Indicators of biomass and methane yields in vegetated buffer strips

Abstract Searching for available biomasses is a key factor to promote renewable energy, especially biogas. This paper examines the biogas potential of biomass from Danish buffer strips with different types of natural vegetation and the possibility of using the functional trait composition of the vegetation and the nutrient composition of the biomass as indicators for the quantity of the biomass and its biogas potential. Biomass was harvested from 73 plots in 2014 and 2015 and biomass yield, nutrient content (CNP) and methane yields were determined. Prior to harvesting, the plant communities were characterised in terms of species composition, and a cluster analysis was performed to identify species assemblages in terms of vegetation clusters. Four ecologically meaningful clusters were obtained: a tall herb fringe community, a tall grass community, a low herb and grass community and a rich fen/wet meadow community. The biomass yield was numerically higher in the tall herb fringe and the tall grass communities, while the specific methane yield was higher in the tall grass and low herb and grass communities. When all samples were analysed together, the biomass yield was positively correlated with some of the vegetation traits (Ellenberg value soil reaction and leaf dry matter content) and negatively with nitrogen and phosphorus contents in the biomass. In addition, a negative correlation was observed between the biomass yield and the specific methane yield. In contrast, the biomass yield was positively correlated with the methane yield per ha, indicating that even small differences in biomass yield can be more relevant for the methane yield per ha than differences in specific methane yields in natural vegetation. Biomass from tall herb fringe, tall grass and low herb and grass communities is suitable to be incorporated into the anaerobic digestion supply chain; and in these communities it could be possible to predict methane yield per ha, especially in tall grass community, using vegetation traits (Ellenberg values and Grimes life strategy) and phosphorus content in the biomass.