Green Tree Retention in Fennoscandian Forestry

Boreal forest management has changed rapidly during recent years, and new forestry practices, such as green tree retention (GTR), which aim at ecological sustainability have been developed. With our present knowledge, we cannot fully assess the ecological benefits of prevailing Fennoscandian GTR levels (5-10 trees/ha). Small retention tree groups cannot be expected to provide habitat for interior forest species because of edge effects. However, even individual trees will increase the amount of snags and logs, which are important habitats for many species. According to our own results, the response of understory vegetation depends clearly on retention level. With 7% retention of stand volume, or about 50 trees per ha, we found no remarkable differences in vegetation response as compared with clear-felling. This indicates that a higher level of retention is needed to maintain late successional plant species on the site. Our data also show that there is much within-stand type variation, which correlates with the amount of CWD and stand characteristics. By locating larger retention tree groups in species-rich areas, and avoiding disturbance to CWD, a higher proportion of the resident species diversity may be ''lifeboated'' over the regeneration phase on the stand level. In this paper we review existing literature on green tree retention, with special emphasis on Fennoscandian forest management, biodiversity and productivity issues. We present results of two ongoing Finnish experimental studies that focus on the effects of various forestry practices on understory vegetation including epixylic taxa.