Which provides 'better' ecosystem services, natural forests or plantations?

The ES in ForES project stands for ecosystem services but which type of forest do we consider to provide 'better” ecosystem services, natural forests or plantations? Our post-doc Francesco Martini looks at the question...

Fig 1. Comparisons of ecosystem services between natural forests and plantations. The top two photos are two Sitka spruce plantation, while the bottom two show mixed forests.

The 2020s is the UN Decade of Ecosystem Restoration and efforts to restore degraded ecosystems, including forests, are growing. Replanting forests in previously forested areas (i.e., reforestation) or planting completely new forests where there were none before (i.e., afforestation) is scaling up globally.

A key question, then, is what is the best way to conduct reforestation and afforestation

projects so as to develop resistant and resilient forests, capable of delivering multiple ecosystem services, and what are the trade-offs?

As many forest restoration schemes strongly rely on species-poor plantations, is it really the best option? Do ecosystem services delivered by plantations, including monocultures, equal those delivered by natural and more diverse forests? A considerable body of research exists on this key question but results have not been adequately summarised.

A study published in 2022 in the journal Science attempted to answer this debate. Gathering data from over 250 studies distributed around the world, the authors compared the quantity of five ecosystem services delivered by plantations as opposed to natural forests (e.g., naturally regenerated forests): aboveground carbon storage, water provisioning, soil erosion control, biodiversity, and wood production.

Perhaps unsurprisingly, the authors found that natural forests perform better than plantations for most ecosystem services (Figure 1). Naturally regenerated forests are more biodiverse, provide better soil erosion control and larger water yield, and store more aboveground carbon. However, if the goal is timber production for commercial use, plantations do indeed produce more value. Importantly, results were consistent across forest types, from tropical to temperate forests.

Depending on the management objectives when restoring or replanting a forest, it is important to consider the trade-offs involved. While plantations, especially monocultures, are productive and can yield high economic returns in the form of timber products, many of the ecosystem services provided by more diverse and native forests risk being reduced.

Ireland set the goal to continuously increase forest cover to reach 18% by 2050. In doing so, the Government is aiming, among many objectives, to expand the coverage of mixed forests with native species, to protect ancient woodlands and native biodiversity, and to increase access to public forests. All while, at the same time, increasing timber production for domestic use. Meeting these ambitious goals would increase the benefits of the ecosystem services provided by Irish forests.

References

Hua, F.Y., Bruijnzeel L. A., Meli P., Martin, P.A., Zhang, J., Nakagawa, S., Miao, X., Wang, W., McEvoy, C., Pena-Arancibia, J.L., Brancalion, P. H.S., Smith, P., Edwards, D.P., Balmford, A., 2022. The biodiversity and ecosystem service contributions and trade-offs of forest restoration approaches. Science, 376, 839–844. doi: 10.1126/science.abl4649

Ireland Forest Strategy 2022-2030, Draft for public consultation.

UN Environment Programme, FAO, UN Decade on Ecosystem Restoration,

www.decadeonrestoration.org