Christmas lights harm plants

As Christmas approaches, cities around the world are decorated with colorful Christmas lights, creating a visual spectacle that attracts residents and tourists alike. Many cities compete to be the best and during the holidays they transform into dazzling places with streets, squares, parks and gardens bathed in colorful light.

However, although this tradition is aesthetically attractive to many, it raises questions about its impact on the environment, particularly on urban flora.

Changes in plant physiology and behavior due to Christmas lights

The metabolism of most plants and animals is closely related to the light cycle. Therefore, the effect of Christmas lights would not exactly create a “festive climate” for plant species.

Many plant behaviors, such as when they germinate and when they shed their leaves, depend on photoperiod, the number of hours of light per day, or more precisely, the variation in the number of hours of light day by day. .

As the photoperiod increases, the days become longer and spring arrives, the optimal time for germination; while in autumn the days with daylight become shorter, which means the photoperiod shortens and the plants enter a dormant phase.

Therefore, artificial night light induces changes in the life cycle of plants and in the signaling of their photoreceptors regarding budding and senescence of leaves and flowers.

When plants are artificially illuminated with points of light very close to their leaves, the photoperiod perceived by the plant changes, as does its phenology. These changes can, in turn, affect leaf germination and slow their color change.

A study conducted by Lin Meng of Iowa State University and published in the journal Proceedings of the Academy of Natural Sciences In 2022, artificial night light was found to accelerate the appearance of leaf buds by almost 9 days on average and slow the color change process by about 6 days.

They may seem like small changes to our eyes, but they will alter important plant functions and ecosystem services.

Some plant species are more sensitive to the artificial light of Christmas lights at night. In 2021, Professor Benedikt Speisser and colleagues from the University of Konstanz found that some invasive species increase their biomass in response to light pollution, which can lead to faster spread than in urban areas.

Christmas lights

Relationship between plants and animals

When the budding or flowering process changes, an imbalance in coordination between insects and plants can occur, so this type of night lighting has implications for relationships in the urban ecosystem.

For example, if pollinators are not synchronized with flowering, plant reproduction is affected. Species that rely on nocturnal insects may lose their ability to pollinate as animals interpret their nocturnal behavior based on available light. If a tree is lit, do not go near it.

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It is worth remembering that interactions between animals and plants are essential for maintaining healthy ecosystems. Since artificial night lighting significantly alters these dynamics, its consequences will have a greater than expected impact on the evolution of trophic flows.

According to a study by Dirk Sanders and his colleagues at the University of Exeter in the United Kingdom, published in the journal Scientific Reports in 2015, depending on the nature, light significantly influences the behavior of some aphid species, reducing their populations by 20% over 5 generations. Although the effects of these insects are harmful to plants as they consume their sap, they also act as pollinators and compete with other, even more harmful pests.

If the balance of this relationship is disturbed, the biomass of infected plants decreases significantly. This shows that the effects of artificial night lighting extend throughout the food chain and have far-reaching effects on entire ecosystems.

A new approach to Christmas lighting

There is no doubt that Christmas lights are a real spectacle for children and adults and serve as a tourist attraction. However, available scientific evidence suggests that while these are ancient and visually stunning traditions, they may have unintended negative impacts on urban vegetation.

If we want to avoid this damage, it is necessary to rethink the type, intensity and location of Christmas lighting and to look for less invasive and more sustainable lighting solutions that balance Christmas with the protection of the urban environment.

Choose softer lighting, perhaps focusing on iconic buildings and monuments rather than highlighting trees or other forms of vegetation. Critical reflection and technological advances can create a Christmas tradition that respects and protects the health of our urban ecosystems.

References:

  • Macgregor, CJ et al. 2019. Effects of street lighting technologies on pollination success and quality in a night-pollinated plant. Ecosphere.
  • Meng, T.-T. et al. 2022. Influence of light at night on the phenology of woody plants. Urban forestry and urban greening.
  • Parker, E. T. et al. 2011. Primordial synthesis of amines and amino acids in a Miller H2S-rich spark discharge experiment from 1958. Proceedings of the National Academy of Sciences, 108(14), 5526-5531. DOI: 10.1073/pnas.1019191108
  • Sanders, D. et al. 2015. Nocturnal changes in aphid and parasite population dynamics. Royal Society Open Science.
  • Singhal, R.K. et al. 2019. Responses to artificial night light pollution in plants. Journal of Plant Physiology.
  • Speißer, O. et al. 2021. Biomass responses of widespread and less widespread alien plants to nighttime light pollution. Global Ecology and Biogeography.

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