Granite Geek: Satellite Images of Forests Don't Tell the Whole Story

Jun 23, 2015

Mapping New Hampshire’s forests is tricky business. There’s a lot of land to map, and the satellite images that scientists use to augment data from other sources have significant limitations. Nashua Telegraph columnist and writer at Granitegeek.org David Brooks caught up with a few UNH researchers trying to track how human behavior has changed the forests. He spoke with NHPR's Peter Biello.

What are these images good at showing us?

They’re good at showing the big picture. It’s funny, because when I started satellite imagery was really hard to see. You had to buy it for huge amounts of money. And now it’s everywhere, and we’ve gotten kind of used to it with Google Earth. For example, this is talking about forest cover. This is a great way to get a large-scale view of what has happened in all of Coos or Hillsborough County, for that matter, in ways that would have been impossible otherwise. In the old days, when you had people hiking around on mules or even flying on airplanes and taking laborious pictures, you never really had the big picture. It’s used for obviously tons of things. One area that’s particularly interesting is using satellite data to figure out snow pack.

And what are these images not very good at capturing?

The close up. One of the quotes, as you might have seen in the column, from Mark Ducey, a Professor of Forest Biometrics (which is a great title, by the way) at UNH—he talked about how you could have a pixel-toggle between forest and non-forest. In other words, a single pixel on the screen, which could encompass many acres. The satellite passes over and indicates whether it’s forested or not forested, but that could hide a lot of detail, and of course the devil is in the details. And what Ducey and his colleagues are trying to do is use other data, specifically census data, which is not at all obvious, to do a better census of what is happening in New Hampshire’s forest and other forests on a small scale, using satellite data.

One of the things you wrote about in the column is that vacation homes don’t often show up on these maps because they might be in wooded areas and they might look like just a patch of forest, but that home could have very different implications from an environmental stand-point and a forest-use standpoint.

And from an economic standpoint as well. Economically, for example, if you were doing economic planning, you could say, here’s X amount of forest that could be harvested every 20 years, and that’ll bring in X number of dollars, so we’ll factor that into our long-term calculations, but if in fact half of that forest is second homes, they’re not going to be logging that property, they’re not going to be adding products to the forest industry. And you need to know that to factor that in. Easier said than done, but that’s where census data can help.

What would a complete map of NH’s forests help the state or environmentalists or other interested parties?

Economic planning is a big deal. If you have a better sense of what’s going on in the wooded areas, the vacation areas, the developed, the formerly-developed, the about-to-be-developed areas of the state, you can do better economic planning. Environmental is a big deal. If you want to talk about wildlife, one of the big things is keeping wildlife corridors open, so that animals can move from one part of the state to the other. That’s important as the climate changes because this could help plan that. And the carbon balance—there are some people who hypothesize that the northeastern forests are in general no longer our carbon sink because they are so mature, so if people are saying, “Well, we can burn X amount of fossil fuel because part of it will be taken up by the northeastern forests, but the northeastern forests aren’t taking up that carbon, we need to know that.