Green tree retention in Fennoscandian forestry

Boreal forest management has changed rapidly during recent years, and new f orestry practices, such as green tree retention (GTR), which aim at ecologi cal sustainability have been developed. With our present knowledge. we cann ot fully assess the ecological benefits of prevailing Fennoscandian GTR lev els(5-10 trees/ha). Small retention tree groups cannot be expected to provi de habitat for interior Forest species because of edge effects. However. ev en individual trees will increase the amount of snags and logs, which are i mportant habitats for many species. According to our own results, the respo nse of understory vegetation depends clearly on retention level. With 7% re tention of stand volume, or about 50 trees per ha, we found no remarkable d ifferences in vegetation response as compared with clear-felling. This indi cates that a higher level of retention is needed to maintain late successio nal 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 ch aracteristics. By locating larger retention tree groups in species-rich are as, and avoiding disturbance to CWD, a higher proportion of the resident sp ecies diversity may be "lifeboated" over the regeneration phase on the stan d level. In this paper we review existing literature on green tree retentio n, with special emphasis on Fennoscandian forest management, biodiversity a nd productivity issues. We present results of two ongoing Finnish experimen tal studies that Focus on the effects of various forestry practices on unde rstory vegetation including epixylic taxa.