Study Sets a Clearcutting Limit to Protect Boreal Forest Birds

A study led by the University of Jyvaskyla in Finland has defined, for the first time, an ecological threshold for how much clearcutting boreal forests can sustain. Clearcutting, the practice of felling all the trees in an area at once, is common worldwide in boreal forests but is also a significant factor behind the decline of forest biodiversity, though the long-term, landscape-level effects of accumulated clearcutting had not been well understood until now.

Researchers analysed Finland's national bird-monitoring data from 2006 to 2020, together with European maps of forest disturbance showing accumulated clearcut areas, across southern and central Finland. Senior researcher Remi Duflot of the University of Jyvaskyla said the abundance of common forest bird species, and of species specialised in old-growth forests, was lower in landscapes where large areas of clearcutting had built up over 20 years.

The study defines what the researchers call a safe operating space: the ecological limit below which populations of old-growth specialist birds can stay stable or recover from past declines. Based on the results, Duflot said clearcutting should not exceed about 10 per cent of a forest landscape over any 10-year period to maintain forest bird populations, which corresponds to a forest rotation period of about 90 years, or to excluding roughly a fifth of forest areas from clearcutting altogether.

The researchers caution that ecological thresholds can vary by region and by which group of organisms is studied; lichens and mosses, for instance, may be more sensitive than forest birds, so the results should be supplemented with studies of other species groups before general thresholds are adopted. Professor Mikko Monkkonen of the University of Jyvaskyla said the findings give forest owners and forestry decision-makers a clear, easily communicated goal for reconciling forest use with biodiversity protection, and that the method is suitable for use in other parts of the world too.