Patchiness of above-ground vegetation, such as that in semi-arid grasslands and shrublands, can pose problems in sampling plant cover, biomass and productivity. We present a method of measuring above-ground plant biomass and production that can be applied consistently among vegetation types and that generates seasonal, spatially-explicit results. Results from 15 sites within the Jornada Basin (Chihuahuan Desert, New Mexico, USA) confirm considerable patchiness and non-normal distributions of plant biomass, even in grasslands. However, tests of adequacy of sample size and of sample error associated with the regression-based estimates of biomass confirmed that the estimates of above-ground net primary productivity are sufficiently precise to be useful in comparisons of both shrub-dominated and grassland sites.