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Beyond climate
Summary
This review pulls together research on how city life—things like compacted soil, pollution, road salt, artificial night lighting, and even microplastics—affects the growth rings and internal structure of urban trees, not just the usual suspects like temperature and rainfall. The takeaway matters because trees are one of our best tools for cooling cities and cleaning air, so understanding what's stressing them out helps cities plant and care for trees in ways that keep these health benefits coming. Notably, this is an early attempt to seriously consider how microplastics might be affecting tree biology, an area that's still poorly understood.
Urban trees are increasingly exposed to persistent anthropogenic drivers that extend beyond climatic forcing and fundamentally alter the conditions of secondary growth. While climatic controls of cambial phenology and xylogenesis are well established, the mechanisms by which non-climatic drivers regulate cambial activity and wood formation remain fragmented and are often inferred only indirectly. Here, we develop a cambium-centred framework to synthesise current evidence on how anthropogenic drivers shape wood formation in urban and peri-urban trees. To our knowledge, this is among the first syntheses explicitly linking anthropogenic drivers to distinct stages of xylogenesis. Anthropogenic drivers are typically chronic, spatially heterogeneous, and temporally decoupled from seasonal climatic rhythms, and may alter cambial kinetics and generate anatomical signatures not captured by ring width alone. We evaluate major driver domains, including root-zone constraints, altered hydrology, urban microclimate, pollution, salinity, and mechanical disturbance, while also considering emerging drivers such as artificial light at night and microplastics. Evidence is stratified into three levels: direct observations, indirect physiological evidence, and mechanistic plausibility. Across driver classes, three recurrent anatomical patterns emerge: reduced conduit size under hydraulic or osmotic stress