The multidisciplinary research program Smart Tree Retention (2009 – 2016; funded by the Swedish research council Formas) reports results from projects on ecology, economy, forest planning, environmental history and human perception. For biodiversity, overall positive effect have been found compared to traditional clearcutting. New perspectives are also given on land-use in the past land as well as in the future, and on the implementation of this practice, relating to forest certification.
In Sweden and in many other parts of the world, clearcutting has been modified to create better conditions for biodiversity and to maintain various ecosystem services. Trees and tree groups are left at harvest often in special habitats like along lakes and watercourses and dead wood is saved and also created. In Sweden such actions are to be taken at every logging occasion, according to the law and such recommendations are also a key part of certification standards. Eight percent of the stand area is retained at final felling, as an average for the country. Retention forestry complements other types of conservation like voluntary set-asides and nature reserves.
Smart Tree Retention has initiated several syntheses of research in collaboration with international colleagues. One synthesis describes where and how retention forestry is practiced in different parts of the world and shows that this model is most common in north Europe and North America but that it is also practiced in parts of Australia and South America (1, 2).
In a meta-analys where data from many studies were analysed jointly a main result was that logged areas with retention have more species compared with traditional clearcuts and also with older forest. But, for some species retention is not enough and instead larger areas need to be protected (3, 4).
In one review, ecological studies on retention made in Sweden, Finland and Norway are summarized. A main conclusion is that much of the research in this region has been directed towards insects while other species groups, like birds, are much less studied (5). In an overview of forest biodiversity conservation in Sweden, researchers discuss pros and cons with current practices (6).
Two PhD-projects have increased the understanding of drivers of species richness, survival and habitat choice among beetles, bees and other aculeates. Both theses show that harvested areas can be important for rare species, especially when dead trees are retained (1, 2, 4).
In one thesis, landscape properties surrounding logged areas were at least as important as the environment in the stand itself (3). The other thesis shows that standing dead trees can be important nesting sites for aculeates but also that the abundance of flowering plants along roadsides close to the logged stand can be significant for certain bees (4, 5).
Retention forestry, as opposed to clearcutting, is a prerequisite for future supply of large trees and old stands in production forest landscapes. This was revealed in a simulation study of future forest landscapes (200 years) under different scenarios regarding proportion retention (1). The amount of retained trees is fundamental to the outcome; for example 20% retention will result in four times more dead wood compared to no retention. Visualizations of future forest landscapes and stands show that retention actions are important for the visual impression of future forests. Another study, using data from Swedish National Forest Inventory, shows that the amount of dead and old trees has increased in Sweden during the last decades, as a result of the application of retention forestry (2).
A study from middle Sweden shows that tree groups on harvested areas (retention patches) at least 0.1 ha large have higher abundance of common species like the dwarf shrub billberry Vaccinium myrtillus and the moss Hylocomium splendens than open, clearcut areas.
Edge effects are large though and uncommon species, like the orchid Goodyera repens, will have difficulties to survive (1). In a study before and after harvest, survival of red-listed bryophytes on dead wood was 50% in retention patches compared with only 10% on open, clearcut areas (2).
A study from a retention experiment in pine-dominated forest in Finland reveals that even 17% retention is not enough to affect the composition of ground vegetation (3). Retained aspens after harvest may host a rich lichen flora including several rare species and number of species increases with time (4). The northern sides of retained aspens are especially important to some logging-sensitive bryophytes and lichens since they provide comparatively dark and humid conditions (5)
Good communication within the organisation is important for the implementation of certification. On the picture Börje Pettersson and Per Skoog, Stora Enso. Photo: Lena Gustafsson
Implementation of retention actions prescribed in certification is in large a matter of communication within the forest organization. Good performance depends on “logistics of information” between different links in the planning and management chain, from the highest organization management to the machine operator. There are different ways to improve ground performance of certification, for instance increased integration with environmental management systems, larger patency in responsibilities and by establishing more clear requirements in the forest planning. To create a learning culture and internal audits are other suggestions for improvement (1).
Johansson, J., & Keskitalo, E. C. H. (2014). Coordinating and implementing multiple systems for forest management: implications of the regulatory framework for sustainable forestry in Sweden. Journal of Natural Resources Policy Research, 6(2-3), 117-133. .
Criticism towards industrial forestry grew strong in the beginning of the 1970s, especially towards chemical control of deciduous tree regeneration but also towards the clearcutting practice. Shortly after, researchers began reporting decrease in populations of certain plant and animal species and suggested different ways to integrate environmental consideration within forestry operations. As a consequence of this the perhaps most important driving force developed, the compilation of Red Lists of threatened species, in the mid 1980s. About a decade later international customers of Swedish forest products demanded increased environmental concern within Swedish forestry. This contributed to the adoption of international certification programs in the country around the turn of the millennium, and in these retention actions were an important component (1).
A study in middle Sweden shows that a deliberate selection of aspen trees with small diameter, special stem architecture and structure of the bark would lead to fewer trees having to be retained compared to a random selection (1). Lichens were used as study species. The saving achieved could be used to retain more aspen trees, and thus further increase the value to biodiversity. It is difficult to draw firm conclusions based on this study since it is the first of its kind. More studies on other tree species and using other study organisms are needed to make more general recommendations.
Perhans, K., Haight, R., Gustafsson, L. 2014. The value of information in conservation planning: Selecting retention trees for lichen conservation. Forest Ecology and Management 318: 175–182
One way to understand how people perceive harvested areas is to measure their eye movements, a method being increasingly used in research. In such studies it is important to use high-quality and homogenous images, either photographs or visualizations (1). Experts (ecologists) and non-experts value harvested areas with retention similarly but they move their eyes in different ways. Experts focus more on the vegetation on the ground when they estimate biodiversity and they also search images more intensively compared to non-experts (2).
Pihel, J., SANG, Å. O., Hägerhäll, C., Nyström, M., & Sandström, E. 2014. Assessments and Eye Movements Compared between Photographs and Visualizations of Logged Forest Vistas–For What Kind of Assessments are Visualisations a Good Representation of Photographs?. In Digital Landscape Architecture DLA 2014 (pp. 344-351). Berlin: Wichmann Verlag.
Pihel, J., Sang, Å. O., Hagerhall, C., & Nyström, M. 2015. Expert and novice group differences in eye movements when assessing biodiversity of harvested forests. Forest Policy and Economics 56: 20-26.
Lena Gustafsson, professor
Department of Ecology, SLU
lena.gustafsson@slu.se 018-672747, 070-3022747