Vegetation greening trends in different land use types: natural variability versus human-induced impacts in Greece

Vegetation greening and browning patterns in two diverse land use environments, i.e., urban areas and sites protected by environmental legislation over Greece, are evaluated and presented in this work. Urban sites correspond to areas of high man intervention, whereas the protected sites are considered as areas with least human impact and are therefore representative of the natural variability of vegetation attributed mainly to climate. Analysis of time series data in the form of least square line fitting was conducted using remotely sensed Normalized Difference Vegetation Index (NDVI) of the Moderate Resolution Imaging Spectroradiometer (MODIS) and the spatio-temporal vegetation trends were examined in the two diverse land use categories. Results showed that 99% of protected sites and 95% of urban sites exhibited significant browning or greening trends (p < 0.01) with greening patterns dominating in most parts of the country during all seasons. Regarding the magnitude of detected trends, protected areas demonstrated a higher greening trend both annually and seasonally. Average magnitudes of NDVI on an annual basis were computed to 2.04 × 10−3 year−1 for urban areas and 4.50 × 10−3 year−1, respectively. Higher rates of NDVI increase were detected in autumn and winter. Spatially, NDVI changes in protected sites demonstrated higher increasing trends by increasing latitude, whereas no major trend in the rate of NDVI change is evident on the east–west direction. Possible causal factors of those increasing NDVI trends, both climatic and human induced are discussed. Furthermore, the role of economic crisis during the last decade has been highlighted, which caused a dramatic drop in urban expansion all over the country, seems to have positively impacted vegetation productivity in those areas as well.