Low-level retention forestry, certification, and biodiversity: case Finland

In managed forests, leaving retention trees during final harvesting has globally become a common approach to reconciling the often conflicting goals of timber production and safeguarding biodiversity and delivery of several ecosystem services. In Finland, the dominant certification scheme requires leaving low levels of retention that can benefit some specific species. However, species responses are dependent on the level of retention and the current low amounts of retention clearly do not provide the habitat quality and continuity needed for declining and red-listed forest species which are dependent on old living trees and coarse woody debris. Several factors contribute to this situation. First, the ecological benefits of the current low retention levels are further diminished by monotonous standwise use of retention, resulting in low variability of retention habitat at the landscape scale. Second, the prevailing timber-oriented management thinking may regard retention trees as an external cost to be minimized, rather than as part of an integrated approach to managing the ecosystem for specific goals. Third, the main obstacles of development may still be institutional and policy-related. The development of retention practices in Finland indicates that the aim has not been to use ecological understanding to attain specific ecological sustainability goals, but rather to define the lowest level of retention that still allows access to the market. We conclude that prevailing retention practices in Finland currently lack ecological credibility in safeguarding biodiversity and they should urgently be developed based on current scientific knowledge to meet ecological sustainability goals.

The Potential of Production Forests for Sustaining Lichen Diversity: A Perspective on Sustainable Forest Management

There is a critical gap in our knowledge about sustainable forest management in order to maintain biodiversity with respect to allocating conservation efforts between production forests and set-asides. Field studies on this question are notably scarce on species-rich, poorly detectable taxon groups. On the basis of forest lichen surveys in Estonia, we assessed the following: (i) how much production stands contribute to maintaining the full species pool and (ii) how forest habitat conditions affect this contribution for habitat specialist species. The field material was collected in a “semi-natural forestry” system, which mitigates negative environmental impacts of even-aged forestry and forestry drainage by frequently using natural regeneration, tree retention, and low intensity of thinnings. We performed standard-effort surveys of full assemblages of lichens and allied fungi (such as non-lichenized calicioid and lichenicolous fungi) and measured stand structure in 127 2 ha plots, in mainland Estonia. The plots represented four management stages (old growth, mature preharvest forests, clear-cut sites with retention trees, and clear-cut sites without retention trees). The 369 recorded species represent an estimated 70% of the full species pool studied. Our main finding was that production forests supported over 80% of recorded species, but only one-third appears tolerant of management intensification. The landscape-scale potential of production forests through biodiversity-friendly silviculture is approximately twice as high as the number of tolerant species and, additionally, many very rare species depend on setting aside their scattered localities. The potential is much smaller at the scale of individual stands. The scale effect emerges because multiple stands contribute different sets of sensitive and infrequent species. When the full potential of production forests is realized, the role of reserves is to protect specific old-growth dependent taxa (15% to 20% of the species pool). Our study highlights that production forests form a heterogeneous and dynamic target for addressing the biodiversity conservation principle of sustainable forest management.

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

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.

Towards silvicultural mitigation of the European ash (Fraxinus excelsior) dieback: the importance of acclimated trees in retention forestry

The European ash (Fraxinus excelsior L.) dieback is an acute forest pathology problem caused by the invasive ascomycete Hymenoscyphus fraxineus (T. Kowalski) Baral, Queloz, Hosoya. There are no practical solutions yet, but selection for resistant genotypes and intensive care have been highlighted as options. Our aim was to assess the disease mitigation potential of silvicultural harvests, which influence stress levels in retained trees. We annually monitored 577 retention trees on Estonian cut areas for 13 years, including 9 years impacted by the dieback. Sixty-five percent of the trees survived and 15% retained healthy crown, despite all sampled trees being infected. The damage was smallest in the trees retained near precut edges. Former forest-interior trees that were left in central parts of the cut areas suffered high initial damage but smaller disease progression than trees near postcut edges. Tree size and secondary infection by Armillaria spp. were not related to disease progression, but rapid decline was observed in the region with the highest density of ash trees retained. Our results indicate a significant silvicultural potential for tree resistance. Ash trees tend to be healthiest in open conditions, which probably inhibit the pathogen and provide better resources for the tree. Location near precut edges is an important tree retention criterion, which can mitigate initial harvest-induced stress.