Tree has a wide variety of filtering functions.
Trees living in metropolitan area often found themselves living right beside roads. What they probably don’t know is that they are under a never-stop mission of filtering dust, car exhaust and noise for every citizen.
Trees living in mountain area seemingly have no particular mission at all — Yes and no. They normally have no necessity of doing the nasty work their urban sister/brothers doing all day, but they do have the risk of being knocked down completely to warm a living room or to make a good pizza.
Apart from praying day and night, mountain trees also filter things. The difference here is that they only filter things they would like to filter.
Bird, for example.
Hooded crow, to be specific.
A piece of meadow, divided by a line of trees in the middle, if there’s a group of hooded crow foraging on one side of the tree line, if they suddenly take off due to the unexpected appearance of a bergamasco dog, if they all fly to the other side of the meadow, merely one in ten could make it.