Integrating Spectral Indices and Climate Data to Monitor Ecological Changes in Protected Areas

This study develops a methodological framework combining three spectral indices—Soil Moisture Index (SMI), Leaf Area Index (LAI), and Normalized Difference Vegetation Index (NDVI)— to detect possible ecological changes in the Parangalitsa eLTER site from 2015 to 2024. The indices values are overlayed, and deviations are outlined to look for patterns. Analyzing the indices value and their ranges in conjunction with the land cover, slope inclination and aspect provides additional insight into the environmental conditions that impact the vegetation vigor and the way remote sensing vegetation monitoring can detect it. The results are then correlated with climate data, confirming that drought conditions are generally followed by lower SMI and LAI values, whereas NDVI values exhibit a delayed response. Although the relation is not always straightforward it offers insights into the interplay between ecological dynamics and climatic drivers. By integrating spectral indices with land cover, the framework identifies possible areas of ecological sensitivity, particularly in coniferous forests where overlapping deviations signal potential changes in the state, structure, and health of the vegetation cover. This holistic approach is applied on a high-valued protected area with unique biodiversity, almost no human activity, a region with diverse land cover and steep terrain where some of the most productive forests in Bulgaria thrive. The greatest deviations for territories are concentrated in territories covered with mature Norway spruce and Silver fir forests with high leaf biomass situated on northern slopes with big inclination. Although the results have not been verified by dedicated terrain observations yet, recent studies confirm that disturbances in the indicated forests are indeed registered. The framework has the potential to provide additional information for researchers and foresters in their terrain studies and help them focus their attention on problematic areas.