Analysis of spatio-temporal variation and driving forces of leaf area index in Hainan Island over the last 20 years based on MODIS data

Leaf area index (LAI) is a critical indicator of vegetation structure, essential for monitoring vegetation growth, assessing ecosystem health, and guiding environmental protection strategies. Hainan Island, renowned for its unique geography and climate, experiences significant impacts from climate change and human activities, influencing its abundant vegetation resources. Therefore, understanding the spatio-temporal dynamics of LAI on Hainan Island is crucial. Using the MOD15A2 LAI product dataset and meteorological data from 2002 to 2022, we employed Theil-Sen median analysis and Mann-Kendall trend tests to analyze LAI trends and assess climatic influences. We found that: 1) From 2002 to 2022, LAI has generally increased across Hainan Island, with a more pronounced trend in the northern regions compared to the south. This trend correlates with the expansion of the rubber industry in the north and the development of tourism in the south, highlighting the significant impact of human activities on LAI. Additionally, LAI tends to be higher in central areas and lower in peripheral regions, consistent with spatial variation of topography. 2) The average coefficient of variation (CV) for LAI over the last 20 years was 0.136, indicating minimal fluctuations in vegetation dynamics and ecological stability of the island. 3) Under the background of a warming and drying climate, we observed a saturation effect in vegetation growth response to increasing temperatures: LAI in most northern regions positively correlates with increasing temperature, while most southern regions show a negative correlation. Precipitation exhibits opposite effects, influencing temperature gradients. These results underscore the complex interplay of climate, topography, and human activities as primary drivers of spatial and temporal variations in LAI on Hainan Island. This study provides a scientific foundation for enhancing vegetation protection, promoting ecological restoration, and implementing climate-resilient management strategies across the island.