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Scaling from single-point sap velocity measurements to stand transpiration in a multispecies deciduous forest: uncertainty sources, stand structure effect, and future scenarios

Hernandez-Santana, Virginia, Hernandez-Hernandez, Adan, Vadeboncoeur, Matthew A., Asbjornsen, Heidi
Canadian journal of forest research = 2015 v.45 no.11 pp. 1489-1497
Acer rubrum, Betula alleghaniensis, Fagus grandifolia, deciduous forests, ecosystem services, forest ecosystems, sap, sapwood, species diversity, stand structure, transpiration, trees, uncertainty, water balance, New Hampshire
A major challenge in studies estimating stand water use in mixed-species forests is how to effectively scale data from individual trees to the stand. This is the case for forest ecosystems in the northeastern USA where differences in water use among species and across different size classes have not been extensively studied, despite their relevance for a wide range of ecosystem services. Our objectives were to assess the importance of different sources of variability on transpiration upscaling and explore the potential impacts of future shifts in species composition on the forest water budget. We measured sap velocity in five tree species (Fagus grandifolia Ehrh., Acer rubrum L., Acersaccharum Marsh., Betula alleghaniensis Britton, and Betulapapyrifera Marsh.) in a mature stand and a young stand in New Hampshire, USA. Our results showed that the greatest potential source of error was radial variability and that tree size was more important than species in determining sap velocity. Total sapwood area was demonstrated to exert a strong controlling influence on transpiration, varying depending on tree size and species. We conclude that the effect of potential species shifts on transpiration will depend on the sap velocity, determined not only by radial variation and tree size, but also by the sapwood area distribution in the stand.