Nordic studies show the significance of old-growth forests for biodiversity
Researchers at the University of Eastern Finland conducted a systematic review of 99 scientific publications that compared the flora or fauna of old-growth forests, managed forests and clearcut sites in boreal Europe. The reviewed studies showed large differences in the species communities inhabiting these forest types.
The studies analysed for the systematic review show that the species richness of full-canopy forests increases as the forest gets older. Clearcut sites are also species-rich, but they are inhabited by a distinct set of species in comparison to full-canopy forests.
The studies had examined several species groups that cover a large part of the flora and fauna inhabiting forests, including birds, epiphytes (i.e., lichens and bryophytes growing on tree trunks), fungi and insects inhabiting deadwood, soil fungi, ground-dwelling invertebrates, other insects and understory vegetation.
Birds, epiphytes and fungi and insects in deadwood were more diverse in older forests. Understory vegetation and insects other than those inhabiting deadwood were more diverse in younger forests, especially clearcut sites. There were few studies on soil fungi.
The flora and fauna characteristic of old-growth forests are associated with old or dead trees. Such species are rare or absent in forests in commercial use.
“In managed forests, trees are cut down before they grow old or die, and thus old and dead trees are scanty in them. Leaving a portion of the trees standing during clearcutting would be an effective solution, but only very few of these so-called retention trees are left in harvests,” says Doctoral Researcher Aleksi Nirhamo from the University of Eastern Finland.
Clearcut sites are inhabited by species associated with open habitats and young forests. Conditions on clearcut sites are very different from full-canopy forests, and thus they are inhabited largely by distinct sets of species.
Even though the flora and fauna of clearcut sites are rich in certain species groups, they are degraded habitats.
“Early stages of forest succession would be formed without clearcuts by disturbances such as storms. These kinds of habitats differ from clearcut sites for example by having huge amounts of deadwood that is missing from clearcut sites,” Nirhamo points out.
“Additionally, the treeless stage of succession is cut short by the planting of conifers, which also homogenises the tree species composition of the regenerating stand,” he continues.
At the moment, there is a great abundance of habitat in the Nordic countries for species inhabiting clearcut sites. For the species of old-growth forests, the situation is worse.
“Forest habitats are modified widely in order to enhance wood production, which homogenises and degrades them,” Nirhamo says.
“Especially old and dead trees are abundant and versatile only in forests that have remained unharvested for long, and thus there is little space for species dependent on those resources.”
Source: University of Eastern Finland
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