The scientific work within the activity ''ecological/biological balances and conservation'' is summarised in this report. The aims of the activity during its existence between 1992 and 1994 have been to: i) arrange a workshop and publish the presentations on the environmental aspects of energy forest cultivations, ii) perform joint scientific work together with the activity group on ''biological disposal of wastewaters and sludges'', that is closely related to environmental problems, and iii) produce ecological guidelines concerning energy forestry, suitable for advisers and farmers dealing with bioenergy problems. The most important results from the workshop were the environmental benefits from energy forestry when compared with intensive agriculture and forestry. Energy forestry has positive influence on the carbon balances, nutrient recycling, and soil sustainability. The effects are also positive on the natural flora and fauna, which in most cases are enriched when compared with agricultural crops. From the joint efforts of the two activities the main result was a study tour, conference and workshop, concentrating on biological purification systems. The most promising system seems to be the vegetation filters of short rotation coppice. The report on ecological guidelines contains a number of ideas and recommendations for establishment, management and harvesting of energy forests in an environmentally acceptable way. It gives also advice on how to locate the stands to minimise the risk of nutrient leakage from arable land.