Several European teams studied second-growth forests over 4 years and were able to show their beneficial effects in terms of biodiversity and their resilience in the face of droughts. The findings are compiled in a series of six articles published in the journal Annals of Forest Science*.

As part of the European Green Deal—which aims to make Europe carbon neutral in 2050—the European Union is planning to make considerable efforts to plant trees and restore damaged or depleted forests. However, to date the planned actions largely neglect the restoration potential of second-growth forests resulting from the spontaneous reforestation of abandoned rural areas. Yet, this is a common phenomenon across Europe. In fact, the European Commission’s projections estimate that 4.2 million hectares of agricultural areas will be abandoned by 2030. The spontaneous reforestation of these areas could be a very cost-effective and attainable method to foster multifunctional and diverse landscapes, especially in places where active management is not possible. Europe was the first continent in the world to achieve the “forest transition”, meaning that it has undergone a turnaround from diminishing to increasing forest cover as early as in the 19^th century. During the last decades, Europe has experienced the most important gain in forest cover in the world—estimates range from 8,000 km² per year since the 1990s to 28,300 km² per year between 1982 and 2015. However, to fully exploit the potential of second-growth forest for landscape management and conservation in Europe, it is necessary to have a better understanding of the biological mechanisms underlying the phenomenon. With this purpose, several European teams have joined the ERA-NET BiodivERsA3 project SPONFOREST, coordinated by INRAE, a research project that aims to better understand the establishment and functioning of second-growth forests in Europe.

Understanding the biological mechanisms of second-growth forest establishment

Researchers studied second-growth forests in 5 rural and periurban landscapes from southwest Europe (France and Spain). Their results illustrate the great complexity and context-dependence of spontaneous forest establishment.

Among the various results obtained, the researchers were able to show that the establishment of second-growth forests promotes the defragmentation of pre-existing forests as well as the proliferation of new patches, both in forest-dominated and open landscapes. Contrary to previous assumptions, they detected no link between increasing forest cover and the loss of landscape-scale habitat diversity. The researchers also observed that the diversity and heterogeneity of unmanaged second-growth forests promote insect diversity in fragmented landscapes. Their “wild” nature—with different tree ages and unsystematic exploitation—helps moreover enhance their resistance to drought.

Spontaneous forest establishment is a widespread phenomenon, in Europe and other places around the world. Understanding this phenomenon is key to untapping its full potential, in order to improve the management and conservation of the European landscapes affected by ongoing farmland abandonment, biodiversity loss and climate change.

*Annals of Forest Science is one of the ten scientific journals owned by INRAE and is edited by Springer https://www.springer.com/journal/13595

References

Ruiz-Carbayo H., Pino J., Bonal R. et al. Insect herbivory in novel Quercus ilex L. forests: the role of landscape attributes, forest composition and host traits. Annals of Forest Science 77, 32 (2020). https://doi.org/10.1007/s13595-020-00934-4

Palmero-Iniesta M., Espelta J.M., Gordillo J. et al. Changes in forest landscape patterns resulting from recent afforestation in Europe (1990–2012): defragmentation of pre-existing forest versus new patch proliferation. Annals of Forest Science 77, 43 (2020). https://doi.org/10.1007/s13595-020-00946-0

Alfaro-Sánchez R., Valdés-Correcher E., Espelta J.M. et al. How do social status and tree architecture influence radial growth, wood density and drought response in spontaneously established oak forests?. Annals of Forest Science 77, 49 (2020). https://doi.org/10.1007/s13595-020-00949-x

Villellas J., Martín-Forés I., Mariette S. et al. Functional distance is driven more strongly by environmental factors than by genetic relatedness in Juniperus thurifera L. expanding forest stands. Annals of Forest Science 77, 66 (2020). https://doi.org/10.1007/s13595-020-00973-x

Gerzabek G., Oddou-Muratorio S., Hampe A. Recruitment of a genotyped Quercus robur L. seedling cohort in an expanding oak forest stand: diversity, dispersal, and performance across habitats. Annals of Forest Science 77, 78 (2020). https://doi.org/10.1007/s13595-020-00979-5

Lamonica D., Pagel J., Valdés-Correcher E. et al. Tree potential growth varies more than competition among spontaneously established forest stands of pedunculate oak (Quercus robur). Annals of Forest Science 77, 80 (2020). https://doi.org/10.1007/s13595-020-00981-x

Hampe A., Alfaro-Sánchez R., Martín-Forés I. Establishment of second-growth forests in human landscapes: ecological mechanisms and genetic consequences. Annals of Forest Science 77, 87 (2020). https://doi.org/10.1007/s13595-020-00993-7

Contact:
Arndt Hampe (Send email)
Joint Research Unit for Biodiversity, Genes and Communities - BIOGECO
INRAE-Université de Bordeaux)