Making hollow trees: inoculating living trees with wood-decay fungi for the conservation of threatened taxa - a guide for conservationists

Decaying wood and cavities in living trees are fundamental determinants of forest biodiversity. However, a long history of forestry and land-use change has created a fragmented network of woodland with a depleted stock of veteran trees that support these microhabitats. Decomposition is a slow process and it may take heart-rot fungi hundreds of years to establish before hollowing even begins. A major challenge to forest restoration, therefore, is how these habitats can be restored or replicated. One approach is to inoculate trees with heart-rot fungi as a direct intervention to accelerate tree hollowing. We identify two types of conservation inoculation that could be beneficial in forest conservation: (1) Veteranising inoculations designed to benefit cavity and decay dependant fauna; and (2) Translocation inoculations, to reintroduce locally extinct, dispersal-limited heart-rot fungi. Tree inoculations have a hundred-year pedigree but successes have been mixed and there are no long-term published studies. Reflecting on previous heart-rot inoculations we discuss elements of the inoculation protocol to aid design of conservation inoculations. Conservation inoculations have the potential to be a useful tool in forest restoration and we hope to stimulate wider uptake as a direct method for conservation