Red-listed boreal species are in trouble as forested PAs become more isolated

Human-induced habitat fragmentation through intensive forestry practices is affecting the structure of boreal forests in northern Europe. Protected areas can be viewed as the last islands of old and mature growth forest habitats in a matrix of even aged, rotationally clear-cut forest landscape.
Published in Earth & Environment
Red-listed boreal species are in trouble as forested PAs become more isolated
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Increasing loss of mature boreal forests around protected areas with red-listed forest species - Ecological Processes

Background Protected areas (PA) are central to biodiversity, but their efficiency is challenged by human-induced habitat loss and fragmentation. In the Fennoscandian boreal region, forestry with clearcutting is a threat to biodiversity causing the loss of mature forest elements and deterioration of ecological processes in forest landscapes, ultimately affecting PAs via declined structural connectivity. This paper aims to (1) determine PAs with high, red-listed species concentrations; (2) estimate the change in forest habitat around these PAs on different spatial scales; and (3) determine if forest management intensity is higher around biologically most valuable PAs. Occurrences of red-listed forest-dwelling species in Finland were used to identify PAs harbouring these species and to produce site-specific importance indices. CORINE landcover data was used as a baseline for the distribution of forests to assess the cover of clear-cuttings from 2001 to 2019 with the Global Forest Change (GFC) data set in three buffer areas around the PAs with occurrences of red-listed species. Results The largest proportion of clear-cuts occurred in 1 km and 10 km buffers around the PAs in the southern and middle boreal zones, being ca. 20%. This indicates that the forest habitat is degrading fast at regional and landscape levels. On the positive side, the change in forest cover was lower around the biologically most important PAs compared to other PAs with red-listed species. Conclusions Open and free satellite-data based assessments of the cover and change of forests provide reliable estimates about the rates at which mature and old-growth forests are being converted into young managed ones in Finland mainly via clear-cuts on different scales around PAs. The rate of clear-cuts was lowest in adjacent buffer areas next to the most species-rich PAs, which provides opportunities for biodiversity conservation efforts to be targeted to the remaining mature and old-growth forests found in the vicinity of these areas.

If you take the nearly 1000-kilometre-long train trip from Helsinki, the capital of Finland on the northern shore of the Gulf of Finland in the Baltic Sea, all the way to Kolari, the northernmost train station still in use, and look out the window at almost any point of the journey, it is likely that the scenery flashing by the window alternates between seedlings of planted trees, middle aged trees in neat rows and clear-cut openings. As the train voyages northwards through the southern, middle and finally to the northern boreal zone, and the landscape gets more rugged, the decreasing productivity of vegetation is mirrored by the tree compositional changes from mixed spruce dominated forests towards more abundant pine forests in the landscape.

Planted seedlings, clear cut opening with soil scarification and mature, managed forest nearing harvest age in 2019. ©Raimo Virkkala

Finland, and Fennoscandia in general, lies almost completely in the boreal biome, which is generally considered as one of the most intact biomes in the world. However, in this area, forests have long been intensively managed and deployed for wood extraction. Forestry is the main driver affecting boreal species in Northern Europe, and many of them have become red-listed or declined due to habitat degradation. As almost all forests outside the protected area (PA) network are under management, these species are forced to live in an increasingly fragmented landscape.

The patchwork of different management stages alternating in the landscape, observed from the train window, becomes even more evident when viewed from above. Aerial images and space-borne remote sensing effectively reveal the extent of habitat transformation. In our study, we opted to use this point of view to investigate how intensively the surrounding forests have been managed around biologically important protected areas during the past couple of decades. This is an important question in the light of national and international conservation targets and agreements, that call for not only the expansion of protected spaces but also representativeness and connectedness of these additions to the current PA network.

We gathered a dataset, including 864 red-listed forest species that primarily inhabit mature or old-growth forests, to see how many of these species' occurrences were recorded in PAs. For each PA, we calculated a species importance index that reflected its’ conservation value. Our index reflected the rarity of each species’ observations in relation to the full set of all species observations, i.e., how many observations a given species had in the data. Next, using CORINE landcover data as a baseline and Global Forest Change (GFC) as land-cover change data, we identified the areas where a forest that is close to the end of the rotation cycle, or existing old-growth and mature forest, was clear cut during the years 2001-2019 around the PAs with valuable forest species occurrences. These analyses were done for 100m, 1km and 10km buffers around the PAs.

National land survey of Finland aerial image of a train track going through a managed boreal forest landscape in central Finland

Our results showed that the largest proportion of clear cuts, ca. 20%, occurred in the landscape and regional scales around PAs in the southern and middle boreal zones. At this rate, nearly all forests outside PAs might be clear-cut during a 70–100-year rotation cycle, leaving many species in trouble as climate change forces them to search for new areas of sufficiently suitable living conditions. We compared the PAs with the top 5% scores of species importance to other PAs with red-list species and noticed that the change in forest cover was lower around the biologically most important sites – this suggests that there may still be potentially useful forest stands available next to present PAs for the enlarging of the PA network. Improving structural connectivity is especially urgent in the southern boreal zone, where PAs are small and rotation cycles are short. An effective strategy to improve the permeability of the managed forest matrix for species requiring structural elements of old-growth forests and humid microclimates would be to increase such elements, e.g., the amount of dead wood and large retention trees all through the forest management cycle.

This piece of research is part of a project that aims to assess boreal forest biodiversity in the PA network in Finland and promote informed climate-wise conservation planning. We are currently working on a follow-up paper, where we include climate change velocity estimates in biologically valuable PAs and discuss climate-wise planning strategies that could help forest species survive under the joined pressures of land use and climate change. While there might not even be a final station on the pursuit of enhancing the state of biodiversity in the intensively managed boreal forests, and the track is undoubtedly not straight forward, it is crucial that everyone gets onboard.

References:

Määttänen, AM., Virkkala, R., Leikola, N., Heikkinen RK. (2022) Increasing loss of mature boreal forests around protected areas with red-listed forest species. Ecol Process 11, 17. https://doi.org/10.1186/s13717-022-00361-5d

Tikkanen OP, Martikainen P, Hyvärinen E, Junninen K, Kouki J (2006) Red-listed boreal forest species of Finland: associations with forest structure, tree species, and decaying wood. Ann Zool Fenn 43:373–383

Virkkala R, Lehikoinen A, Rajasärkkä A (2020) Can protected areas buffer short-term population changes of resident bird species in a period of intensified forest harvesting? Biol Conserv 244:108526. https://doi.org/10.1016/j.biocon.2020.108526

Funding:

This work was supported by funding provided by the Finnish Ministry of the Environment (Evaluating the protected area network in the changing climate, SUMI, and the Finnish Ecosystem Observatory, FEO), and the Strategic Research Council (SRC) at the Academy of Finland (Decision No 312559).

Poster image: ©Riku Lumiaro

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