Raul Rosenvald

Can retention forestry help conserve biodiversity? A meta-analysis

Industrial forestry typically leads to a simplified forest structure and altered species composition. Retention of trees at harvest was introduced about 25 years ago to mitigate negative impacts on biodiversity, mainly from clearcutting, and is now widely practiced in boreal and temperate regions. Despite numerous studies on response of flora and fauna to retention, no comprehensive review has summarized its effects on biodiversity in comparison to clearcuts as well as un-harvested forests. Using a systematic review protocol, we completed a meta-analysis of 78 studies including 944 comparisons of biodiversity between retention cuts and either clearcuts or un-harvested forests, with the main objective of assessing whether retention forestry helps, at least in the short term, to moderate the negative effects of clearcutting on flora and fauna. Retention cuts supported higher richness and a greater abundance of forest species than clearcuts as well as higher richness and abundance of open-habitat species than un-harvested forests. For all species taken together (i.e. forest species, open-habitat species, generalist species and unclassified species), richness was higher in retention cuts than in clearcuts. Retention cuts had negative impacts on some species compared to un-harvested forest, indicating that certain forest-interior species may not survive in retention cuts. Similarly, retention cuts were less suitable for some open-habitat species compared with clearcuts. Positive effects of retention cuts on richness of forest species increased with proportion of retained trees and time since harvest, but there were not enough data to analyse possible threshold effects, that is, levels at which effects on biodiversity diminish. Spatial arrangement of the trees (aggregated vs. dispersed) had no effect on either forest species or open-habitat species, although limited data may have hindered our capacity to identify responses. Results for different comparisons were largely consistent among taxonomic groups for forest and open-habitat species, respectively. Synthesis and applications. Our meta-analysis provides support for wider use of retention forestry since it moderates negative harvesting impacts on biodiversity. Hence, it is a promising approach for integrating biodiversity conservation and production forestry, although identifying optimal solutions between these two goals may need further attention. Nevertheless, retention forestry will not substitute for conservation actions targeting certain highly specialized species associated with forest-interior or open-habitat conditions. Our meta-analysis provides support for wider use of retention forestry since it moderates negative harvesting impacts on biodiversity. Hence, it is a promising approach for integrating biodiversity conservation and production forestry, although identifying optimal solutions between these two goals may need further attention. Nevertheless, retention forestry will not substitute for conservation actions targeting certain highly specialized species associated with forest-interior or open-habitat conditions.

Nesting of the black stork (Ciconia nigra) and white-tailed eagle (Haliaeetus albicilla) in relation to forest management

Since 1957, 200 m zones around known nests of the black stork (Ciconia nigra) and white-tailed eagle (Haliaeetus albicilla) have been strictly protected in Estonia. Yet, the black stork population has recently suffered a large decline, which coincides with the intensification of forestry. To check whether higher disturbance levels could have caused the decline, we related the extent of forestry operations and mature forest near black stork nests to their occupancy, treating the increasing eagle population as a comparison. For both species, we studied 1 km zone around 38 nest sites and, for each nest site, around two random points 2 km away. The total annually cut and reforested area was used to quantify forestry activity, since this single variable explained most of the variability in the extent of different forestry operations. Management was significantly more extensive in the landscapes inhabited by black storks than those inhabited by white-tailed eagles, but the periods of nest occupancy and unoccupancy did not differ significantly in either species. There were neither species-specific nor occupancy-related differences in the total area of mature forest. We conclude that, compared with the white-tailed eagle, the black stork is more vulnerable to disturbance and landscape change due to forestry operations, but these processes are probably not responsible for the recent decline of the stork population.

Density and Diversity of Hole-Nesting Passerines: Dependence on the Characteristics of Cavities

Abstract. In addition to the well-known limiting effect of cavity abundance on the density of hole-nesting passerines, other aspects of cavity availability may shape their communities as well. Notably, where there is a considerable aggregation of cavities, territory-holders may prevent the occupation of the nearest cavities by other birds, whereas a supply of diverse cavities may reduce interspecific competition. We used multivariate general linear models to explore whether, and how, variables describing the supply of small cavities are related to the density and diversity of hole-nesting passerine communities in 33 hemiboreal old forest stands. The total density of 12 species (1.3 ± 0.8 pairs/ha) increased with cavity density and diversity, but was not affected by cavity aggregation. As expected, cavity diversity also promoted bird diversity; indeed, the densities of different species were positively related to the densities of different cavity types. The results indicate that segregation in nest-cavity selection affects the co-occurrence of passerine species and, at the mean densities of small tree-cavities in the region (2.3/ha), cavity aggregation does not markedly reduce their availability. In conservation management, therefore, it is important to maintain a diverse supply of cavities in addition to their abundance, in order to sustain hole-nester communities.

Have recent changes in forest structure reduced the Estonian black stork Ciconia nigra population

The black stork Ciconia nigra is listed as a focal species for guiding forest management in Estonia, where forestry has recently intensified and the stork population has suffered a twofold decline. We explored a possible link between the decline of the population and man-induced changes in forest structure, by analysing nesting of the species in relation to forest cover, edge effects and stand structure. Although the storks had distinct habitat preferences (old remote stands near rivers and a certain distance far from ecotones in well-forested landscapes), these were hardly reflected in site re-occupancy and productivity. Therefore, changes in forest structure are probably not responsible for the population decline, although preferences for specific forest environments may limit the range of potential nest sites. The results indicated that edge avoidance cannot be considered a species-specific feature over large areas and clear habitat preferences are not necessarily related with the present success of a population. We also suggest that lists of focal species should be regularly updated and validated in the field.