This data set contains two ASCII text files; one providing above-ground biomass, productivity, and bioelement concentration data for a derived savanna at Cañas (10.4 N 85.1 W Elevation 45 m) in northwestern Costa Rica, and the other providing climate data from the La Pacifica weather station near Cañas and rom other sources. Monthly dynamics of above-ground plant matter were monitored from July 1969 to June 1970 using harvest procedures within an exclosure to restrict grazing. The climate data are available from three time periods: 1951-1960, 1963, and 1969-1970. The climate is characterized by a dry season from late November to April, with little seasonal differences in temperature. The Cañas study site is dominated almost exclusively by Hyparrhenia rufa, a perennial grass of African origin introduced extensively throughout the tropics. The original vegetation cover was closed semideciduous forest. The study area was deforested and converted to a grass savanna around January 1947, 22.5 years before the start of the present study. Light grazing by cattle and horses is accompanied by burning of the Cañas savanna annually between December and April. Above-ground net primary productivity (ANPP) was estimated by two methods: maximum standing crop of herbaceous shoot tissue (peak live + dead matter) (968 g/m2/year); and the sum of monthly estimates of shoot production (including estimated mortality) (1,387 g/m2/year). End-of-season (November, 1969) live root biomass estimates of 1,220 g/m2 at 0-20 cm depth and 2,254 g/m2 at 0-100 cm depth are available in the literature.