Reforestation Consequences

Global warming affects the carbon balance of the world’s ecosystems, and warming is more pronounced in high latitudes [1]. In these northern latitudes, Boreal and Arctic ecosystems provide essential uptake and storage of carbon [2].

Afforestation is perceived as a straightforward solution to counterbalance our excessive carbon dioxide output. Increasing productivity in areas of previously deforested areas has the potential to provide a consistent, low maintenance sink for emissions. Around 60% of boreal deforestation has been compensated for with subsequent reforestation between 2003 and 2012 [2]. This reforestation can be optimised for boreal clearings.

Global warming advances biological spring and delays onset of winter, providing a longer growing season and providing negative feedback to global warming through increased atmospheric carbon uptake [3]. This means that a rejuvenated boreal forest could have a more significant positive effect on our global climate for longer.

Increasing the broadleaved components in managed boreal forests could be an option for optimisation. Broadleaved trees may reduce the risk of devastating forest fires that can release enormous quantities of carbon into the atmosphere through smoke and soot [4]. In comparison to coniferous trees, broadleaved species are often lighter. They can positively contribute to increasing boreal forest albedo and reflecting more of the sun’s radiation away from the surface of the planet [4].

Efforts for reforestation must remain targeted towards specific areas to prevent unintended costs to the planet. For example, planting at the northern edge of the boreal forest may replace snow which would otherwise have provided positive albedo [4]. Plantation forestry can have a significant adverse effect on biodiversity in areas where native shrubs and plants grow, so focusing on degraded habitats would be needed to minimise these effects [5].

While increased productivity has the potential to provide a sink for carbon, in the arctic tundra, this effect is overshadowed by the release of stored carbon stocks buried in the soil [6][7]. Warmer temperatures can facilitate succession of Arctic tundra ecosystems by woody shrubs and trees [7]. This effect can be attributed to an increased association with ectomycorrhizal fungi. These fungi release peroxidases into the soil to release Nitrogen, and by extension, carbon [6].

Warming temperatures also raises the incidence of extreme weather events such as storms and flooding [8]. These events, as well as others like freeze-thaw cycles and pests and pathogens, contribute to reducing productivity and thus, carbon uptake [8].

Snow accumulates in arctic ecosystems that have undergone succession to shrubland. This can provide an insulative layer that increases surface temperature and therefore, microbial action over winter [6]. The increase in albedo can somewhat counterbalance the effect of snow insulation, but once forest succeeds shrub albedo will decrease once again [2].

The MET office predicts an average global temperature increase in 2020 of 1.1oC from preindustrial levels. We are fast approaching the 1.5oC limit set in the Paris Agreement that is crucial to minimising the damage of climate change [9]. Plans from the World Economic Forum to plant 1 trillion trees have been proposed as a mitigation measure, but this approach has tunnel vision to the counterintuitive effects of planting inappropriately [10].

Further research into reforestation projects and arctic greening it needed to maximise carbon capture and storage in these regions. Acting pre-emptively, on the base assumption that more trees is better could be fruitless and even detrimental to future action.

[1]  IPCC, 2018: Global warming of 1.5°C. An IPCC Special Report on the impacts of global warming of 1.5°C above pre-industrial levels and related global greenhouse gas emission pathways, in the context of strengthening the global response to the threat of climate change, sustainable development, and efforts to eradicate poverty [V. Masson-Delmotte, P. Zhai, H. O. Pörtner, D. Roberts, J. Skea, P.R. Shukla, A. Pirani, W. Moufouma-Okia, C. Péan, R. Pidcock, S. Connors, J. B. R. Matthews, Y. Chen, X. Zhou, M. I. Gomis, E. Lonnoy, T. Maycock, M. Tignor, T. Waterfield (eds.)]. In Press.
[2] Alkama & Cescatti (2016) Biophysical impacts of recent changes in global forest cover. Science 351, 600-604.
[3] Peñuelas, J., Rutishauser, T. and Filella, I (2009) Phenology Feedbacks on Climate Change. Science 324, 887-888.
[4] Astrup, R., Bernier, P.Y., Genet, H., Lutz, D.A. and Bright, R.M., 2018. A sensible climate solution for the boreal forest. Nature Climate Change, 8(1), pp.11-12.
[5] Bremer, L.L., Farley, K.A. Does plantation forestry restore biodiversity or create green deserts? A synthesis of the effects of land-use transitions on plant species richness. Biodivers Conserv 19, 3893–3915 (2010). https://doi.org/10.1007/s10531-010-9936-4
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[7] Parker, T.C., Subke, J.-A., and Wookey, P.A. (2015). Rapid carbon turnover beneath shrub and tree vegetation is associated with low soil carbon stocks at a subarctic treeline. Glob Change Biol 21, 2070–2081.
[8] Bjerke, J.W., Karlsen, S.R., Høgda, K.A., Malnes, E., Jepsen, J.U., Lovibond, S., Vikhamar-Schuler, D., and Tømmervik, H. (2014). Record-low primary productivity and high plant damage in the Nordic Arctic Region in 2012 caused by multiple weather events and pest outbreaks. Environ. Res. Lett. 9, 084006
[9] Carrington, D. (2020). Climate crisis fuels year of record temperatures in UK, says Met Office. [online] The Guardian. Available at: https://www.theguardian.com/uk-news/2020/jan/03/climate-crisis-fuels-year-of-record-temperatures-in-uk-says-met-office [Accessed 10 Feb. 2020].
[10] Calma, J. (2020). Planting 1 trillion trees might not actually be a good idea. [online] The Verge. Available at: https://www.theverge.com/2020/1/31/21115862/davos-1-trillion-trees-controversy-world-economic-forum-campaign [Accessed 10 Feb. 2020].