Functional Plant Diversity: Traits, Evolution, Biodiversity Conservation and Ecosystem Restoration

Ecological restoration is increasingly expected to deliver several ecosystem functions at once and to remain effective under a changing climate. Functional diversity, meaning the variety and distribution of organismal traits that govern responses to the environment and effects on ecosystem processes, has therefore been proposed as a design principle for choosing which species to reintroduce. This review critically examines whether the evidence supports that proposition. The review covers terrestrial vegetation restoration, with brief reference to animal communities, and synthesises literature published from January 1997 to 27 July 2026, identified through searches of multidisciplinary scholarly indexes, citation tracking and authoritative institutional standards. Four conclusions emerge. First, trait-based selection is conceptually mature, and trait–environment matching improves establishment in several well-replicated seeding and planting programmes, but whether particular traits favour or impede success depends strongly on context, and some findings conflict directly. Second, the positive relationship between plant diversity and ecosystem multifunctionality is robust in controlled experiments, yet in restored and naturally assembled communities the dominant traits, expressed as community-weighted means, frequently explain ecosystem functions better than trait dispersion does, and trade-offs among functions limit simultaneous optimisation. Third, theory and experiments support an insurance role for response diversity under drought, but evidence from young tree-diversity experiments shows that diversity can stabilise outcomes without raising average survival, and that positive diversity effects may reverse under extreme drought when drought-sensitive species dominate. Fourth, implementation is constrained less by theory than by seed and nursery supply, sparse trait data for regional floras, intraspecific variation, and short monitoring periods. The review concludes that functional diversity is best treated as a conditional design heuristic whose value depends on explicit functional targets, knowledge of dominant species' traits and climate-informed sourcing, rather than as a quantity to maximise. Priorities include long-term, multi-site restoration experiments that manipulate trait composition and dispersion independently, trait-to-fitness models validated under future climate analogues, and joint research with seed producers and practitioners.