Trees are the main carbon (C) stocks in boreal forests, but the understory vegetation can contribute significantly to total C balance. In northern boreal pine forests, understories consist of variable habitats with different roles for C balance: often, the understory is a combination of warmer and drier sunlit patches dominated by lichens and more shaded and moister patches dominated by mosses and dwarf shrubs. These habitats are influenced by herbivores that may control canopy and understory vegetation, soil C cycling and, consequently, forest C balance.
We studied how excluding large herbivores (Rangifer tarandus and Alces alces) for short and longer period affects understory CO2 fluxes across sunlit and shaded habitats in a boreal forest. We measured understory CO2 fluxes with manual and automated chamber methods across sunlit and shaded habitats in grazed and ungrazed areas over the growing seasons of 2019 and 2020. We used fences that had excluded large herbivores for one year and for 25 years alongside the adjacent grazed area at Oulanka research station in northeastern Finland.
We found that CO2 release increased in shaded habitats when large herbivores were excluded for one year. On the other hand, when large herbivores were excluded for over two decades, CO2 fluxes decreased to some extent, and this was independent of a habitat type. Our findings suggest that impacts of large herbivores on CO2 fluxes may vary over time and be opposite in short term compared to long term. Considering these temporal variations in grazing impacts may help to forecast C fluxes more accurately, which may be relevant for informed climate solutions.
The article is open access and you can find the full text here.
Reference: Kantola, N., Väisänen, M. Leffler, A.J., Welker, J.M. Contrasting impacts of short- and long-term large herbivore exclusion on understory net CO2 exchange in a boreal forest. Ecography
https://doi.org/10.1111/ecog.06724
Text and photograph: Noora Kantola, University of Oulu