Why do we burn brushpiles after we cut buckthorn and other invasive plants? There are several good reasons.
- It's really fun.
- Brushpiles are an eyesore, and burning allows us to dispose of them without running noisy wood chippers (also, we'd still have to dispose of the chips somehow).
- Decaying buckthorn changes the chemistry of the soil on the forest floor.
I think (1) and (2) above are self-evident, but let's look at (3) for a moment. It turns out that buckthorn litter decomposes faster than native plant litter, and that this decomposition increases the carbon and nitrogen levels in the soil. Now, farmers and backyard gardeners know that nitrogen compounds are important for plant growth, so one might think that the binding of additional nitrogen in the soil would help plant growth. However, it seems that in Chicago-area woodlands, the additional nitrogen and other changes in soil chemistry actually prevent native plants from colonizing the area, effectively favoring the growth of nothing but more buckthorn. Yikes! I've also heard that buckthorn contains a toxin that prevents other plants from growing nearby (this phenomenon is called allelopathy), but I haven't been able to find a literature reference for this.So, to prevent brushpiles from becoming eyesores, to keep excess nitrogen out of the soil, and to enjoy the crackling of the fire during our workday breaks, we burn brushpiles.
Heneghan et al. (2006). "The invasive shrub European buckthorn (Rhamnus cathartica, L.) alters soil properties in Midwestern U.S. woodlands." Applied Soil Ecology 32:142–148.