[PhD defence] 26/08/2025 - Natalia De Freitas Medeiros: "Restoration of open biomes: evidence, gaps and threats associated with tree planting" (UMR IMBE)

Ms Natalia DE FREITAS MEDEIROS will publicly defend her thesis entitled "Restoration of open biomes: evidence, gaps and threats linked to tree planting", directed by Ms Elise BUISSON and co-supervised with the "Universidade Federal de Minas Gerais" (Brazil), on Tuesday 26 August 2025 at 1:00 pm.

Laboratory

• UMR 7263 - IMBE Mediterranean Institute of Biodiversity and Marine and Continental Ecology

Composition of the jury

Mrs Elise BUISSON	Avignon University	Thesis supervisor
Mr Fernando A.O. SILVEIRA	Universidade Federal de Minas Gerais	Thesis co-director
Ms SOIZIG LE STRADIC	INRAe, University of Bordeaux	Examiner
Mr Jerônimo SANSEVERO	Universidade Federal Rural do Rio de Janeiro	Examiner
Ms Giselda DURIGAN	Instituto de Pesquisas Ambientais do Estado de São Paulo	Rapporteur
Mr Gerhard OVERBECK	Universidade Federal do Rio Grande do Sul	Rapporteur

Summary

Restoration of open ecosystems is difficult because of misdirected restoration actions, a general lack of knowledge about how to improve ecosystem resilience, and uncertainties about how to measure restoration success in an ecologically relevant way. Active interventions are often required to promote the recovery of these ecosystems, and long-term monitoring and management is recommended, as regeneration rates are often extremely slow. Tree-based practices based on carbon storage have become widespread in many ecosystems, whether forested or open. However, the consequences of tree planting are not yet fully understood. For example, tree planting programmes often overestimate the potential to increase carbon sequestration, while largely overlooking the negative impacts on biodiversity and ecosystem services. With the aim of improving restoration, particularly that of open ecosystems, this thesis aims to fill certain gaps and bring together the accumulated knowledge on the subject in order to guide future restoration actions.

In the first chapter of this thesis, I assessed the overall impact of tree planting on the biodiversity of closed and open ecosystems through a meta-analysis. I found an overall reduction of 71 % in plant, vertebrate and invertebrate biodiversity compared with reference ecosystems, but an increase of 55 % compared with degraded sites. The planting of trees increased biodiversity compared with the degraded sites, but without reaching the levels of biodiversity observed in the reference ecosystems. This pattern remained constant when we examined the effects of tree planting on biodiversity according to different types of plant cover, the origin of the species planted and the planting techniques. In the second chapter, I sought to understand where and how the restoration of tropical open ecosystems has been implemented. Through a systematic review, I found that the studies were largely context-dependent. The use of restoration techniques varied inconsistently between sources of degradation, and less than half of the indicators assessed were monitored consistently over time. In addition, due to significant data quality issues, I propose a checklist for the minimum information to be reported in research, as well as a standardised, more comprehensive and multilingual guideline. In the third chapter, I explored the species planted and sown in restored tropical open ecosystems, and found that most were native to the restored ecosystem. However, grasses and forbs were relatively under-represented compared to trees and shrubs.

Finally, in the fourth chapter, I conducted a field study to understand the effects of tree invasion in areas adjacent to pine plantations. I found that the cover of native herbaceous plants decreased as tree cover increased, and that the same pattern was found for the richness and frequency of herbaceous species, as well as for the richness and abundance of plant-pollinator interactions. Overall, this thesis reveals that current restoration approaches often rely heavily on tree planting, which may only partially restore biodiversity and potentially harm herbaceous communities and plant-pollinator interactions in open ecosystems.

Keywords restoration, open biomes, review, tropical grasslands