Reinmann and Hutyra (1) measured an increase in aboveground forest growth and biomass at temperate oak forest edges (0–10 m) compared with the interior (20–30 m). When scaling their results up to the region of southern New England, they obtained an increase in aboveground carbon (C) uptake (13%) and C storage (10%) when forest edges were considered. They stated that current approaches used to quantify regional and global C budgets may underestimate C sequestration in forests.
We applaud the authors for conducting research in forest edges, which are still understudied despite their ample occurrence in present-day fragmented landscapes. However, when the impact of the edge effect on C sequestration is scaled up, results of our studies suggest that belowground C storage at forest edges should also not be neglected. Remy et al. (2) measured an increase in C and nitrogen (N) stocks in both mineral soil (30%) and roots (48%) up to 30 cm deep in temperate broadleaf and coniferous forest edges (0–8 m) in Belgium and Denmark compared with the forest interior (128 m).
Furthermore, Reinmann and Hutyra (1) suggest a potential interaction between land-use change (i.e., forest fragmentation) and climate change through responses on forest growth. We looked into the interaction of land-use change with N deposition, another driver of global change. Remy (3) observed that the edge conditions (increased solar radiation, higher soil temperatures, higher atmospheric deposition, lower forest floor C/N ratios, and higher litter input) increased the abundance of litter- and soil-dwelling detritivorous fauna, which, in turn, stimulated N cycling processes, via increased litter decomposition and mineralization rates. Furthermore, forest edges affected gaseous C and N cycles via an increased uptake of methane and a decreased emission of nitric oxide (4). Consequently, edge-specific conditions not only stimulate forest growth but also increase above- and belowground C and N storage through altered N cycling.
Several other researchers had already highlighted the impact of N deposition on C sequestration. De Vries et al. (5) obtained a soil response of 10–30 kg of C per kg of N under a total N deposition of 10–25 kg⋅ha−1⋅y−1, and Janssens et al. (6) showed that enhanced N availability indirectly increased soil C storage by reducing organic matter turnover.
In concordance with Reinmann and Hutyra (1), our findings underline the need to include forest edge effects in programs and models monitoring forest C changes, since they may cause substantial additional amounts of C storage, both above- and belowground.
Acknowledgments
This research was funded by the Fonds Wetenschappelijk Onderzoek Flanders (Project G046413N).
Footnotes
The authors declare no conflict of interest.
References
- 1.Reinmann AB, Hutyra LR. Edge effects enhance carbon uptake and its vulnerability to climate change in temperate broadleaf forests. Proc Natl Acad Sci USA. 2017;114:107–112. doi: 10.1073/pnas.1612369114. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 2.Remy E, et al. Strong gradients in nitrogen and carbon stocks at temperate forest edges. For Ecol Manage. 2016;376:45–58. [Google Scholar]
- 3.Remy E. 2017. Nitrogen cycling and sequestration in temperate forest edges. PhD thesis (Ghent University, Ghent, Belgium)
- 4.Remy E, et al. Edge effects on N2O, NO and CH4 fluxes in two temperate forests. Sci Total Environ. 2017;575:1150–1155. doi: 10.1016/j.scitotenv.2016.09.196. [DOI] [PubMed] [Google Scholar]
- 5.De Vries W, et al. The impact of nitrogen deposition on carbon sequestration by European forests and heathlands. For Ecol Manage. 2009;258:1814–1823. [Google Scholar]
- 6.Janssens IA, et al. Reduction of forest soil respiration in response to nitrogen deposition. Nat Geosci. 2010;3:315–322. [Google Scholar]