Cost-efficiency of measures to increase the amount of coarse woody debris in managed Norway spruce forests
Introduction
Modern forestry changes and destroys the habitat for many forest-living organisms. To preserve biodiversity, forests are set aside as reserves, however, especially during the last decade this approach has been combined with changes of the silvicultural methods, which aim at increasing the habitat quality for forest species in managed forests (e.g. Larsson and Danell, 2001, Putz et al., 2001). Forest certification has accelerated this development, at least in temperate areas, as it makes it possible for consumers to identify products from sustainable forestry, which potentially gives a greater market access and higher prices for products from sustainable forestry (Gullison, 2003). Sweden and Finland are examples of countries where the current strategy for biodiversity preservation to a large extent is based on improvements of forest habitats by changed silvicultural methods (Raivio et al., 2001).
Coarse woody debris (CWD) is a key feature for preservation of threatened organisms in boreal forests (e.g. Berg et al., 1994, Harmon et al., 1986, Jonsell et al., 1998, Siitonen, 2001). This is because a large proportion of the species in boreal forests are saproxylic (Hanski and Hammond, 1995, Siitonen, 2001), i.e. they depend directly on dead wood or on other saproxylic species during some part of their life cycle (Speight, 1989). Forest management in Fennoscandia has decreased the volume of coarse woody debris (CWD) to 2–30% (usually <10%) of the quantity found in old-growth boreal forests (Fridman and Walheim, 2000, Siitonen, 2001). Many saproxylic organisms suffer from the decrease in habitat due to modern forestry (Kouki et al., 2001). Some species occur mainly in the core of unmanaged forest areas (Moen and Jonsson, 2003, Berglund and Jonsson, 2003), and they may be impossible to preserve by changing the silviculture practice on managed forestland. However, there are also many red-listed species that colonise logs and artificially created high stumps both in closed forest and on clear-cuts (Lindhe, 2004). Therefore, a change of management may be an efficient complement to old-growth protection, especially for the preservation of species associated with young successional stages (Kouki et al., 2001).
The importance of CWD for biodiversity preservation is acknowledged by the Swedish government; according to Swedish governmental goals, the quantity of CWD should increase (Anonymous, 2001). Changes in the silvicultural practices brought about by adaptations to the FSC standard (Anonymous, 2000), will, at least in the long run, make it possible to considerably increase the amount of CWD (Ranius and Kindvall, 2004). To maintain CWD, trees (dead or alive) must be left in the forests. Because the wood in the trees constitutes the economically most important resource in the forest, there is an obvious potential conflict between increasing the amount of CWD and the economics of silviculture. Therefore, it is important that environmental considerations are performed in a cost-efficient manner. A cost-efficient environmental practice means that a given cost spent on the environment improves the environmental quality as much as possible, or that the cost for a given level of environmental quality is as low as possible (Baumol and Oates, 1988). Carlén et al. (1999) estimated effects on biodiversity at final logging by ranking consideration measures according to how they believed that animals were affected. They found that many measures entailed no negative effect, or even a positive effect, on the net revenue of final logging, indicating potentially large unexploited improvements in cost-efficiency.
To analyse the cost-efficiency of different management strategies, which allow long-term persistence of the fauna and flora dependent on CWD, empirical data as well as models of economics, dead wood dynamics and population dynamics of species associated with CWD are required. One previous attempt has considered costs and tree mortality (Wikström and Eriksson, 2000), while a case study on a saproxylic liverwort has demonstrated that it is possible to also include dead wood dynamics and assumptions regarding saproxylic organisms’ population dynamics (Kruys and Wikström, 2001). In this study, we use information available for Norway spruce (Picea abies L. Karst.) forests in Sweden. Norway spruce and Scots pine (Pinus sylvestris L.) are the dominant tree species in Fennoscandia. About 1200 species are associated with dead Norway spruce trees in Sweden, of which more than 300 are red-listed (Dahlberg and Stokland, 2004). However, most saproxylic species may be found on more than one tree species; only 30 species are regarded as specialists on Norway spruce (Dahlberg and Stokland, 2004). We predict the opportunity cost and amount of CWD in stands subject to different management regimes. The opportunity cost of an action to increase CWD is the difference between the maximum present value that can be obtained from the stand, and the present value obtained with a management regime adopted to increase the amount of CWD. We compared five different management measures (retention of living trees at harvest, artificial creation of high stumps, manual scarification at clear-cuts to avoid destruction of CWD, prolongation of the rotation period, and retention of naturally dying trees) that may be performed to preserve biodiversity associated with CWD. We estimated how much CWD are generated and what the economic consequences are for a landowner when different measures are taken to increase CWD. We compared forest stands in three different parts of Sweden, to analyse whether the same measures are the most cost-efficient everywhere. If there are differences, it suggests that there should not be one single management recommended for all Norway spruce forests in Sweden, but that recommendations should be differentiated regionally.
Section snippets
Methods
For each of the management scenarios analysed, two kinds of data were obtained as output: monetary cost and amount of CWD. We used three models, one that deals with the development of the forest stand, one that deals with the economic outcome (Ekvall, 2001), and one that deals with CWD (Ranius et al., 2003).
Management regime and volume of CWD
The rotation period that maximized present value was between 70 and 130 years, with a shorter period for more productive stands (Table 7). When the present value was maximized, the predicted amount of CWD was highest in the south (Kronoberg), and lowest in the north (Västerbotten, Table 8). Different discount rates generate different management regimes (Table 7). With a lower discount rate, more CWD was generated (Table 8).
A comparison between measures prescribed by the FSC-standards in Sweden
Cost-efficiency
The cost-efficiency of measures to increase CWD differed somewhat between geographic regions, whereas varying the discount rate only had minor effects on cost-efficiency (Table 8, Table 9 and Fig. 1, Fig. 2). In all regions, creating high stumps was cost-efficient. Important reasons for this are that all wood that is not harvested due to this management measure becomes CWD and almost no area has to be excluded from production. In the northernmost county Västerbotten, manual scarification was
Acknowledgements
Mattias Boman, Barbara Ekbom, Göran Ericsson, Peichen Gong, Oskar Kindvall, Stig Larsson, Martin Schroeder, Erik Sollander and Peder Wikström have provided valuable comments on this manuscript. Support for this project came from the project ‘Cost-efficiency of a biodiversity-oriented forestry’ financed by The Swedish Research Council for Environment, Agricultural Sciences and Spatial Planning (FORMAS), by the Oscar and Lili Lamm Memorial Foundation, from the project ‘Conservation of
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