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

Plant functional ecology has long described species by mean trait values, yet individuals of the same species differ markedly in morphology, physiology and phenology. This within-species variation arises from phenotypic plasticity, genetic differentiation among populations, transgenerational effects and developmental change, and it is increasingly recognised as a determinant of how plants, communities and ecosystems respond to climate warming, altered precipitation, nutrient enrichment and other global change drivers. Existing reviews have treated the magnitude of intraspecific trait variation, the evolutionary ecology of plasticity and the community-level partitioning of trait change largely in separate literatures, which has left the links between them insufficiently examined. This critical narrative review synthesises peer-reviewed evidence identified through structured searches of multidisciplinary scholarly indexes, supplemented by backward and forward citation tracking, and appraises it by study design, spatial and temporal scale, and inferential strength. Four principal conclusions emerge. First, within-species variation is substantial but strongly trait-, scale- and context-dependent, so general rules about when it can be ignored remain provisional. Second, plasticity frequently shifts trait values in directions consistent with buffering, but evidence that these shifts are adaptive, sufficient in magnitude or sustainable under novel and extreme conditions is limited. Third, local adaptation is common in plants, and resurrection and transplant studies document contemporary evolution, yet several experiments indicate adaptational lag under recent warming. Fourth, intraspecific trait shifts often contribute as much as species turnover to changes in community-weighted trait means, particularly for leaf chemical and economic traits, but their effects on ecosystem functioning are inconsistent. Unresolved questions concern the separation of plastic from genetic responses in natural populations, the fitness consequences of trait shifts, the persistence of transgenerational effects, and the geographical concentration of evidence in temperate and boreal systems. Integrating within-species variation into distribution models, genomic forecasts and restoration planning is promising, but these applications require validation against independent field performance data. The evidence supports treating intraspecific variation as a conditional, measurable component of functional diversity rather than as either negligible noise or a universal buffer against environmental change.