Spontaneous native–non-native tree mixtures worldwide: a systematic map of research patterns, with knowledge gaps and management implications

Raquel Juan-Ovejero , Estefanía Suárez-Vidal, Noela Carrera, Guillermo Velo-Antón, María Calviño-Cancela, Verónica Ferreira

Purpose of Review: Spontaneous mixtures of native and non-native tree species occur in forest landscapes affected by land-use change, species introductions and disturbances. However, research on these communities remains fragmented.

Recent Findings: We identified 238 cases. Research was concentrated in high-income countries and studies included diverse combinations of native and non-native tree species. Land abandonment was the most frequently reported driver in tropical moist forests, whereas urbanization, forest management, land abandonment and nearby non-native tree plantings were more evenly represented in temperate forests. Research focused primarily on forest composition, structure, regeneration and dynamics, with comparatively limited attention to functional traits, soil properties, ecosystem functioning and associated biodiversity. Approximately two-thirds of cases relied on single-time assessments, while studies incorporating both native and fully non-native reference forests as reference conditions were uncommon.

Summary: Spontaneous native–non-native tree mixtures involve diverse species combinations and develop under different ecological and land-use contexts. Our findings highlight the need for context-dependent forest management that considers species characteristics, potential ecological impacts, land-use history and landscape conditions, rather than biogeographical origin alone.