How much, why and where? Deadwood in forest ecosystems: The case of Poland

In forest management policy, deadwood is regarded as an indicator of sustainable forest management. Dead trees are a key habitat feature for a wide range of organisms. In this study, data from a regular network of nearly 30,000 sample plots (the National Forest Inventory) distributed throughout Poland were used to determine relationships between deadwood volume and thirteen selected natural and human-related factors: forest ownership, protection type, inclusion in the Natura 2000 network, terrain, slope gradient, site fertility, site moisture (water abundance), dominant species, age of the dominant species, stand volume, tree and shrub density, sapling and shrub cover, and stand damage. Analysis of data on deadwood volume was carried out in two steps: univariate analysis was used to determine present-day differences among forests, while a logistic regression model was applied to identify the factors that had the greatest impact on deadwood volume variability on the studied plots. Despite interference from numerous random effects that are difficult to capture and quantify, being often associated with disturbances and differences between the silvicultural approaches of individual forest managers, many of the analyzed factors were found to exert a significant influence. Strong relationships were identified mostly in managed forests (private, municipality-owned, and those managed by the State Forests National Forest Holding). In national parks and nature reserves, the identified effects were less pronounced due to the fact that the examined plots differed in terms of protection type and duration and may have been impacted by different natural disturbances. Indeed, deadwood volume was significantly affected by protection type, with much more deadwood found in strictly protected areas as compared to forests under active protection. Inclusion in Natura 2000 had only a slight effect. On the other hand, a major role was played by difficult terrain accessibility, which impeded silvicultural treatments. More deadwood occurred in the mountains, with increasing slope gradient positively affecting deadwood volume, but only up to a certain point. On the steepest slopes deadwood volume decreased due to the soil and wood sliding to a lower level. Deadwood volume was significantly greater on more fertile and moist sites. In managed forests, both stand age and growing stock volume were positively associated with deadwood accumulation. The species composition of stands, mostly attributable to habitat conditions, was also relevant. The present work identified some significant differences in deadwood volume between stands, and the findings may be useful in developing future management practices with a view to supporting biodiversity.