Oak harvesting benefits lichen and moss

A recent research project by Norden and colleagues investigated the effect of oak forest thinning on epiphyte populations in Sweden. Selective oak harvesting in these areas is undertaken to meet demand for biofuel.

Small and intermediate sized trees were harvested in 24 forests with monitoring of both lichen and moss populations. Forest plots were surveyed before and six years after the removal of about 25% of the tree basal area. 

Oak forest. Photo: C. Kirby.

The researchers found that the areas with partial harvesting had greater rate of host tree colonisation by lichens and mosses. This is possibly due to higher light levels but there was not enough evidence to support this idea. 

The increase in lichen density was greatest on oaks with small diameters and deep bark crevices. The researchers conclude that "A mild form of biofuel harvesting may represent sustainable resource-use in these forests, compatible with conservation. However, part of the forest should be kept untouched for species vulnerable to changes in microclimatic conditions and for evaluation of long-term effects."

Lichen on an oak tree. Photo: M. Vorderbruggen.

This is a very interesting piece of work, especially with the focus on such a different ecosystem. The greater diversity of epiphytic species in New Zealand means that the lessons don't directly apply for us but it highlights the different requirements of different epiphytic life forms.