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Beyond Climate: A Cambium-Centred Synthesis of Anthropogenic Drivers of Wood Formation in Urban Trees
Summary
This review paper looks at how city life—things like pollution, road salt, artificial light at night, and even microplastics in the soil—affects how trees grow their wood, not just weather and climate. Understanding this matters because urban trees under constant stress may become weaker or less resilient over time, which affects their ability to cool our neighborhoods, clean the air we breathe, and support the leafy green spaces linked to better mental and physical health. While the microplastics angle is still an emerging area with limited direct evidence, it's a signal that pollution's reach into the natural systems we rely on may be broader than we realized.
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; anomalies in wall deposition under carbon limitation or oxidative stress; and pronounced circumferential heterogeneity under spatially localised forcing. Integrative approaches combining xylogenesis monitoring, quantitative wood anatomy, dendrometer observations and spatially explicit sampling are essential to disentangle anthropogenic from climatic effects and improve assessment of tree resilience.