NIGHT SKY AND DARK ENVIRONMENTS: BEST MANAGEMENT PRACTICES FOR ARTIFICIAL LIGHT AT NIGHT ON BLM-MANAGED LANDS TECHNICAL NOTE 457 33 Amphibian behavior and circadian rhythm responds to day length (photoperiodism). Laboratory experiments suggest that artificially lit environments affect larval development and behavior in some species of frogs and toads (Buchanan 2006; Wise 2007). Some of these effects are likely related to suppressed melatonin production. Artificial light at night also may affect emergence and foraging behavior of various frog species that are active only under extremely dark conditions (Buchanan 2006). 3.5.2 Effects of Artificial Light at Night on Plants Plants use light as a source of energy and information. Light controls plant growth and other functions by providing the energy needed for photosynthesis and by triggering or inhibiting a variety of important processes, such as leaf drop, bud development and flowering, seed germination, and stem elongation (Gaston et al. 2013). Artificial light at night can potentially cause photosynthesis to occur at night, but this is unlikely an important issue on BLM-managed lands. Experiments show that artificial light at night can affect plant growth and respiration and have other physiological effects (Kwak et al. 2017, 2018). In the environment, artificial light at night affects plants primarily by impacting photoperiodism and circadian rhythms. Laboratory experiments suggest there are also effects on dark repair and recovery. Low levels of light at night can cause significant delay in leaf drop in certain tree species (Matzke 1936; Massetti 2018). Sensitivity varies greatly between species. Laboratory experiments show a wide range of responses to artificial light at night in various plant species, including delay and promotion of flowering, enhanced vegetative growth (Gaston et al. 2013), and delay of budburst (Brelsford and Robson 2018). These types of effects may occur in the environment, but further study is needed. Artificial light at night can negatively affect the growth of certain crop plants in field settings, as discussed in Schroer and Holker (2016), but these potential effects have yet to be studied in noncrop species in the environment. Many flowering plants are highly dependent on pollinators for reproduction (seed production) and genetic fitness through cross pollination. Effects of artificial light at night on pollinators also affect plants that rely on those pollinators (Altermatt and Ebert 2016; MacGregor et al. 2015; Owens and Lewis 2018) and has been demonstrated in a field study by Knop et al. (2017). Their study shows that the presence of artificial light at night reduced the number of visits to flowers by nocturnal pollinators, which resulted in a significant decline of fruit set in the plants in the study area. The decline in fruit set likely affects the availability of food to daytime pollinators. A study on horse chestnut trees exposed to artificial light at night shows that leaf size and senescence were influenced. This led to faster reproduction of horsechestnut leaf miners (insects) and increased tree damage (Schroer et al. 2019).
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