Juha Siitonen

Biodiversity in Dead Wood

Preface 1. Introduction 2. Wood decomposition 3. The saproxylic food web 4. Other associations with dead woody material 5. Host tree associations 6. Mortality factors and decay succession 7. Microhabitats 8. Tree size 9. The surrounding environment 10. Evolution of saproxylic organisms 11. Species diversity of saproxylic organisms 12. Natural forest dynamics 13. Dead wood and sustainable forest management 14. Population dynamics and evolutionary strategies 15. Threatened saproxylic species 16. Dead wood in agricultural and urban habitats 17. The value and future of saproxylic diversity References Index.

Species richness of Coleoptera in mature managed and old-growth boreal forests in southern Finland

The beetle (Coleoptera) fauna of old-growth spruce (Picea abies) forest was compared with that from managed mature and overmature forests in southern Finland. Samples were collected from 9–11 sample plots in each case using 10 window-flight traps in each stand. These yielded a total of 43,289 beetles and 553 species of which 232 were associated with dead wood. The species richness of these saproxylic species was significantly higher in old-growth forests than in managed forests, and had very significant positive correlations with most dead-wood variables. Seventy eight percent of the saproxylic species were more abundant in old-growth than in mature managed forests, and their assemblages in managed and old-growth forests were distinctive with almost no overlap. On the other hand, species richness and assemblages of non-saproxylic species did not differ between the managed and old-growth forests. Obviously these species do not require as much attention as saproxylic species when conservation measures are planned in managed forests. An increase in the general level of decaying wood would improve the situation of many declining saproxylic species. Although the species richness of Coleoptera as a whole was higher in overmature than in mature managed stands, the value of long-rotation stands in preserving species assemblages typical of old-growth forests may be limited.

Occurrence of rare and threatened insects living on decaying Populus tremula: a comparison between Finnish and Russian Karelia

Beetles and flat bugs living on the decaying wood of aspen (mainly under bark) were collected during expeditions to Finnish and Russian Karelia. Similar searching methods were used, and a comparable number of sites and trees (about 120) were examined on both sides of the border. The fauna on aspen in Russian Karelia was considerably rich. A total of 21 and 5 rare species were found in Russian Karelia and Finnish Karelia, respectively. Within about twenty working hours in Russ. Karelia we encountered two species considered extinct in Finland (Hylochares cruentatus and Cyllodes ater) and five considered endangered or vulnerable (Acritus minutus, Rhacopus attenuatus, Uleiota planata, Cucujus cinnuberinus and Anidus truncatus). We suggest that the high number of rare species at the sites studied in Russian Karelia is attributable to the different management history of the forests, particularly to the abundance and continuity of large, dead aspens. Disturbance caused by logging and leaving the non‐marketable t...

Amount and quality of coarse woody debris in natural and managed coniferous forests near the timberline in Finnish Lapland

Amount and structural characteristics of coarse woody debris (CWD) were studied in 44 stands of old‐growth and managed coniferous forests in Finnish Lapland. The average volume of CWD in old‐growth forests varied from 19 m3 ha−1 in pine forests to 60 m3 ha−1 in herb‐rich spruce‐dominated forests. The volumes of living and dead timber were highly correlated, the most productive sites having the highest volumes. In old‐growth forests about 60–70% of the CWD was logs, 30–40% standing dead trees and snags, and 3.5–7% stumps and branches. The amount of CWD decreased considerably in clear‐cutting, but increased or remained the same in seed‐tree and selective cuttings in the short term. However, the accumulation rate of new dead material was greatly reduced after cutting. In 40‐year‐old seed‐tree cutting areas the new supply of CWD, created by recent disturbance and mortality, was less than 1% of the respective amount in old‐growth forest. All cutting methods reduced standing dead trees and snags considerably.

Modeling species co‐occurrence by multivariate logistic regression generates new hypotheses on fungal interactions

Signals of species interactions can be inferred from survey data by asking if some species occur more or less often together than what would be expected by random, or more generally, if any structural aspect of the community deviates from that expected from a set of independent species. However, a positive (or negative) association between two species does not necessarily signify a direct or indirect interaction, as it can result simply from the species having similar (or dissimilar) habitat requirements. We show how these two factors can be separated by multivariate logistic regression, with the regression part accounting for species-specific habitat requirements, and a correlation matrix for the positive or negative residual associations. We parameterize the model using Bayesian inference with data on 22 species of wood-decaying fungi acquired in 14 dissimilar forest sites. Our analyses reveal that some of the species commonly found to occur together in the same logs are likely to do so merely by similar habitat requirements, whereas other species combinations are systematically either over- or underrepresented also or only after accounting for the habitat requirements. We use our results to derive hypotheses on species interactions that can be tested in future experimental work.

Predicting the decomposition of Scots pine, Norway spruce, and birch stems in Finland.

Models were developed for predicting the decomposition of dead wood for the main tree species in Finland, based on data collected from long-term thinning experiments in southern and central Finland. The decomposition rates were strongly related to the number of years after tree death. In contrast to previous studies, which have used the first-order exponential model, we found that the decomposition rate was not constant. Therefore, the Gompertz and Chapman-Richards functions were fitted to the data. The slow initial decomposition period was mainly due to the fact that most dead trees remained standing as snags after their death. The initial period was followed by a period of rapid decomposition and, finally, by a period of moderately slow decomposition. Birch stems decomposed more rapidly than Scots pine and Norway spruce stems. Decomposition rates of Norway spruce stems were somewhat lower than those of Scots pine. Because the carbon concentration of decaying boles was relatively stable (about 50%) the rate of carbon loss follows that of mass loss. Models were also developed for the probability that a dead tree remains standing as a snag. During the first years after death, the probability was high. Thereafter, it decreased rapidly, the decrease being faster for birch stems than for Scots pine and Norway spruce stems. Almost all stems had fallen down within 40 years after their death. In Scots pine and Norway spruce, most snags remained hard and belonged to decay class 1. In birch, a higher proportion of snags belonged to the more advanced decay classes. The models provide a framework for predicting dead wood dynamics in managed as well as dense unthinned stands. The models can be incorporated into forest management planning systems, thereby facilitating estimates of carbon dynamics.

