Results of Monitoring at Olkiluoto in 2006 - Environment (pdf) - Posiva

21Biomass of FloraThe biomass of terrestrial vegetation was estimated for the Olkiluoto Biosphere DescriptionReport (Haapanen et al. 2007) by the Finnish Forest Research Institute. Twodifferent ways were used: Stand-based estimation, where the volumes for VCP units by Rautio et al.(2004) were converted to biomass using Biomass Expansion Factors (BEF) byLehtonen et al. (2004a) and understorey biomass models by Muukkonen andMäkipää (2006). Tree-based estimation, where the single tree data measured from the FET plots(Saramäki & Korhonen 2005) was converted to biomasses using models byMarklund (1988), except for fine roots, the biomass of which was calculated accordingto Helmisaari et al. (2007), and for leaves (models created in FFRI byJaakko Repola and Risto Ojansuu). Biomass of coarse roots and stumps of deciduoustrees were estimated using Marklund's (1988) models for pine. The understoreyvegetation coverages of the FEH plots were converted to biomassesusing models created at the Finnish Forest Research Institute (Maija Salemaa).The carbon content of vegetation was assumed to be 50% of dry mass. Net productionof the tree layer was calculated using measured growth estimates (data from Rautio etal. 2004) and BEFs by Lehtonen et al. (2004a). Net production of ground vegetationwas estimated with turnover rates (Muukkonen & Lehtonen 2004). Litter productionestimates are based on turnover rate coefficients of biomass compartments (Lehtonen etal. 2004b, Muukkonen & Lehtonen 2004, Starr et al. 2005, Liski et al. 2006,Muukkonen & Mäkipää 2006).According to the calculations by stands (VCP) the biomass of terrestrial vegetation inthe stands varied between 0.14 and 28.4 kg/m 2 , mean value being 7.3 kg/m 2 . Accordingly,carbon content varied between 0.07 and 14.2 kg/m 2 , and the highest values wereobserved in the Natura conservation area (Fig. 13). The mean carbon content in Scotspine, Norway spruce and deciduous stands was 0.8, 1.2 and 1.5 kg/m 2 , while the maximumcarbon content was 9.1, 9.9 and 11.7 kg/m 2 , respectively. The corresponding valuesfor understorey vegetation were mean 0.13 and maximum 0.32 kg C/m 2 . The totalcarbon content was 24,139 Mg in the terrestrial vegetation of the stands on the OlkiluotoIsland. Based on FET plot measurements, the highest mean carbon content 10.2kg/m 2 was found in 81–100-year-old spruce-dominated forests (Table 10). Mean carboncontent increased from young and infertile sites to more fertile and older ones (Table11). On average, the stem with bark accounted for 43, branches for 22, foliage for 15,stump for 5 and roots for 15% of the total tree biomass on FET plots. The amount ofcarbon bound in ground vegetation was clearly less than in trees (mean value 0.10kg/m 2 , Tables 12 and 13).The combined net production of the trees and understorey vegetation varied from 49 to763 being on average 302 g C/m 2 /a (Fig. 14). Estimates of annual fluxes of net production(growth) and litter production by dominant tree species are presented in Tables 14and 15.