Most of the tree loss that occurred in North America happened nearly two hundred years ago, when settlers were cutting down the vast deciduous forests east of the Mississippi River. It turned out much of this land wasn't great for farming and has been allowed to return to forest.
East of the Mississippi River, any land which isn't plowed regularly or paved over will return to forest all by itself. You can see this happening in fallow fields where volunteer saplings have grown up. Left alone, pastures will become forests once more and many of them have done exactly this.
In the study that the article cites, the U.S. is compared with Canada, Russia, China, Brazil, Indonesia, and the (sic) Democratic Republic of the Congo. This comparison makes little sense as the last three are home to vast tropical rain forests and the first two are home to enormous boreal forests. The U.S. has little of either, outside of Alaska, and never did.
