Challenges and directions for open ecosystems biodiversity restoration: An overview of the techniques applied for Cerrado

1. Ecological restoration of tropical open ecosystems remains challenging for both science and practice. Over the last decade, innovative techniques have been developed, but whether they have been successful or not remains to be demonstrated. Assessing the outcomes of these initiatives is crucial to drive the following steps to improve tropical grasslands and savanna restoration.

2. Analyzing 82 data sets from the literature and primary data collection, we assessed the effectiveness of passive and active restoration techniques applied in Cerrado open ecosystems. We used plant diversity variables (species and growth forms) as indicators, considering ruderals and exotics as non-target species. Specifically, we aimed to answer: (i) How does the diversity of target species change through time in areas subject to passive restoration? (ii) Are active and passive restoration techniques effective in restoring the proportion of target species found in old-growth reference ecosystems? (iii) Have the current techniques been successful in recovering the proportions of growth forms of reference ecosystems?

3. We found that target species proportions do not increase with time, suggesting limitations of typical species to colonize degraded sites. Hence, passive restoration will promote the conservation of a limited and constant number of target species. This number will depend on the magnitude of degradation and previous land use.

4. The restoration techniques currently applied to restore the biodiversity of Cerrado open ecosystems are not reaching the reference standards, with distinct techniques driving plant communities to different sets of growth forms. Active restoration based on propagules obtained from pristine donor sites (topsoil translocation, plant material transplant, and seeding) performed better than passive restoration for most of the growth forms analyzed.

5. Synthesis and Applications: Different growth forms have different roles in determining the structure and functioning of Cerrado vegetation. A mix of techniques can better approximate plant diversity and the proportionality of target species of pristine ecosystems. Singular restoration approaches are insufficient for restoring Cerrado open ecosystem biodiversity. Mixed efforts encompassing various techniques are required instead. Furthermore, it is likely restoration success can be improved with greater investment in improving our understanding of and developing existing restoration techniques.