Declining number of oaks and secondary woodland reduces the diversity of red-listed lichens on ancient oaks

Chaenotheca Phaeocephala -

 a lichen growing on ancient oaks

Wooded pastures with ancient oaks were formerly abundant throughout Europe. The oaks have been cut to a large extent, and in the remaining wooded pastures grazing has largely been abandoned, often resulting in dense forests. Ancient oaks constitute habitat for a diversity of lichens, bryophytes, fungi, beetles, pseudoscorpions, moths, birds, bats, and many of these species are now declining and threatened. 

An open standing ancient oak              

Our research group, based in southern Sweden, has quantified the effects of the declining number of oaks and the effect of secondary woodland on epiphytic lichens: nationally and regionally red-listed lichens that strongly prefer old oaks as substrate. We found that the number of these lichens in secondary woodland was about half of the number of the lichens in open conditions. We also tested if the species number and occurrences of individual species were affected by the density of large oaks in the surrounding landscape. The occurrence of five lichen species (Cliostomum corrugatum, Buellia violaceofusca, Calicium adspersum, Ramalina baltica, Chaenotheca phaeocephala) increased with increasing density of ancient oaks in the surrounding landscape (within a radius of 500-5000 meters from the study oaks). 

An ancient oak shaded by a spruce

Our research suggests that threatened lichens on ancient oaks are dependent on open conditions and that restoration is therefore desirable in secondary woodlands with ancient oaks. In addition, conservation of ancient oaks and restoration would be more efficient, in terms of a higher number of red-listed lichens, in landscape areas with dense occurrences of ancient oaks, or in landscape areas in which the aim is to increase the number of oaks in future. The most important restoration actions include clearing the young trees from around the oaks, and planting new oaks.

Heidi Paltto, PhD, Linköping University, Sweden, Heidi.paltto@liu.se, http://www.ifm.liu.se/biology/ecology/conservation_ecology/heidi-paltto/

Björn Nordén, PhD, Norwegian Institute for nature research (NINA), Oslo, Norway

Tord Snäll, PhD, Swedish University of Agricultural Sciences (SLU), Uppsala, Sweden

Anna Nordberg, The Swedish Board of Agriculture, Jönköping, Sweden

Ingrid Thomasson, Sveaskog, Askersund

References:

Paltto, H., Nordberg, A., Nordén, B. & Snäll, T. 2011. Development of oak wood pastures into secondary woodland reduces the richness of rare epiphytic lichens. PLoS ONE 6(9):e24675. (freely available at: http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0024675 )

Paltto, H., Thomasson, I., Nordén, B. 2010. Multispecies and multiscale conservation planning: Setting quantitative targets for red-listed lichens on ancient oaks. Conservation Biology 24:758-768.