AN ASSESSMENT OF RETENTION TREES IN HYLOCOMIOSA FOREST TYPE IN SOUTHERN LATVIA

Abstract

In Latvia the forest legislation requires that at least five living trees must be retained per hectare after clear-cutting. It is known that retention trees significantly increase the biodiversity in production forest landscape. After clear-cutting retention trees function as habitats for various lichens, mosses, insects, fungi and birds. Over time retention trees are incorporated into the young forests stand and provide presence of old trees, which is necessary for many endangered and rare species. After the death, these trees turn into coarse woody debris which is an essential habitat and feeding source for many taxa. However, the conservation and mortality of the retention trees has not been studied extensively because this approach has been established recently. The aim of this study was to evaluate development of the retention trees in Hylocomiosa type of forests in Southern Latvia. In total 12 young forest stands were surveyed in 2009 and 2015. The total area – 13.7 ha, on average forest stand size varies from 0.5 to 3.0 ha. All the studied sites were harvested in 2002, 2004, 2006 and 2008. All measurements of tree species, height, and diameter and defoliation class assessed and the status of tree (growing tree, coarse woody debris – snags, stems and downed logs) was indicated. Results show that after the studied period of seven years 24 retention trees died. Average level of the tree mortality is 15 %. The mortality level of Scots pine retention trees is 5.8 %, for aspen – 50 % and that for birch – 92.3 %. An average it is 8.5 green retention trees per 1 ha of young stand (22.9 m3 ha-1). On average 2.3 pieces coarse woody debris are per 1 ha of young stand (3.52 m3 ha-1), mostly - aspen wood (2.4 m3 ha-1). Woody debris of the young stands is divided to the first 4 decay levels according to classification (Stokland et al., 2001). 50 % of the listed woody debris is related to the 3rd decay level which means that woody debris is moderately decomposed.