Tree retention as a conservation measure in clear-cut forests of northern Europe: a review of ecological consequences

Since the mid-1990s, it has been common practice to leave trees for biodiversity purposes when clear-cutting in Finland, Norway and Sweden, and regulations for such tree retention are today included in national legislation and certification standards. Peer-reviewed research publications on tree retention from studies performed in the three countries were analyzed and about 50 relevant biodiversity studies were found, with the first published in 1994. Most studies were directed towards beetles and dead wood, especially high stumps. General conclusions were that retention trees (1) provide some of the substrate types required by early-successional species, (2) alleviate the most serious consequences of clear-cutting on biota, and (3) cannot maintain characteristics of intact mature forests. Larger volumes and more trees tend to maintain diversity better. There is a particular lack of studies on dispersal, landscape effects and long-term dynamics. There is a need to study further the relationship between the biota and the amount of trees, as well as their spatial arrangement. Retention trees should preferably be evaluated in relation to other components in multiscaled conservation, including woodland key habitats and larger protected areas.