How would a drastic reduction in plant life on earth affect the atmosphere?

Plant are recyclers, they recycle everything present in air. If there is a reduction in plants on earth, there will be harmful gases accumulated all around us. Our atmosphere will be accumulated with hazardous gases releases from automobiles, factories, and chimney. The carbon dioxide will accumulate in air and the oxygen will be depleted with time and eventually survival on earth would not be possible.

Moro ever, Lives of animals and birds would be affected badly if there well less plants on earth because plants are their main food source and habitat.

you did not attach the discourse, but i assume it to be the discourse on the origin and basis of inequality among men (the original titile in french is: "discours sur l'origine et les fondements de l'inégalité parmi les hommes"), also know as "second discourse". in this discourse, jean-jacques rousseau emphasizes that private property is the basis of all inequalities.

therefore, what enabled the old regime to maintain as long as it did was private property.

the answer to your question is tooth decay.