The effect of a prescribed fire on nutrient concentration and standing crop of understory vegetation in ponderosa pine.

Understory vegetation from sawtimber, pole, and sapling strata was sampled for biomass and nutrient concentrations, the summer following a fall-prescribed fire in ponderosa pine Pinus ponderosa on basalt soils in Arizona. Nutrient concentrations were generally higher on burned than unburned plots, with striking differences among overstory strata. K showed the most consistent response, while N showed the greatest increase in magnitude. The greatest increases in nutrients were in the sawtimber stratum, where Festuca arizonica and the miscellaneous grasses category were at times twice as high in N concentration on the burned sites. Differences in understory biomass were most obvious in September when both pole and sapling strata were twice as high on burned plots as controls. Responses varied highly depending on species, overstory type, and season, but in general this prescribed fire appears to have increased nutrient availability, stimulating understory production and increasing nutrient concentration thus improving forage quality for both livestock and wildlife. -from Authors