Estimating Aboveground Net Primary Production in Grasslands: A Comparison of Nondestructive Methods

Aboveground net primary production (ANPP) is an important ecosystem property that is affected by environmental variability. ANPP in grasslands is typically measured by clipping peak live plant material. However, this method is time intensive (and therefore expensive), making it difficult to capture spatial and temporal variability. Additionally, it is impractical to use a destructive method to estimate ANPP in long-term, permanent plots. Thus, many double-sampling techniques have been developed to reduce costs and increase sample size. The objective of our study was to assess the accuracy and precision of nondestructive techniques to estimate ANPP as supplements to the traditional method of peak biomass harvest at two grassland sites. We harvested biomass and compared estimates from the same plots to 1) canopy interception using a point frame, 2) green cover estimates derived from a digital camera, and 3) reflectance measurements using a handheld radiometer. We calculated the optimum allocation of sampling effort to direct and indirect methods to minimize sampling cost yet achieve a desired precision. We found that the point frame technique explained the highest proportion of the variability in biomass at both sites (R(2) = 0.91, 0.90). However, our cost-optimization analysis revealed that the radiometer technique, although less accurate (R(2) = 0.38, 0.51), could achieve a desired precision for lower labor costs than the point frame. The radiometer and point frame methods will be a useful tool for grassland ecologists and rangeland managers who desire fast, nondestructive estimates of ANPP.