The rainforest is many times more efficient at producing O2, and trapping CO2, that is why it matters so much globally. Forests in colder climates do more to help the local air and water quality, and biodiversity, but their loss or gain is not directly critical to human life.

Specifically in the US, there seem to be reforestation programmes, but it depends a lot on the state. This interactive map shows the last 20 years. This is after some major reforestation that started at the beginning of the XX century, in Europe for example. There are still large reforestation efforts going on, but also a lot of commercial logging that keeps tree cover gains at a net zero, or close to it.

Edit: a word.