Retention patches maintain diversity of epiphytic and epixylic indicator lichens more effectively than solitary trees

ABSTRACT

The effectiveness of retention trees and patches in preserving diversity of nine epiphytic and epixylic old-growth forest lichens was studied in north boreal spruce forests in Finland. We compared (1) 7–8-year-old retention cuts, with at least 5–10 living or dead retention trees per hectare, (2) 10–12-year-old clear-cuts, with some scattered living and dead retention trees on the sites, (3) old-growth spruce forests, and (4) 7-8-year-old retention patches (0.06–0.45 ha) representing the original tree species composition of old-growth forests. The occurrence of indicator lichens was studied on 150 deciduous trees and snags in each forest category. The species richness was significantly higher in old-growth forests than in the clear-cuts and retention cuts, but did not differ between old-growth forests and retention patches. Only three species were found in clear-cuts and two in retention cuts. Foliose cyanolichens Leptogium saturninum and Nephroma bellum thrived on solitary retention trees, whereas humidity-requiring pin lichens from the genus Chaenotheca were found only in old-growth forests and retention patches. Our results suggest that the ability of epiphytic and epixylic species to survive on retained trees depends on several factors: (1) substrate quality (tree species, tree type and diameter of a tree), (2) environmental factors (e.g. humidity, slope exposition), and (3) morphological and physiological characteristics of species. Besides of substrate trees, the retained conifers (esp. spruce) seem to be important in retention patches to provide the shading necessary to maintain humidity.

KEYWORDS:

• Epiphytic lichens
• boreal forests
• retention trees
• retention patches
• calicioid lichens
• cyanolichens

Acknowledgements

We are grateful to Pekka Halonen for his help in selecting target species for investigating lichens; Johanna Kähkönen, Veera Luolavirta, Jarno Kemppainen, Pirjo Kuusela, and Veikko Seppälä for their help in fieldwork; Kari Viertola for his help with the figures, and Richard Foley for checking the language of the manuscript.

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

The research was financed by the Finnish Forest Research Institute, Rovaniemi Research Station (presently: the Natural Resources Institute Finland).