Hello everyone!
As I have mentioned in my previous post, I will be diving into how light pollution affects plants. We all know that plants depend on light for photosynthesis to produce their own food. So shouldn’t increase light allows plants to photosynthesize more and produce more chemical energy for growth and other functions? Well, that is what we hope to happen. Light pollution can actually affect plants’ cycle directly and also indirectly by affecting their pollinators.
Many cactus species bloom only at night and the famous Queen of the Night blooms only one night a year and wilts by dawn (Beyond Science, 2018). If you are interested, do check out this video by Chris Kridler which shows her blooming and closing.
Plants like these are directly affected by increased lighting as it might prohibit them from ever flowering and thus reproducing.
Most night lighting does not have the intensity to affect photosynthesis but it might affect trees that are sensitive to day length, which is the duration of daylight (Chaney, 2002). Artificial lighting, especially ones that emit in the red to the infrared range has the ability to ‘convince’ plants that day length is longer. This can change flowering patterns and also promote continued growth which prevents leaves from falling and developing dormancy for winter. This can result in trees being more susceptible to ice damage which can shorten the tree’s life. The picture below is a tree in Amagansett, New York which shows how the leaves nearer the streetlamp have not fallen.
In addition, trees growing near lights tend to break bud and flower earlier in the spring (Kramer, 2016) which makes them vulnerable to ice damage as well. These trees run the risk of losing their entire reproductive effort which can thus mess up their relationship with pollinators.
Artificial lighting is also capable to influence the way plants grow. Leaves grown under continuous lighting tend to be larger in size thus more stomatal pores that remain open for a longer time (Chaney, 2002). This makes the plants more susceptible to pollution and drought.
Many experimental studies have shown artificial lighting can have physiological effects on plants under controlled conditions. Researchers found that artificial lighting was able to change the species composition of grassland communities in a natural vegetation community (Bennie et al, 2017). Some species responded well to artificial lights, producing more biomass and showing higher seed production thus pushing out other species. This has a huge implication on biodiversity conservation, especially in urban areas.
Such effects on plants will be carried forward and impact insects and birds that rely on them for food or shelter which further causes an imbalance in the ecosystem. Furthermore, artificial lighting is also affecting nocturnal pollination. There has been a 62% reduction in visits to plants as compared to darker areas which result in an overall 13% reduction in fruit production (Knop et al, 2017). This reduction is fruits also means a reduction of food source not just for us but for the wildlife too and thus a vicious cycle is created.
Artificial lighting be it directly or indirectly, is more than capable of affecting plants in various ways than we have imagined. For us, lighting up is a way of convenience and something so easy to do, however, the consequences are much more than we can handle. Therefore, from now on though it may be a small act, switch off your lights when it is not in use and help save a tiny leaf from your action!
That brings me to the end of this post!
See you guys soon!
References
Bennie, J., Davies, T. W., Cruse, D., Bell, F., & Gaston, K. J. (2017). Artificial light at night alters grassland vegetation species composition and phenology. Journal of Applied Ecology, 55(1), 442-450. doi:10.1111/1365-2664.12927
Beyond Science. (2018, May 24). Queen of the Night: The Flower That Only Blooms ONE Night A Year. Retrieved September 03, 2020, from https://www.beyondsciencetv.com/2018/05/23/queen-of-the-night-the-flower-that-only-blooms-one-night-a-year/amp/
Chaney W. (2002) Does Night Lighting HarmTrees? Forestry and Natural Resources, 1-4.
Knop, E., Zoller, L., Ryser, R. et al. Artificial light at night as a new threat to pollination. Nature 548, 206–209 (2017). https://doi-org.libproxy1.nus.edu.sg/10.1038/nature23288
Kramer, S. (2016, June 29). Light pollution is making trees do something strange. Retrieved September 04, 2020, from https://amp.insider.com/trees-bloom-early-because-light-pollution-2016-6
RyanLee
September 6, 2020 — 5:24 pm
Hello Naomi!
Thank you for illuminating (pun intended) us with this tidbit on how the little things we do can actually cause issues to natural cycles of our flora and fauna. It is interesting to note that trees have their own cycle which can be affected by lighting as seen in that image of New York. I have never thought that it would be an issue since Singapore does not exactly have seasons.
One question that I would like to ask is this, are there any ways that we can reduce our impacts on roadside trees like that in the picture? While turning off the light at home is doable, turning off streetlamps could endanger people who may be travelling at night. Does changing to lights with lower intensity make a difference? I do hope that we can save all the leaves since we do not want to cause a vicious cycle!
From,
Pollutant de Jure
https://blog.nus.edu.sg/pollutantdejure/
Naomi
September 7, 2020 — 8:06 am
Hi Ryan!
Thanks for the question!
Indeed different types of light emit different wavelengths of light that have different impacts. Based on what I know, those that emit red to infrared are more likely to cause a potential impact on trees as they are the ones that are able to ‘convince’ plants of longer daylight. These lights include incandescent and high pressure sodium lights which fun fact, was what Singapore was using for a long time before switching to LED. Therefore, changing to other types of lights could help reduce the potential effects on plants indeed.
However, with that being said, it is also important to ensure that shielding fixtures are placed on the lamps such that light is directed in the right direction away from the trees. In addition, dimming lights can also be considered during off-peak hours to avoid continuous lighting. This not only can reduce light pollution but also save resources.
Though Singapore is now using LED, which seemed to be a better option in this sense, in both energy savings and effects on plants. But LEDs are much brighter bulbs and capable of causing more significant sky glow which is known to affect animals and even humans. The effects on animals can then again cause an indirect impact on the trees which once again establishes a vicious loop cycle.
It is hard to quantify the effect of light pollution with so many factors in play and everything being inter-connected with each other. I think it is definitely important to always be aware and try to reduce pollution as much as possible such that effects can be limited. Proper urban planning I feel is very important such as choosing the right plant species.
Hopefully, I answered your questions and gave you more information on this situation! Glad to have this discussion with you! 🙂