In the heart of our rapidly urbanizing world, the subtle interplay between natural and artificial factors shaping plant life cycles is gaining unprecedented attention. Recent groundbreaking research published in Nature Cities reveals that artificial light at night (ALAN) exerts a more significant influence than temperature on extending the growing seasons of urban vegetation. This discovery challenges longstanding ecological models that have predominantly attributed shifts in plant phenology—the timing of life cycle events—to changes in temperature driven by climate change. The implications of this work ripple through our understanding of urban ecosystems, biodiversity, and even global carbon cycles.
For decades, ecologists and climate scientists have regarded temperature as the primary driver of plant phenology, observing that warmer temperatures generally signal earlier leaf-out and delayed senescence. However, in densely populated cities where artificial lighting saturates the night environment, the picture becomes more complex. Artificial lighting, from street lamps to illuminated billboards, introduces an entirely different set of environmental cues that can disrupt or override natural rhythms. Wang, Meng, and Richardson et al. have now provided compelling evidence demonstrating that ALAN not only impacts but surpasses temperature effects in influencing urban growing seasons.
The study leverages extensive satellite remote sensing data combined with ground-based observations collected across multiple metropolitan areas. By analyzing Normalized Difference Vegetation Index (NDVI) trends, a proxy for plant greenness and productivity, researchers could detect subtle shifts in the onset and duration of growing seasons. Intriguingly, urban zones exposed to higher intensities of nighttime artificial lighting exhibited notably prolonged growing seasons compared to less illuminated peri-urban or rural counterparts, even when climatic conditions were similar.
Mechanistically, the research elucidates that plants perceive artificial lighting akin to an extension of daylight, disrupting their circadian and photoperiodic responses. In natural settings, photoperiod—the length of day versus night—is a critical determinant for timing phenological changes, ensuring synchronization with seasonal resource availability and avoiding frost damage. However, when nights are artificially illuminated, the conventional dark period shortens, confusing plant sensors that rely on dark intervals to trigger dormancy or senescence. Consequently, photosynthetic activity can continue later into the calendar year, effectively lengthening the growing season.
This phenomenon is especially pronounced in urban tree canopies and ornamental vegetation, which often experience intense direct exposure to ALAN. Extended photosynthetic periods not only alter carbon assimilation but can also affect resource allocation within plants, potentially influencing growth form, reproductive output, and susceptibility to pests and diseases. The cumulative impact of these shifts on urban plant communities could cascade to affect food webs, urban wildlife habitats, and ecosystem services such as air purification and temperature regulation.
One striking dimension of the study is its challenge to the predictive capacity of existing phenological models. These models, which guide climate change impact assessments and urban planning decisions, largely neglect the role of urban lighting environments. By integrating ALAN as a critical variable, researchers advocate a paradigmatic shift toward more nuanced models that consider both abiotic and anthropogenic influences on urban ecosystems. This is crucial as cities increasingly dominate terrestrial landscapes and as urban greenery gains prominence in sustainability agendas.
Moreover, the authors highlight potential feedback loops involving ALAN and urban warming. While temperature elevates metabolic rates and can hasten plant development, extended illumination maintains physiological activity during periods normally reserved for rest. This can exacerbate the urban heat island effect by sustaining transpiration and evapotranspiration processes over longer timeframes. Conversely, altered phenology may influence carbon sequestration dynamics, possibly redefining urban contributions to greenhouse gas fluxes.
The research also prompts a reevaluation of urban lighting policies. Municipalities worldwide have adopted increasingly sophisticated LED street lighting systems for energy efficiency and safety, but these technologies can exacerbate spectral characteristics that perturb biological systems. By demonstrating that ALAN outweighs temperature effects in phenological timing, the authors call for ecologically informed lighting designs that mitigate biological disruptions while balancing human needs.
Importantly, the study distinguishes between different wavelengths of light, underscoring that blue-rich white LEDs are particularly potent in eliciting phenological shifts. This spectral sensitivity aligns with plant photoreceptors such as cryptochromes and phytochromes, which mediate light perception and circadian regulation. Future urban lighting infrastructure could leverage this knowledge to favor spectra less disruptive to vegetation, paving the way for light pollution mitigation strategies in green urban planning.
Furthermore, the study touches upon broader ecological consequences, including possible changes in invasive species dynamics. Non-native plants that can exploit extended growing seasons may outcompete native flora, reshaping community composition and ecosystem resilience. Additionally, altered flowering times driven by ALAN may decouple plant-pollinator interactions, threatening pollination services and the subsequent reproduction of diverse plant species.
At the global scale, this research adds a new dimension to the discourse on human-induced environmental change. While climate warming dominates the narrative, the role of pervasive light pollution deserves increased scrutiny as a modifying agent of plant phenology. Urban centers, currently home to more than half of humanity, create unique biophysical environments where human activity directly reprograms natural cycles.
Finally, Wang, Meng, and Richardson et al. call for interdisciplinary collaborations that integrate urban ecology, photobiology, urban planning, and public policy. Addressing the complexities of ALAN’s ecological impact will require novel experimental designs, improved monitoring technologies, and inclusive policy frameworks that reconcile urban development with biodiversity conservation goals.
As the findings permeate scientific and public consciousness, they underscore an urgent need to reimagine how cities interface with natural systems. Artificial light at night, once viewed merely as an aesthetic or safety feature, emerges as a potent ecological force capable of reshaping plant life cycles on a planetary scale. Managing this influence thoughtfully represents both a challenge and an opportunity for creating sustainable urban futures that harmonize technological progress with the imperatives of nature.
Subject of Research: The influence of artificial light at night (ALAN) and temperature on the lengthening of urban growing seasons.
Article Title: Artificial light at night outweighs temperature in lengthening urban growing seasons.
Article References:
Wang, L., Meng, L., Richardson, A.D. et al. Artificial light at night outweighs temperature in lengthening urban growing seasons. Nat Cities (2025). https://doi.org/10.1038/s44284-025-00258-2
Image Credits: AI Generated
