developed a scaling approach to aggregate tree sap flux with reduced error propagation in modeled estimates of actual transpiration () of three boreal species. The approach covers three scales: tree point, single tree trunk, and plot scale. Throughout the development of this approach the error propagated from one scale to the next was reduced by analyzing the main sources of error and exploring how some field and lab techniques, and mathematical modeling can potentially reduce the error on measured or estimated parameters. Field measurements of tree sap flux at the tree point scale are used to obtain canopy transpiration estimates at the plot scale in combination with allometric correlations of sapwood depth (measured microscopically and scaled to plots), sapwood area, and leaf area index. We compared the final estimates to actual evapotranspiration and actual transpiration calculated with the Penman–Monteith equation, and the modified Penman–Monteith equation, respectively, at the plot scale. The scaled canopy transpiration represented a significant fraction of the forest evapotranspiration, which was always greater than 70%. To understand climate change impacts in forested areas, more accurate actual transpiration estimates are necessary. We suggest our model as a suitable approach to obtain reliable estimates in forested areas with low tree diversity.
Highlights
Climate change is reflected in almost every ecosystem by rising temperatures and changing precipitation patterns [1]
These canopy actual transpiration estimates are compared to actual evapotranspiration (E ) and actual transpiration values calculated with the Penman–Monteith equation, and the modified Penman–Monteith equation, respectively
Since the determination of LAIu and Ωu was essentially based on previous reports, which at the same time are based on a few assumptions, it was necessary to observe the influence of LAIu and
Summary
Climate change is reflected in almost every ecosystem by rising temperatures and changing precipitation patterns [1]. Higher seasonal temperatures in the boreal forest will increase evapotranspiration rates, decrease groundwater recharge, and affect water runoff levels [2,3,4]. Evaporation and transpiration are two water balance components whose estimates are well known to carry uncertainty due to the use of equations and models that (1) lump the components into a single estimate of evapotranspiration (ET), and (2) focus on estimating ET under ideal atmospheric conditions and with an unlimited source of water (i.e., potential ET) [8,9]. This paper focuses on estimating actual transpiration (Tplot ) and actual ET (Ea ) as a first step to reduce the uncertainty introduced by assumptions of ideal conditions
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