My source is a western office of the USFS. Thinking about it, it seems reasonable. Our woods out here can get really dry, I suspect much more so than the typical eastern hardwood forest.

A few years ago i went for a day hike in the local mountains and noticed that everything was powder dry. I thought "This is my last hike until it rains". Two days later, a ricochet from a group target shooting just off the highway started a 21,000 acre conflagration. I have worried about doing the same, digging with hand tools in a dry grassland.