EFFECTS OF ENERGY FORESTRY ON SOILS

The effects of energy forestry on former arable soils are summarized based on our own data from interdisciplinary field experiments as well as on literature published. The present results show that soil physical properties are influenced positively due to the lack of frequent input of heavy agricultural machinery. To what extent intensive harvesting effects may deteriorate soil structure and cause overcompactions with negative consequences for tree growth and ecological functions of soils, needs further attention. Soil solution nitrate can significantly be reduced in soils planted with fast growing trees, as long as nitrogen fertilizers pre applied in accord with the nutrient demands of the trees. The ground vegetation may also act as an important nitrogen sink during plantation establishment and after harvesting. During the first phase after afforestation an enhanced mobilization of easily decomposable above ground and root litter residues takes place. Subsequently the carbon and nitrogen contents of afforrested soils increase in the long term mainly due to the lack of frequent soil cultivation. Among soil organisms, microbial biomass and most faunal groups, especially decomposers, are advanced under tree plantations. The diversity of soil fauna is generally increased compared to arable land. From the viewpoint of soil science general ecological criteria have to be considered in intensive forest land use systems. An entire and holistic view of the ecological consequences of energy forestry is necessary especially with respect to the long term, and to make forest biomass comparable and competitive with fossil fuels. There is a need for future research, which should include important chemical, physical and biological elements or processes in soils.