“Helping nature” to make things move faster is a normal thing there. Other examples are reintroducing wolves in Yellowstone, and sinking old ships to help reefs develop. Would you be opposed to those, too?
> In densely populated areas, there is no nature; everything that happens or doesn’t happen gets decided by man.
Nonsense, and besides the point. In the densest of cities there is plenty of nature (beside us). And in any case this planned forest isn't being planted through the middle of manchester and leeds.
Even then, if an acre of urban land is left idle by man it will sprout all manner of weeds and, not before long, trees. Many a distopian sci-fi film will show this.