WATER CONSUMPTION AND BIOMASS YIELDS RELATION IN SHORT ROTATION POPLAR COPPICE

The plantations of short rotation coppice (SRC) usually based on poplar or willow species are promising source of biomass for energy use. To contribute to decision-making process where to establish the plantations we evaluated the water consumption and its relation to biomass yields of poplar hybrid clone (Populus nigra x P. maximowiczii) in representative conditions for Czech-Moravian Highlands. Water availability is usually considered as the main constraint of well profiting SRC culture and therefore we focused on analyzing the linkage between the aboveground biomass increments and the total stand evapotranspiration (ET) and thus on so called water use efficiency (WUE). During the seasons 2008 and 2009 the total stand ET measured by Bowen ratio system constructed above poplar canopy and the stem diameter increments of randomly chosen sample trees were examined. The stem diameters were subsequently converted to total above ground biomass by allometric equation obtained by destructive analysis at the beginning of 2010. The biomass volume and its increment of particular trees were subsequently transformed to the whole canopy growth and correlated with the ET values. Our results revealed that there was a statistically significant relation between water lost and biomass growth with coefficients of determination r(2) 0.96 and 0.57 in 2008 and 2009 respectively. The dynamic of seasonal WUE varied from 4 to 0 g kg(-1) and from 6 to 0 g kg(-1) with means 2.8 and 3.4 g kg(-1) in both executed years respectively. These values are comparable with other broadleaved tree species of temperate climate zone and suggest that economically profitable plantation (defined by yield at least in the range of 10 - 12 Mg ha(-1) year-1 of dry matter content) will consume more than 400 - 450 mm per year and thus will demand a locality with higher and adequately temporally distributed amount of precipitation especially in rain feed areas such as the discussed Czech-Moravian Highlands.