This makes me wonder how much damage has been done to North America, which has lost almost all of its megafauna to humans. Horses, bison, wolves, grizzlies, etc. are confined to small areas. The mastodons and ground sloths are long gone. (They were so delicious.) We've seen that reintroducing even one keystone species like wolves can have tremendous effects. Occasionally, humans manage to replace a missing piece. How is a lawnmower like a bison? It cuts the grass so birds can forage for seeds and bugs, although regrettably it provides no other benefits such as fertilizer, meat, or buffalo robes. Ghost trees still make fruit and thorns for mammoths and ground sloths. It's the shifting baseline problem; we have a hard time seeing what isn't there.
Learn to look for the missing pieces. And observe what's there while we still have it.