An extensive study carried out collaboratively by the University of Helsinki and Natural Resources Institute Finland demonstrates that the plant community of a forest stand can thoroughly change after regeneration cutting, even when the number of species remains more or less unchanged. The change is evidenced as the appearance and increase of grasses and herbaceous species as well as decrease of typical forest species immediately after regeneration cutting.
Researchers from the University of Helsinki and Natural Resources Institute Finland (Luke) investigated how forest management practices affect understory plant communities of forests both in the short term and over decades.
The study utilised a forest understory dataset compiled by Luke, covering all of Finland. This unique repository consists of more than 600 forest sites surveyed at 10-year intervals in 1985, 1995 and 2006.
In these 10-year windows, the researchers assessed the rate of change of the vascular plant community, which is composed of dwarf shrubs, grasses and herbs.
Species numbers do not change, species do
The researchers observed that despite considerable turnover in species identity, the number of species in the sample plots remained relatively constant in the decade-long periods, regardless of when and how the forest had been managed. On average, the number of species arriving and lost from plots were roughly in balance.
According to Elina Kaarlejärvi, postdoctoral researcher at the University of Helsinki's Research Centre for Ecological Change, the loss and arrival of species are at their highest after regeneration cutting. Then the most abundant species especially in fertile forest sites were replaced by other species. Regeneration cutting includes clear-cutting, seedtree cutting and shelterwood cutting.
"Exploring forest stands of different ages, we found that the arrival of new species and the disappearance of old ones were connected with a change in the abundance of dominant species, all the way up to 60-year-old forest stands. In forests older than that, bilberry and lingonberry had achieved the status of permanent dominant species in their communities and new arriving species no longer impacted their dominance," Kaarlejärvi adds.
Marked change in fertile sites - Knock-on effects unknown
"For the forest undergrowth, regeneration cutting entails a transition from a stable community to a series of changes, which takes decades in fertile sites," summarises Tiina Tonteri, a research scientist at Luke.
According to the researchers, the findings indicate that if regeneration cutting becomes increasingly common, our most common forest plants, bilberry and lingonberry, will cover a smaller proportion of forests.
Professor Anna-Liisa Laine, director of the Research Centre for Ecological Change, says that rapid and extensive changes in vegetation are very likely to have knock-on effects on ecological functions, such as the nutrient cycle, as well as on other species that interact with plants, such as pollinators.
"There is a pressing need to understand which factors alter our species communities, and what the ecosystem level effects of this biodiversity change are. For this purpose long-term ecological datasets such as this one collected by Luke are irreplaceably valuable," Laine points out.
Reference:
Elina Kaarlejärvi, Maija Salemaa, Tiina Tonteri, Päivi Merilä, Anna-Liisa Laine:
Temporal biodiversity change following disturbance varies along an environmental gradient.
Global Ecology and Biogeography.
