The degradation and disappearance of natural ecosystems and habitats – including forests – is one of the most important factors behind the current global decline in biological diversity. Since most of terrestrial biodiversity is found in forests, restoration of these ecosystems or their natural characteristics has been proposed as one of the main strategies to counteract global species loss.
In this thesis, I examined the ecological effects of forest restoration in disturbance- driven boreal conditions. The applied restoration methods (prescribed burning; creation of canopy gaps; dead wood restoration) used natural forest disturbances as the reference point. Specifically, I focused on the effects that restoration has on tree species composition, age- class structure, and the amount and diversity of dead wood in forest ecosystems. In addition to examining the changes in these structural attributes, I investigated dead-wood-associated fungal communities in the restored substrates, and assessed whether dead wood restoration could be used to conserve rare and threatened fungal species.
Of the examined restoration treatments, the combination of prescribed burning and the creation of canopy gaps was found to be the most promising measure for the restoration of age-class structure and tree species composition in pine-dominated forests. Dead wood restoration – by artificially creating standing and fallen large-diameter dead trees – clearly enhanced the amount of dead wood in both pine and spruce dominated forests. Although dead wood restoration increased the abundance of fungal species in the examined forests, all aspects of the qualitative variation in dead wood was found to be difficult to restore in the short-term, since the restored dead wood was mainly in the initial stage of decomposition. The use of various restoration treatments (e.g. the creation of both standing and fallen dead wood) can compensate for some of the missing variation in fungal communities in the restored substrates.
Based on my results, disturbance-based restoration produces promising results by the rapid re-introduction of some of the most important structural attributes that have been lost from forests previously managed for timber production. Although the findings in this thesis show the clear positive effects that restoration has on the re-creation of naturally occurring forest characteristics, it appears difficult to restore all the inherent variability of natural forests. A particular challenge originates from the extended time scale of the natural processes, which have created and maintained the full array of ecological structures in forests, including the generally slow processes of stand succession and wood decomposition. To build a more comprehensive understanding of the potential of forest restoration for the conservation of endangered forest-associated species, a substantially longer monitoring period of restored forests would be useful in future studies.