Elise Buisson

Old-growth grasslands assemble over millennia and support high biodiversity and many ecosystem services, but continue to undergo widespread destruction for production of crops, timber, and minerals. How biodiversity recovers after grassland destruction and the functional consequences of this recovery can be informed by plant functional traits—i.e., morpho-physiological features that influence growth, survival, and reproduction. Yet we lack understanding of how functional traits differ between old-growth and secondary (i.e., recovering) grassland plant species at the global scale, hindering understanding of community assembly processes that transcend geographical regions. Addressing this gap, we synthesized trait data for 742 plant species from 24 studies across six continents to understand how plant species indicative of old-growth and secondary grasslands compare in their traits. Compared to old-growth grasslands, plants indicative of secondary grasslands were taller and had leaves with more nitrogen content, higher specific leaf area, and lower dry-matter content. Notably, these trait differences that make old-growth grassland plants more resource conservative and secondary grassland plants more resource acquisitive persisted over a century. Taken together, these findings help to explain why many secondary grasslands support altered plant communities for decades to centuries and emphasize the importance of old-growth grassland conservation in the light of the unique plant forms and functions they support. Persistent trait shifts associated with grassland destruction could accelerate nutrient cycling, and our findings provide guidance for recovering old-growth grassland biodiversity through ecological restoration.

This chapter delves into a concise historical narrative describing the trajectory of our understanding of grassland degradation and early restoration attempts. Initial studies were often empirically done with a focus on woody component and later shifted toward more nuanced approaches that recognize the key roles of herbaceous species, disturbance, and ecosystem services. The chapter emphasizes the imperative need for frameworks tailored for grassland restoration and explores multiple shifts required to address contemporary challenges in grassland restoration. Drawing on ecological theory and scientific insights, the chapter advances an ongoing understanding of the multifaceted nature of grassland restoration and advocates for holistic approaches that protect biodiversity, provide ecosystem services, and support human livelihoods in global grasslands. Proposed principles for grassland restoration encompass policy frameworks, enhanced biological sourcing, developing appropriate site preparation and management, and the identification of suitable indicators to monitor restoration outcomes. Examples of successful restoration initiatives on tropical and temperate grassland restoration serve as illustrative benchmarks, showcasing tangible achievements and lessons learned in the restoration domain. Overcoming knowledge shortfalls and developing technology are instrumental to upscale grassland restoration to meet the demands of the UN Decade on Ecosystem Restoration and protect grassland biodiversity in the face of future climate change.

Grassland ecosystems have suffered significant degradation and restoring them is fundamental to fight against climate change and biodiversity loss. Fire is an important component in the evolution and management of grasslands worldwide and can potentially be used to restore grasslands. In this paper, we present a systematic literature review to know how fire has been used as a tool in grassland ecological restoration and its efficacy. To do that, we collected the results (positive, negative, or null) of fire treatments considering five restoration objectives: (1) increase biotic diversity, (2) remove woody biomass, (3) control exotic species, (4) promote abiotic changes, and (5) improve ecosystem services, and considering different major grassland types and how fire was employed. We discuss our results by summarizing the data, if fire was applied alone or combined with another technique, and considering major grassland types. Our review shows that fire has been used mainly to restore temperate grasslands in North America. Fire tends to yield more positive results than negative; however, the majority of results are null. Fire is highly effective at removing woody biomass, mainly in temperate and Mediterranean grasslands. Fire is also effective controlling exotic species, mainly when combined with other techniques, but it has low efficacy for exotic species control in tropical and subtropical grasslands. The efficacy in xeric grassland along different objectives is low. We conclude that the successful use of fire as a tool in grassland restoration is highly context‐dependent, varying according to grassland ecosystem type, restoration objectives, and techniques employed.

Tropical grasslands, savannas, and shrublands comprise open ecosystems that are experiencing growing anthropogenic pressures and lack theoretical and practical knowledge on ecological restoration. Natural regeneration in these ecosystems is very slow and often unfeasible, making planting and seeding increasingly important restoration techniques. We conducted a systematic review to investigate the richness, origin, and functional groups of the plant species used to restore tropical open ecosystems. Identifying species and their functional groups used in restoration experiments allows us to better plan, implement, and monitor restoration. We identified 220 plant species introduced to restore tropical open ecosystems in 37 controlled restoration sites located in Brazil, Australia, the USA, Kenya, Venezuela, South Africa, and Congo. Nearly 55% of plant species were shrubs or trees, and 80% were native to the country where they were used. Strikingly, 51% of the plants were used only once. We found no evidence of biotic homogenization in the restoration of tropical open ecosystems. Only six reintroduced species were classified as endangered, suggesting an untapped potential for enhancing conservation-oriented restoration. Our results indicate that despite the predominant use of native species, woody species remain disproportionately planted compared to herbaceous species, which constitute the bulk of diversity in grasslands and savannas.

Questions: Control of invasive species and seed addition are key steps in grassland restoration. Nevertheless, selecting seed mixes and seed quantities are hard tasks in restoration projects. An interesting idea is to design seed mixes using functional traits and create a community based on limiting similarity to overlap and outcompete the invader. We aimed to test the effect of two sown communities (one created to overlap the invader niche) and three seed sowing densities to reduce the performance of the invasive grass Eragrostis plana.Location: Greenhouse experiment in the Campos Sulinos grasslands region, Southern Brazil.Methods: We created a bifactorial experiment. The first factor was the sown community, each composed of nine native grasses but with different proportions: (1) Limiting, based on limiting similarity, and (2) Balanced, where all species were sown at the same seed weight. We used leaf functional traits (Specific leaf area, leaf area, leaf dry matter content ) to design the Limiting community. The second factor was the seed density of native species, sowing twice (1) 1 g/m², (2) 2 g/m², and (3) 4 g/m² (i.e., total density was 2, 4, and 8 g/m²). E. plana was sown once at 0.5 g/m². Above‐ground and below‐ground biomass of all species were collected after nine months to assess the treatment effects.Results: Biomass production of the invasive species was lower when sown with native species. Nevertheless, both sown communities did not differently affect the invasive biomass production. Higher seed density of native species resulted in lower invasive above‐ground biomass, but not below‐ground biomass. Three native species did not germinate, consequently, the established communities were quite different from those designed.Conclusions: The low species germination limited our discussion about the use of limiting similarity to design seed mixes. High seed sowing density is a better approach when defining sowing strategies to compete with invasive grasses.