Sanichips are made from aspen. I'm not sure on the sustainability of aspen harvest worldwide. Aspen is one of the few hardwoods that regenerates quickly enough to be competitive with yellow pine culture, so it would seem it is at least potentially sustainable (timberland with slow-growing trees, like oak, hickory, tulip poplar, maple, etc., is often replanted in yellow pine monoculture after harvest, which has negative effects on wildlife, hydrology, etc.).
*EDIT* I didn't realize there were both aspen and "regular" sanichips. The regular sanichips are made from various hardwoods. If they were just made from waste wood from lumber manufacture, that would be fine, but the manufacturer's website indicates they are made from "selected hardwoods". Possibly they are using small trees from clear-cut operations, or even slash. I would avoid them and stick to the coco products for peace of mind.
*EDIT* I didn't realize there were both aspen and "regular" sanichips. The regular sanichips are made from various hardwoods. If they were just made from waste wood from lumber manufacture, that would be fine, but the manufacturer's website indicates they are made from "selected hardwoods". Possibly they are using small trees from clear-cut operations, or even slash. I would avoid them and stick to the coco products for peace of mind.