Abstract: The rapid development of cities increases urban heat island (UHI) effect. Urban greening can alleviate the heat island effect, but plant phenology could be affected by the heat island effect. Using remote sensing images, we compared the plant phenology between UHI areas and non-UHI areas as well as the different levels of UHI intensity in Beijing. Landsat-8 images for Beijing were used to invert the land surface temperature (LST). Spatial analysis methods were used to identify UHI zones and the UHI intensity classification. With data of normalized differential vegetation index (NDVI) of MOD13A1, three phenological parameters (start of growth season (SOG), end of growth season (EOG), and length of growth season (LOG)) were extracted by the Dallimer mean value method and dynamic threshold method. The three parameters were used to examine the differences in plant phenology between the UHI areas and the non-UHI areas and between different UHI intensity levels. The UHI effect of Beijing in summer was more obvious than that in winter. The SOG in the UHI areas extracted by Dallimer mean value method was four days earlier, the EOG was nine days later, and the LOG was 13 days longer than that in non-UHI areas. The SOG in UHI areas extracted by dynamic threshold method was 10 days earlier, the EOG was four days later, and the LOG was 14 days longer than that in nonUHI areas. Compared with the Dallimer mean value method, the phenology calculated by the dynamic threshold method was closer to the observation data. Under higher UHI intensity, the SOG would be earlier, the EOG would be later, and the LOG would be longer. This study enriches the response mechanism of plant phenology to the UHI effect in North China, which helps us to understand the effects of global warming on ecosystems.

Key words: heat island effect, plant phenology, NDVI, Beijing, dynamic threshold method.