Biofuels from a woody invader in grasslands, Mesquite (Prosopis glandulosa)

Much of the non-arable grasslands in the southern Great Plains (USA) are infested by woody plants that degrade ecosystem stability by increasing soil erosion and reducing herbaceous production and diversity. In addition, woody infestation causes economic hardships for livestock producers dependent on naturally growing forage grasses. Treating invasive woody plants will become uneconomical in the future as fossil-fuel costs increase. A potential solution is to utilize these woody invaders for cellulosic biofuel. Honey mesquite (Prosopis glandulosa) is a primary candidate because of abundant populations in the region, high potential yield (13-27 megagram/ha), reliable growth during drought without fertilizer or irrigation, and high regrowth capacity following aboveground harvest. Reducing mesquite competition with grasses after harvest will have the added effect of increasing herbaceous forage production for livestock. Moreover, harvesting in patterns that leave woody thicket patches mixed with harvested patches can facilitate wildlife habitat development. Harvest studies of different-aged mesquite regrowth found that stems > 3 cm diameter account for 40 % of total tree mass by 7 years, while leaves, twigs and smaller stems make up the remainder. Optimum re-harvest is projected at 10-12 years in north Texas but could be fewer years at more southern latitudes or higher precipitation regions. Effects of a recently developed woody plant harvester on harvest yields and impacts on soils and herbaceous vegetation will be reported. Long-term utilization of this potential biofuel source could enhance ecosystem restoration and traditional agricultural production if managed properly.