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Annual and intra-annual water balance components of a short rotation poplar coppice based on sap flow and micrometeorological and hydrological

Fischer, M., Orság, M., Trnka, M., Pohanková, E., Hlavinka, P., Tripathi, A.M., Zalud, Z.
Acta horticulturae 2013 no.991 pp. 401-408
canopy, climate, coppicing, drought, energy balance, evaporation, evapotranspiration, highlands, leaf area index, models, rain, sap flow, soil, stemflow, stomatal conductance, temperature, throughfall, trees, understory, Czech Republic
Comparative measurements of canopy transpiration (T) and evapotranspiration (ET) of a high density poplar stand were conducted in a typical rain-fed area of the Czech Moravian Highlands, Czech Republic, during 2012. Higher mean annual temperature, lower precipitation and period with drought occurred in this year. Sap flow measured on four sample trees was scaled to T and successfully validated by ET measured by Bowen ratio energy balance method. Since the sap flow measurements were available from June to September, a stomatal conductance model and leaf area measurements were used to predict annual T. It was found that when stomatal conductance is scaled to the canopy, a non-linear relationship between LAI and canopy conductance has to be taken into account. An increase of LAI from 0 to 3 had the most important impact on canopy transpiration. Apart from T and ET, interception was assessed by measuring rainfall at open area, canopy throughfall and stemflow. The ET of the understory and soil evaporation was finally estimated as the residual of ET. Maximum daily T and ET was 4.5 and 5.7 mm day-1, respectively, whereas maximum reference evapotranspiration (ETo) was 6.6 mm day-1. Over the entire annual cycle cumulative ET totalled 572 mm, T was 347 mm, soil and understory ET was 176 mm, and interception was 49 mm. Rainfall totalled 568 mm while ETo was 681 mm. The results of this study provide promising material for further up-scaling of poplar short rotation coppice water use in other climatic regions or in future climate conditions.