Reverence for the Dark Garden

By Eric R. Eaton:

Gardens are places of peace and comfort for us during our waking hours. The bright colors and lush fragrances of blooming flowers feed our senses, and foliage and fruits nourish our bodies. What we forget is the necessity of truly dark nights to make that possible. We may be asleep inside our homes, but outside, we continue to illuminate the landscape. Research has shown that even dim lighting can have a negative impact on plants, pollinators, and other organisms necessary for gardens to prosper.

ILLUSTRATION BY CRISTINA BENCINA

Artificial light at night (ALAN) is problematic in many ways. Organisms have evolved over eons to expect, and rely on, cycles of daylight and darkness, and seasonal variations in the angle of the sun, with corresponding changes in day length. Sunlight also conveys a broad spectrum of wavelengths that artificial lights do not. Lunar cycles account for natural nocturnal illumination but, again, plants and animals have evolved with that. Detection of photoperiod by plants is crucial to proper timing of budding and flowering. Bloom at the wrong time, and appropriate pollinators may not be present to achieve fertilization.

Light pollution is the easiest of all environmental problems to solve, at least technically. The effects of turning off superfluous lighting would be immediate.” ~Johan Eklöf

Detection of photoperiod by the plant’s phytochromes, and suppression and inducement of flowering, are influenced and disrupted mostly by light in the red and far-red end of the spectrum, which corresponds to that emitted by high-pressure sodium lights. LED lights skew heavily toward the blue end of the spectrum, where cryptochrome and phototropins, plant photoreceptors responsible for regulating circadian rhythms, germination, direction of growth, and development, operate. To complicate matters, triggers for botanical behaviors are not always related to light receptors, nor are they the same for every species. There are often other environmental cues involved, and/or other physiological processes unrelated to light perception.

Night sky from the bottom of the Grand Canyon, February 2023. Flagstaff, AZ was the first city to receive Dark Sky status, in 2001. It banned all advertising spotlights in 1958. PHOTO: Sophie Macaulay

There is more. Some urban trees may retain their leaves longer when exposed continuously to artificial light at night. This is especially true for poplars, willows, and American Elm. Some plants require a period of darkness to recover from environmental stresses such as air pollution. Frequently, it does not require a high intensity of light, or exposure to artificial light over a long duration, to trigger changes in plant biology.

Surprisingly, little research has focused on the impact of artificial lights on agricultural crops, but the anecdotal evidence is startling. A brightly-lit prison in Ohio resulted in abnormal, stunted growth of soybeans in an adjacent field. High-pressure sodium lights installed along a road in Accra, Ghana resulted in the failure of maize crops to flower, even after the plants exhibited more rapid growth.

Animal life suffers, too. Nocturnal insects are exposed to more predation from spiders, bats, and birds. Aquatic species like mayflies, confused by amplified polarized light, lay eggs on surfaces other than water, dooming their offspring. Diurnal insects die prematurely because their activity periods are overextended. Firefly mating flashes are overwhelmed. Nighttime navigation by starlight is no longer possible. Even minimal heat from bulbs can kill insects.

In The Darkness Manifesto, recently translated into English, Swedish bat scientist and writer Johan Eklöf points to phenomena ranging from the “vacuum cleaner effect”, whereby city, suburban, and rural bright lights act as seductive magnets for insects, upsetting entire ecosystems (Insect Collapse), to the disruption of predation, mating rituals and reproduction of fish, turtles, and even bioluminescent dinoflagellates (“sea fire”) in the oceans. The many birds, bats and other animals that rely on dark hours for feeding and safety are forced further back into the shadows.

A 2001 study cited in the British Ecological Society’s Journal of Ecology found that almost nineteen percent of the Earth’s terrestrial surface, excluding Antarctica, was impacted by light pollution. In a 2017 study light pollution was estimated to increase at least 2 percent per year globally. In urbanized areas, the extent is far greater. Light pollution is not merely excessive lighting. It can be glare, exceptionally bright light that causes visual discomfort and disorientation. Skyglow is the overall brightening of the night sky over human settlements. The influence of skyglow extends beyond city limits, well into rural and wilderness regions. Over 80% of the world’s population lives under skyglow. Light trespass describes light falling where it is unnecessary, or beyond where it is intended.

One response to light pollution has been the proliferation of dark sky initiatives. The platform has been driven largely by astronomers and stargazers, though ornithologists are now advocating severe reductions in city lighting at least during bird migration periods. Concern over declines in insect abundance and diversity are driving entomologists to jump on the bandwagon.

Dark sky actions at the community level mostly involve instituting outdoor lighting ordinances, or demanding better enforcement of existing regulations. Education of the citizenry is also necessary. People are largely unaware of the adverse effects of light pollution. Currently, only eight locations in Colorado have dark sky certification: Black Canyon of the Gunnison National Park, Dinosaur National Monument, Great Sand Dunes National Park & Preserve, Jackson Lake State Park, Hovenweep National Monument, the cities of Norwood, Ridgway, Westcliffe and Silver Cliff. But this doesn’t mean other places in the Centennial State lack lighting ordinances.

There are steps we can take as individual homeowners, business proprietors, and citizens to diminish the impacts of ALAN. We can endorse those dark sky initiatives for one thing. Maybe we can remove decorative outdoor lighting. Consider replacing outdoor “security” lights with motion-sensitive fixtures. Fixtures that direct light straight down are less impactful than lights directed outwards, upwards, or otherwise disperse light over a wide area. Simply adding a shield to an existing fixture can reduce light trespass. Draw blinds or curtains to keep indoor lighting indoors, minimizing its impact outside.

Our economic ecosystem is largely responsible for the problem. Advertising, public safety, infrastructure illumination, after-dark labor shifts, and entertainment all demand lighting, usually of high intensity. Is it all necessary? We have adapted to the Edison-illuminated norms that have existed for centuries now, but at what cost? Have we lost our reverence for the sacred night? Can we recapture the magic of darkness, instead of fighting against it?

Eric R. Eaton is principal author of the Kaufman Field Guide to Insects of North America and writes the blog “Bug Eric.”