Forests generate many types of deadwood: standing dead trees and trunks lying on the ground, deciduous or coniferous trees. Fresh decaying wood can be thin and sturdy, or present as trunks that have already rotted and are covered by moss. A diverse selection of deadwood translates into a diverse selection of habitats suitable for many species that thrive in forests.
Deadwood is a key element of the forest ecosystem. Roughly a quarter (4,000 to 5,000) of Finland’s forest species depend on deadwood at some stage of their lifecycle. This number is even higher for endangered species, a third of whom are endangered because of the decreasing quantity of deadwood in forests. Deadwood is the most significant structural feature impacting the biodiversity of Finnish forests, and its existence is a basic requirement for a healthy forest ecosystem.
Many species living on decaying wood are specialised for a certain type of tree and a certain size of deadwood, and sometimes even for a certain degree of wood decay. In time, as the wood decay progresses, species need to find a new habitat consisting of a suitable type of tree and degree of decay. It is therefore important to ensure that decaying wood of a range of ages and tree types is available throughout the forest cycle.
Forest hygiene guidelines prevalent a few decades ago advised clearing all deadwood from forests. However, methods have since evolved and current forest management recommendations and forest certification requirements advise that deadwood be left in situ.
National forest inventory data from last twenty years shows an increase in the quantity of sturdy deadwood in commercial forests, confirming that the practical impact of the new guideline is already quantifiable. The most recent species conservation status evaluations offer indications on how the actual aim of deadwood preservation – promotion of the diversity of species that depend on deadwood – is realised. They show that it has been possible to downgrade the conservation status of many such species to a lower category. Nature management measures, such as retention trees and deadwood preservation, have been identified as some of the reasons behind this positive outcome.
Leaving deadwood in forests is probably the simplest and most economical environmental management measure, as it does not require any specific interventions and deadwood as such is not financially valuable raw material. However, deadwood preservation can generate remarkable biodiversity benefits, making it an extremely cost-effective way of promoting environmental values in commercial forests.
There is also no financial benefit in clearing out individual deadwood trunks. Deadwood has no use in industrial wood processing and it is not worth the while to collect decayed trunks for energy production because of their poor capability to generate energy. Tree collection costs tend to exceed the profit that such trees generate easily. Therefore, investing in the collection of deadwood trunks is not financially feasible for forest owner.
When natural disturbances, such as storms, result in large quantities of fresh deadwood or damaged wood material, forest owners should plan their actions with the health of the forest in mind, to prevent further damage. Legislation on the prevention of forest damage specifies that when the quantity of damaged coniferous trees exceeds defined limits, they must be cleared from the forest to prevent the spread of insect and fungi damage.
Forest Damage Prevention Act requirements only apply to fresh trees with bark. However, deadwood that has been in the forest over a winter season no longer poses a risk and thus does not need to be cleared away to prevent forest damage.
In forestry based on multiple objectives, deadwood is most valuable left exactly where the nature leaves the trunks. Forest owners may also appreciate the financial benefit resulting from deadwood preservation because a diverse and well-functioning forest ecosystem is the best guarantee of the forests’ productivity in the long term.
Tips for deadwood preservation
- Leave sturdy fallen deadwood trunks intact in their original location. If necessary, trunks can be moved aside if they block haul roads, for instance.
- Do not clear out standing deadwood trunks. If a tree causes a safety risk because it is located near roads or power lines, fell the tree and leave it in place as a fallen deadwood trunk.
- Due to their scarcity in Finland’s primarily coniferous forests, deciduous deadwood trunks are particularly valuable for biodiversity.
- Leave some stumps and logging residue on the ground when felling trees intended for energy production.
- Any living retention trees left on felling sites today will become tomorrow’s deadwood trunks, ensuring the continuing availability of deadwood in the long term.
- Some groups of species benefiting from deadwood preservation are beetles and the fungi species aphyllophorales, for instance.