Small seeds and large knowledge gaps: understanding the regeneration traits of Brazilian savannah grasses necessary for restoration

BACKGROUND AND AIMS: Grasses (Poaceae) dominate the herbaceous layer of the species-rich Brazilian savannah (Cerrado), driving ecosystem functioning and fire regimes while facing severe threats from land-use conversion and cultivation of invasive forage grasses. Despite the recent expansion of ecological restoration and native grass seed production, knowledge gaps still hinder their use in savannah restoration. We conducted a scoping review to (i) map information and knowledge gaps related to regeneration traits of Cerrado grasses, (ii) evaluate trait coverage of species used in restoration projects, (iii) examine whether commercially available grasses represent a functionally homogeneous subset, and (iv) assess how ecological knowledge informs seed-based restoration. METHODS: Following PRISMA-ScR guidelines, we screened 315 records identified, spanning seven regeneration niche phases (pre-dispersal, dispersal, germination, emergence, establishment, initial growth, and vegetative persistence) across 45 primary studies on native Cerrado Poaceae. A complementary dataset catalogued 24 grass species commercialized by two major native seed producers. KEY RESULTS: We identified 90 traits across 108 species (24 commercial). Germination traits dominated studies (85 species; 26 studies), while emergence, establishment, and initial growth remain severely understudied. Only 11 studies integrated ≥3 phases, and none covered >4. We found marked functional diversity across key regeneration traits, including seed mass, germinability and dispersal period. Contrary to expectations, commercially available species did not form a functionally homogeneous subset, but largely overlapped with non-commercial species, capturing broad functional variation. However, knowledge of commercial species is concentrated in a few taxa. CONCLUSIONS: Our scoping review revealed a strong bias towards germination traits in Cerrado grasses, with limited integration across other phases. Despite this, grasses are far from functionally uniform, showing substantial variation in regeneration strategies. Methodological variation across studies limits comparability and integration into ecological inference, leading to seed-based restoration practices that often rely on species whose key regeneration traits remain poorly understood.