[forester]

.... they often trade on an acre for acre basis,

Hedgetrimmer is correct, it is value for value. Timber accessed by existing roads has more value then timber with no access. From the article:

The Forest Service will give Anderson-based Sierra Pacific Industries 1,843 acres of the Eldorado National Forest, broken into 14 parcels, in exchange for 16 parcels totaling 3,394 acres, under an agreement posted this week.

In this case, the government will get almost twice as much land as it is giving up. The question to ask is, why are these trades only being done by large companies and the Nature Conservancy? Why can't small landowners intiate swaps like this?

[tertiary01]

I believe they occasionally will trade small landowners, for parcels, especially if the parcel contains a coveted habitat for study, preservation or whatever. But they usually will try to condemn it instead. In my area much of the private land originated as patents, and the gov. still acts like they believe they have ultimate ownership. My experience has only been from talking with land owners and people who work in the National Forest, not personal experience or research.