Artificial light at night is now recognized as a major environmental pressure — it disorients migratory birds and sea turtle hatchlings, shifts pollinator interactions, and reshapes entire nocturnal food webs. But protected areas, where human activities are supposed to be restrained, are rarely monitored for light itself.
A decade of darkness, measured from orbit
Researchers led by Fangzheng Liu of the Chinese Research Academy of Environmental Sciences used nighttime-light records from the Joint Polar Satellite System (2015–2024) to build a time-series dataset for the Beijing-Tianjin-Hebei region, computed mean ALAN radiance for every nature reserve and functional zone, ran Mann-Kendall trend tests, and classified reserves into disturbance grades with landscape-pattern analysis of lit patches.
Two findings frame the story. First, conservation works: reserves together hold only about one quarter of the region's average ALAN radiance, confirming that protection measures keep light down. Second, effectiveness is eroding: 94.54% of the area inside reserves shows a significant or extremely significant brightening trend. 22 reserves climbed one disturbance grade over the decade and 12 climbed two. Low- and moderate-disturbance patches now spread both inside reserves and along their edges, while high-disturbance patches concentrate at reserve peripheries — the classic signature of surrounding urban growth pressing inward.
The species-specific signal matters most for wetlands: wetland reserves showed significantly higher ALAN radiance than all other reserve types, and core and buffer zones differed significantly from experimental zones — evidence that functional zoning does shape light exposure, though not yet enough.
"We often think of light pollution as a city problem, which has little to do with protected areas" the corresponding author said. "But night is itself a habitat — for night herons, for insects, for anything that hunts or hides in the dark. Our maps show that within protected areas, darkness is being lost almost everywhere. The encouraging part is that light is one of the most controllable pressures, as long as management agencies and local communities take action".
Why it matters
Light is unusual among environmental threats: it is reversible within minutes of switching a lamp off. The authors call for stronger monitoring and regulation of human activities around protected areas, and for nighttime-light remote sensing to become a routine tool in protected area planning, supervision of key ecological spaces, and conservation effectiveness evaluation — the same way land use and land cover change is monitored today. The authors propose the method as a tool for wider application in protected-area assessment.
· Citation: Pan YH, Ma BR, Du LS, Zhu YP, Fang XW, Liu FZ (2026) Characteristics of artificial light at night disturbance in the Beijing-Tianjin-Hebei region and its nature reserves. Biodiversity Science, 34(8): 26245. DOI: 10.17520/biods.2026245 (open access).
· Article link: https://www.biodiversity-science.net/CN/abstract/abstract104087.shtml
· Images available: nighttime-light maps of the region and reserves, disturbance-grade maps (to be supplied and rights-cleared by the authors or journal). Visually strong — suitable as lead image.
· The paper is already published; this release carries no embargo.
