Sentence:  As towns continue to grow, replanting <WSD>vegetation</WSD> has become a form of urban utopia and green roofs are spreading fast. Last year 1m square metres of plant-covered roofing was built in France, as much as in the US, and 10 times more than in Germany, the pioneer in this field. In Paris 22 hectares of roof have been planted, out of a potential total of 80 hectares. 
Meaning of the word marked with <WSD> tags:  Plants, taken collectively.