Dynamic change in quarterly FVC of urban parks based on multi-spectral UAV images: A case study of people’s park and harmony park in Xinxiang, China

Abstract Season is a typical growth cycle unit for vegetation, revealing the spatial distribution and spatial-temporal dynamic changes of fractional vegetation cover (FVC) in parks. This information can provide a scientific basis for optimizing the allocation of park vegetation. This work focuses on People’s Park and Harmony Park in Xinxiang, China, using quarters as the temporal framework and multi-spectral high-resolution unmanned aerial vehicle images as the data source to systematically assess the spatial distribution and spatial-temporal dynamics of FVC. The findings indicated that (1) the annual FVC was primarily characterized by bare and middle areas. Spatially, the FVC in both parks exhibited a pattern of higher values along the periphery and lower values toward the center. In summer, it featured bare and highest areas, while in winter, the park was mainly characterized by bare and lowest areas. The ratios of areas at major FVC grades were significantly larger than those at other grades. In spring and autumn, the ratio of bare areas was notably high, while the distribution of areas at other FVC grades was relatively balanced; (2) the trends of quarterly FVC mean at regional scale resembled a “∩”-shaped pattern, peaking in summer, followed by spring, autumn, and winter. The bare and highest areas fluctuated the most, with their rates of change showing inverse trends. Areas at other FVC grades remained comparatively stable; (3) in the dynamic changes of FVC at pixel scale, the areas with the greatest proportions of improvement and degradation are during the summer-autumn and winter-spring periods. During summer-autumn, basically unchanged and moderately degraded areas prevailed, whereas in winter-spring, basically unchanged and significantly improved areas were more common. The FVC changes at pixel scale vary by season. Overall, the improvement and degradation areas are mainly located on the periphery of the park, internal roads, and areas with less foot traffic, while the basically unchanged areas are concentrated in the hard and water parts; (4) the spatial evolution of FVC within the parks showed positive trends from spring to summer and winter to spring, while primarily negative trends were observed from summer to autumn and autumn to winter. Multiple evolutionary paths were present in each phase, with cross-level transitions being frequent. In the construction of urban parks, efforts should be made to consciously increase the proportion of vegetation in the park’s land types, while meeting functional requirements such as use and viewing. Simultaneously, vegetation planning should be strengthened, including spatial distribution planning, vegetation structure design, and plant selection.