Hardwoods are used for a lot of things like flooring, regular boards, firewood (it burns hot) and so on. Of course when we use these woods we are cutting down the trees. Now before you go thinking "tree killers" you must understand that young trees produce a lot more oxygen then old trees, so in a way it is good to remove some of the older ones. (not all, but some) Removing a few also helps keep the forrest from over crowding.
However, when we cut down trees and send them all over the place to be made into various things there is always a risk of spreading disease. I am talking about all the little bugs that kill trees off. For example, the Emerald Ash Borer came to America not to long age in a crate that was not dried to prevent against spreading tree disease. As a result all the Ash trees starting from Indiana (I think it was Indiana) and going out from there are dieing off. This also happened in America with Chestnut Trees. When a disease spreads in trees like this it is called a blight.
So Negative Impact = Using hardwood causes tree disease to spread.
Positive Impact = Young trees produce more Oxygen then old ones
There are a lot more, but that is a good start.
