All-night streetlights can make leaves inedible to insects: What a new study says

All-night streetlights can make leaves inedible to insects: What a new study says

Subject: Env

Sec: Pollution

Context:

Artificial lights that run all night, such as streetlights, can make leaves grow so tough that insects cannot eat them, which could threaten urban food chains, according to a new study. The study, ‘Artificial light at night decreases leaf herbivory in typical urban areas’.

How was the study carried out?

• The researchers wanted to examine how artificial lights impact the relationship between plants and insects.
• To do so, they focused on two common species of street tree in Beijing: Japanese pagoda and green ash trees.
• Although these trees are similar in many ways, Japanese pagoda trees have smaller, softer leaves which insects prefer to munch on.
• To evaluate the impact of light on their traits such as size, toughness, water content, and levels of nutrients and chemical defence compounds.
• If the leaves were larger, it would mean that plants directed their resources (such as nutrients, water, and energy) to growth.
• If the leaves were tougher and contained high levels of chemical defence compounds like tannins, it would indicate that the resources were allocated for defence.
• The researchers observed that for both species of trees, the higher the levels of illuminance, the tougher the leaves.
• The tougher the leaves, the less evidence of insects eating them. The researchers found no sign of insects munching on leaves in areas which were lit the brightest at night.
• Artificial lights altered the levels of nutrients and chemical defence compounds in the leaves that were analysed.
• Japanese pagoda trees which were exposed to more artificial light had lower levels of nutrients such as phosphorus in their leaves. Such leaves had less evidence of insects consuming them.

Findings:

Trees exposed to artificial light at night might be extending their photosynthesis cycle. This can be really stressful for them as when a plant photosynthesises, it takes in energy, and if it does that all the time, the situation can be overwhelming and eventually kill the plant.

Light Pollution:

• Light pollution can be defined as the introduction by humans, directly or indirectly, of artificial light into the environment.
• Avoidable light pollution refers to light flow emitted at night by artificial light sources which are inappropriate in intensity, direction and/or spectral range, unnecessary to carry out the function they are intended for, or when artificial lighting is used in particular sites, such as observatories, natural areas or sensitive landscapes.

Types of Light pollution:

1. Light trespass: When unwanted light enters one’s property, for instance, by shining over a neighbour’s fence.
2. Over-illumination: It is the excessive use of light.
3. Glare: Glare is often the result of excessive contrast between bright and dark areas in the field of view.
   1. Blind glare: describes effects such as that caused by staring into the Sun. It is completely blinding and leaves temporary or permanent vision deficiencies.
   2. Disability glare: describes effects such as being blinded by an oncoming cars lights, or light scattering in fog or in the eye reduces contrast, as well as reflections from print and other dark areas that render them bright, with significant reduction in sight capabilities.
   3. Discomfort glare: does not typically cause a dangerous situation in itself, and is annoying and irritating at best. It can potentially cause fatigue if experienced over extended periods.
4. Clutter: Clutter refers to excessive groupings of lights. Groupings of lights may generate confusion, distract from obstacles (including those that they may be intended to illuminate), and potentially cause accidents. Clutter is particularly noticeable on roads where the street lights are badly designed, or where brightly lit advertising surrounds the roadways.
5. Skyglow: refers to the “glow” effect that can be seen over populated areas.

• It is the combination of all light reflected from what it has illuminated escaping up into the sky and from all of the badly directed light in that area that also escapes into the sky, being scattered (redirected) by the atmosphere back toward the ground.

Impact of light pollution:

• Wastes Energy and Money:
  • Lighting that emits too much light or shines when and where it’s not needed is wasteful. Wasting energy has huge economic and environmental consequences.
• Disrupting the ecosystem and wildlife:
  • Plants and animals depend on Earth’s daily cycle of light and dark rhythm to govern life-sustaining behaviours such as reproduction, nourishment, sleep and protection from predators.
  • Scientific evidence suggests that artificial light at night has negative and deadly effects on many creatures including amphibians, birds, mammals, insects and plants.
    • Ex: A study has now shown how nocturnal dung beetles are forced to search for cues in their immediate surroundings when they can no longer navigate using natural light from the night sky.
    • The effect of light in the form of fire or lamps attracting migratory and non-migratory birds at night, especially when foggy or cloudy, has been known since the 19th century and was and still is used as a form of hunting. The reasons for disorientation of birds through artificial night lighting are not well known. Experts suggest that the navigation of birds using the horizon as orientation for the direction is disrupted by lighting and sky glow.
• Harming human health:
  • Like most life on Earth, humans adhere to a Circadian Rhythm — our biological clock — a sleep-wake pattern governed by the day-night cycle. Artificial light at night can disrupt that cycle.