Modelling dead wood in Norway spruce stands subject to different management regimes
ABSTRACT Strategies for preserving biodiversity in boreal forests should include the maintenance of coarse woody debris (CWD) because this substrate is a key feature for the preservation of many threatened species. Computer simulation programs are useful tools for predicting the amount of CWD that will arise if certain management practices are applied in the long term. We have constructed and used a simulation program based on stochastic equations, which aims at predicting the amount of CWD in homogenous stands of Norway spruce in central Scandinavia. Because the rate of tree mortality is a critical factor in such simulations, we present such data derived from spruce-dominated forests surveyed in the Swedish National Forest Inventory.A comparison between simulation outcomes and field data shows that the average quantity of CWD in today’s managed forest is possible to predict using the simulation model. If the forest is managed according to the Forest Certification Standard, the amount of CWD (diameter larger than 10 cm) will be almost three times higher as the amount in today’s managed forests. The amount of CWD was found to be highest in old stands and immediately after cutting. In stands of an intermediate age the amount of CWD was low, especially CWD in early decay stages and of larger sizes. High productivity and long rotation time tended, on average, to increase the amount of CWD in stands. Among the management practices recommended in the new biodiversity-oriented forestry, retention of small areas with living trees is the most efficient way to increase the average amount and continuous occurrence of CWD within a stand, at least if the retained areas are as productive as the main part of the stands.
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ABSTRACT: To evaluate which qualities of dead wood have the highest conservational value for invertebrates, substrate requirements were recorded for all 542 saproxylic (wood-living) red-listed invertebrates in Sweden. Preferred qualities of dead trees were described for each species in seven category variables: tree species, stage of decay, type of main stem, coarseness of stem, part of tree, light preference and microhabitat. For each quality we quantified the number of red-listed insect species using it and the number that are specific to the quality. The number of species associated with different tree genera ranged from five to 202. Species-rich genera had a higher proportion of monophagous species. To what extent different tree genera have faunas complementary to each other was also analysed. As the wood decays, the host range broadens and the flora of decay fungi will probably take over as the most important factor determining the saproxylic fauna. Because there are many different types of rot required by different invertebrates, an abundance of similar looking dead trees, logs and snags are probably needed. Some 59% of the invertebrate species can live in sun-exposed sites. Most of these are favoured when the forest burns and at least 29 of them are more strongly associated with fires. For the former category, leaving dead wood on clear cuts should be an effective way to increase the amount of breeding substrate. However, some species, especially those living in the last successional stages, are dependent on shaded sites. Hollow tree trunks are another important microhabitat; 64 of the 107 species living there are specialists. To maintain all saproxylic species we need a diversity of substrate types and management methods. Our data can help to decide how to optimize the conservation measures taken during forest operations.Biodiversity and Conservation 05/1998; 7(6):749-764. · 2.26 Impact Factor
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ABSTRACT: Stand structure was studied on thirty 1-ha plots in mature managed and old-growth forest stands dominated by Norway spruce (Picea abies L. Karst.) in southern Finland. The forests were classified into three categories (10 plots in each category) according to the age of the dominant spruces and signs of previous cutting: (1) mature managed (95–118 years), (2) overmature managed (124–145 years) and (3) old-growth (129–198 years).The average volume of the living trees was 299 m3/ha in mature, 331 m3/ha in overmature and 396 m3/ha in old-growth stands. The clearest difference in the living stand characteristics between the categories was in the numbers of large pines (Pinus sylvestris L.) and deciduous trees, which were both ca. 10 times more frequent in old-growth than in mature stands, and intermediate in overmature stands. The average volume of coarse woody debris (CWD) with a minimum diameter of 5 cm was 14 m3/ha in mature (range 2–28 m3/ha), 22 m3/ha in overmature (7–38 m3/ha) and 111 m3/ha (70–184 m3/ha) in old-growth stands. Stand age and basal area of the cut stumps together explained over 70% of the variation in the volume of CWD. In old-growth forests, ca. 70% of the volume of CWD consisted of logs, 23% of intact dead standing trees and 7% of broken snags. Most of the volume of CWD belonged to the 20–29 and 30–39 cm diameter classes, but the mean proportion of large trunks ≥40 cm was also considerable, 24%. In managed forests man-made CWD, consisting of cut stumps, bolts and logging residues, accounted for an average of 25% of the total volume of CWD. In many cases most of the CWD volume belonged to the small diameter classes, 5–9 and 10–19 cm, and the mean proportion of large trunks was only 8%.We suggest that, considering the low proportion of both old-growth and overmature forests in southern Finland and the long time required for old-growth characteristics to develop, the most efficient short-term management strategy to increase structural diversity and old-growth attributes in managed forests would be to apply harvesting methods retaining the old-growth characteristics (i.e. large living trees, snags and logs) that already exist in overmature and mature stands.Forest Ecology and Management. 01/2000;
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ABSTRACT: Five circular forest fragments of increasing size (, , , ) were isolated in 41-ha clearcut in north-western Sweden. I compared changes in the forest structure of these fragments with those of three control plots in adjacent unfragmented forest, during a five-year period. The site was a high-altitude, old-growth Picea abies forest.In the first autumn after isolation a period with high winds caused severe blowdown and other forest damage in all five fragments. Total tree mortality after 67 months showed a steep increase with decreasing area, from 30% in the 1-ha fragment to 98% in the fragment. Uprooting was the most common type of mortality (67%) followed by stem-breakage (24%). The marked increase in wind-induced tree deaths shifted the mortality pattern, from being independent of tree size in controls to showing a strong positive relationship with diameter in fragments.The study shows that completely isolated forest fragments up to at least 1 ha in size became entirely edge habitat shortly after logging. Edge-related changes in forest structure, deposition of woody debris and soil disturbance, triggered by altered climate, are key factors for understanding ecological processes operating in forest fragments. This supports the view that changes in small fragments are mainly driven by external factors.Biological Conservation. 01/1994;