The phrase "different vegetation" refers to a variety of plants or plant life found in a particular area, which can be distinguished from other places by the types, shapes, and sizes of plants growing there. Full definition
Change in Amazon greenness from 2000 to 2012, measured as Normalized Difference Vegetation Index (NDVI). (sciencedaily.com)
To track the greening of leaves, the researchers relied on the Normalized Difference Vegetation Index data acquired by the Moderate Resolution Imaging Spectroradiometer on board NASA's Terra and Aqua satellites. (sciencedaily.com)
The line reflects the Normalised Difference Vegetation Index (NDVI): the higher the value, the more vegetation is thriving in the area. (sciencedaily.com)