Question

what is natural vegetation

Answer 1

Natural vegetation means any plants or trees that grow on their own ‘naturally’ without any form of human intervention. 
Certain type of plants of trees have a natural place of origin or habitat, and before humans began to harvest vegetation and  cut down trees , this type of vegetation would grow naturally without any form of man-made chemicals such as pesticide, to manipulate its growth.
Each  place on earth  had a community of plants that were natural and adapted to a specific area, and, more importantly, had grown accustomed to that climate zone. 
It is this type of plant community that is referred to as "natural vegetation”. 

Answer 2

Natural Vegetation refers to a plant community which has grown naturally without human aid and has been left undisturbed by humans for a long time.