What positive effects do humans have on the environment?

-We are the only creatures on earth that are conscious and deliberate about our impact on the environment.
-We do controlled burns to promote healthy forests.
-We are selective with our logging and replant trees we take.
-We cultivate native plants, especially those that are beneficial to multiple creatures, not just ourselves.
-We provide a predatory balance to prey populations.
-We treat our prey with compassion, something no other predator does.
-We establish more mutually beneficial relationships with animals than any creature.
-We make a concentrated effort to clean up and restore an ecosystem that has been adversely impacted by a disaster, be it manmade or natural.
-We take responsibility for the actions of our entire species, not just ourselves as individuals--something else no other creature does (you don't see rabbits having globally cooperative meetings about how they've invaded and damaged the Australian biome).
-We have compassion on other predators who would normally be our competitors, and make an effort to aid them when they are sick or injured, especially by our own actions.

In finding more effective and efficient ways to accomplish the above, we do make mistakes more often than we are successful. But we try. No other creature does that. If an animal's world crashes down around it, the best it can do is escape. But we can rebuild. We are not helpless. We are stewards.

Not a single thing positive to date, we humans are not as smart as we think, by the time man comes to see his errors it will likely be too late.
We have been warned though, in spite, man is a party animal and won't miss the water till the well runs dry.

Global warming. Ask our Secretary of State who says that melting the ice pack in the Arctic is good because it opens up lots on new areas for mineral and oil exploration.

We redistribute potassium and phosphorus inland, and we're better at it than migrating salmon or seabirds.

We removed much of the continuous forest that covered the eastern portion of what is now the USA. Large blocs of forest are biological desert. Ask any birder or field biologist. Most of the wildlife is found around the ecotone (where one habitat abuts another one).