Elevation-Dependent NDVI Dynamics in Arevik National Park (Syunik Province, Armenia): a 40-Year Spatio-Temporal Analysis (1985–2025)

Abstract

Mountain ecosystems are highly sensitive to climate change due to pronounced environmental gradients and strong climatic variability. Understanding vegetation responses to ongoing warming is therefore essential for assessing ecosystem resilience and developing effective conservation strategies. This study investigates long-term vegetation dynamics and their relationship with climatic warming in Arevik National Park, located in the Syunik Province of southern Armenia. The analysis was conducted using Normalized Difference Vegetation Index (NDVI) data derived from Landsat 5 TM, 7 ETM+, 8 OLI, and 9 OLI-2 imagery for the period 1985–2025 at five-year intervals. Elevation data derived from a Digital Elevation Model (DEM) and August minimum and maximum temperature data obtained from the WorldClim database were integrated within a GIS environment to evaluate elevation-dependent vegetation responses. August was selected because it represents the driest period in the study area, minimizing the influence of seasonal precipitation variability and providing more reliable NDVI-based assessments of forest vegetation dynamics. The results revealed a clear warming trend across the study area, with both minimum and maximum August temperatures showing a gradual increase during the study period. NDVI analysis indicated an overall decline in vegetation greenness and productivity, although significant spatial heterogeneity was observed. Elevation-based analysis demonstrated contrasting vegetation responses along the altitudinal gradient. Negative NDVI trends were identified in elevation zones between 450 and 2400 m a.s.l., where vegetation greenness declined by up to 16.05%. In contrast, positive NDVI trends were recorded above 2400 m a.s.l., with the strongest increase (+25.77%) observed in the 2800–3200 m elevation range. Spatial change-detection analysis further confirmed the coexistence of areas exhibiting vegetation decline and vegetation expansion throughout the study area. The findings indicate that vegetation dynamics in Arevik National Park are strongly elevation-dependent and suggest that ongoing climatic warming affects mountain ecosystems differently across altitude zones. The integration of remote sensing, GIS analysis, and climatic datasets provides valuable insights into climate–vegetation relationships in the South Caucasus and supports evidence-based conservation and management of protected mountain landscapes under changing climatic conditions.