It does, i forget where in the middle east, some enemy baracaded themselves behind walls of marijuana plants, we could not run through them, or see through them with infrared because the heat signature was to strong it shielded what ever was behind it. Im not sure how exactly it works amongst plants but it does happen. now how much u need to activate this, i would assume a shit load. you would need dense amounts of plants and massive trees of plants. its not that it doesnt happen with other plants, its just they need to grow close together and bushy/dense. anything will retain heat at that point.