Habitat requirements and conservation of Pytho kolwensis, a beetle species of old-growth boreal forest

Abstract The host-tree and habitat requirements of an endangered saproxylic beetle species, Pytho kolwensis , which inhabits fallen spruce ( Picea abies ) trunks were studied. Host-tree quality of 150 potential host trees, 60 of which were inhabited, and stand characteristics were measured at six sites in eastern Finland. All of the P. kolwensis habitats were virgin spruce-mire forests with a stand continuity of at least 170–300 years, and a high volume of dead wood (73–111 m 3 /ha). Decay-class distribution of large-diameter logs was very even, indicating that the recruitment rate of large, fallen trunks had remained nearly constant for at least 100 years. Microclimate and host-tree quality were not likely factors explaining the habitat confinement of the species. We suggest that P. kolwensis is mainly restricted to spruce-mire forests because of the long-term continuous availability of suitable host trees in these habitats.

Woodland key habitats in northern Europe: concepts, inventory and protection.

Abstract The woodland key habitat (WKH) concept has become an essential instrument in biodiversity-orientated forest management in northern Europe. The philosophy behind the concept is basically the same in all of the countries: to conserve the biodiversity of production landscapes by preserving small habitat patches that are supposed to be particularly valuable. This article reviews the definitions, inventories and implementation processes of WKHs in Sweden, Finland, Norway, Latvia, Estonia and Lithuania. Sweden and the Baltic countries have similar WKH models, while the models in Finland and Norway are clearly deviating. Depending on the country, the definitions emphasize different factors, such as soil and bedrock properties, stand structure and occurrence of indicator species. The mean size of the WKHs varies considerably, from 0.7 ha (Finland) to 4.6 ha (Sweden). The degree of formal protection also differs. Preservation of WKHs is primarily based on forest legislation in Finland, Estonia and Latvia, and on forest certification in the other countries. The implementation of the WKH concept is inconsistent between the countries, resulting in different sets of habitats being included in the WKH networks. This makes direct comparisons between the countries difficult, and may hamper the generalization of research results into other areas.

Significance of woodland key habitats for polypore diversity and red-listed species in boreal forests

Preservation of woodland key habitats has become an integral part of biodiversity-oriented forest management in northern Europe. In Finland, brook-side spruce forests constitute the most important key-habitat type in terms of total area and timber volume. Our aim was to compare polypore diversity and the occurrence of red-listed species between brook-side key habitats and comparable sites of managed forest as controls. Furthermore, we assessed the importance of stand structural features to polypore communities, and contrasted regions with different land-use history. Altogether 69 key habitats and 70 controls were inventoried in four regions across southern Finland. A total of 28,023 surveyed dead-wood units had 3,307 occurrences of 114 species of which 25 species were red-listed. Key habitats hosted on average 28% (about two species) more polypore species (mainly deciduous-specialists) than controls because of a larger average volume of dead wood and a higher proportion of dead deciduous wood. However, the average number of red-listed species was low and did not differ between the two forest categories. We detected a landscape effect connected with the intensity and length of forest management history, with the highest numbers of all and red-listed species per site in eastern Finland. Volume and diversity of dead wood were the most important variables explaining variation in species richness. Presently, key habitats in managed forests appear to contribute only little to the conservation of red-listed polypore species.

Evaluating citizen science data for forecasting species responses to national forest management

Abstract The extensive spatial and temporal coverage of many citizen science datasets (CSD) makes them appealing for use in species distribution modeling and forecasting. However, a frequent limitation is the inability to validate results. Here, we aim to assess the reliability of CSD for forecasting species occurrence in response to national forest management projections (representing 160,366 km2) by comparison against forecasts from a model based on systematically collected colonization–extinction data. We fitted species distribution models using citizen science observations of an old‐forest indicator fungus Phellinus ferrugineofuscus. We applied five modeling approaches (generalized linear model, Poisson process model, Bayesian occupancy model, and two MaxEnt models). Models were used to forecast changes in occurrence in response to national forest management for 2020‐2110. Forecasts of species occurrence from models based on CSD were congruent with forecasts made using the colonization–extinction model based on systematically collected data, although different modeling methods indicated different levels of change. All models projected increased occurrence in set‐aside forest from 2020 to 2110: the projected increase varied between 125% and 195% among models based on CSD, in comparison with an increase of 129% according to the colonization–extinction model. All but one model based on CSD projected a decline in production forest, which varied between 11% and 49%, compared to a decline of 41% using the colonization–extinction model. All models thus highlighted the importance of protected old forest for P. ferrugineofuscus persistence. We conclude that models based on CSD can reproduce forecasts from models based on systematically collected colonization–extinction data and so lead to the same forest management conclusions. Our results show that the use of a suite of models allows CSD to be reliably applied to land management and conservation decision making, demonstrating that widely available CSD can be a valuable forecasting resource.