Effects of Light Pollution on Urban Tree Phenology

The research done serves a purpose as cities continue to grow in population causing negative effects in the surrounding environments. This article studied if the intensity of light pollution effects tree phenology in urban environments. There has been far less recorded research measuring light pollution intensity on tree phenology. Nevertheless, worldwide artificial light has been promptly increasing by 2.2% every year. In previous studies, researchers have found that trees growing near artificial light have a delayed reaction to autumn, this often causes their leaves to freeze fully green which ultimately causes breaking branches.

Figure 2 shows the effect of light pollution on leaf color change and leaf falling rates in staghorn sumac and sycamore maple trees, ranging in age from 10 to 80 years. These trees were studied in three different locations in Slovakia, each with varying light pollution levels. The first site was a newer housing estate with modern lighting, the second was an older estate with less efficient lighting, and the third was the town center. Light pollution intensity was measured under both cloudy and clear skies. The study found that light pollution significantly delayed the phenological processes in trees. As shown in Table 3, site 3 (the town center) had the highest light pollution levels. This is reflected in Figure 2, where the tree in photo A (from site 3) shows a delayed phenological change compared to the tree in photo B (from site 1).

Figure 3 analyzes light pollution of three sites in Slovakia from 2013-2016 under different weather conditions, using GIS to measure light in lux. Cloudy skies increase pollution levels, with the Town Centre at 8.5 lux in 2015, while Tepličky showed the least pollution, increasing from 1.1 lux in 2013 to 4.8 lux in 2016 under clear skies. Zlatý Potok had higher averages, 7.8 lux under cloudy versus 5.7 lux under clear skies. This shows that light pollution delays leaf fall by showing phenophase timing differences between lit and dark tree sections.

Figure 4 shows the timing and duration of leaf coloring (LC) and leaf fall (LF) for sycamore maple and staghorn sumac in Slovakia from 2013 to 2015, comparing trees in artificially lit urban areas and darker control areas. Artificial lighting caused a 15-day delay in leaf coloring for staghorn sumac in lit areas, starting on October 10, versus September 25 for unlit trees, and extended the leaf coloring phase by about 30% and leaf fall by 20%. These results demonstrate how artificial lighting disrupts natural seasonal cycles, underscoring the ecological impacts of light pollution on urban tree phenology.

The study confirmed that light pollution delays tree phenological phases, as trees in brighter areas experienced longer leaf coloring and falling times. The figures prove that light pollution impacts the phenological process of trees, causing them to be significantly delayed. Stronger effects were seen in higher light intensities areas and under cloudier skies. These findings lay the groundwork for future research to explore strategies for reducing light pollution. Additionally, this opens avenues for studying the broader ecological effects of light exposure on urban flora and fauna, guiding more sustainable city planning.

Skvareninová, J., Tuhárska, M., Skvarenina, J., Babálová, D., Slobodníková, L., Slobodník B.,

Středová, H., & Minďaš, J. (2017). Effects of light pollution on tree phenology in the urban environment. Moravian geographical reports. 25(4), 282-290. 10.1515/mgr-2017-0024.