The Structure and Function of Ten Western North American Grasslands: IV. Compartmental Transfers and Energy Flow Within the Ecosystem

Abstract

Seasonal and daily rates of inputs to and outputs from the various primary producer compartments of 10 North American grassland sites are presented. Net accumulation rates of total net primary production (TNP) ranged from approximately 1 g m-2 day-1 in the desert grassland to over 11 g m-2 day-1 in the mountain grassland. The average net accumulation rate of TNP was 4.4 g m-2 day-1 for ungrazed grasslands, and slightly more for the grazed grasslands. A significant amount of the variability in mean daily accumulation rates of TNP for ungrazed grasslands was related by regression analysis to variations in long-term mean annual temperature and long-term mean annual precipitation. Above-ground net primary production (ANP), variations in annual precipitation, and the amount of live material transferred during the growing season to the standing dead compartment are discussed. The percentage of incident solar energy captured in the ungrazed and grazed grasslands is given. The lowest values for efficiency of energy capture were recorded for the semi-arid grasslands of India and the North American desert grassland. Water-use efficiency was highest in intermediate rainfall regimes, such as the sub-humid grasslands of India and the shortgrass and mixed-grass prairies of North America. Water-use efficiency declined in the humid Indian grasslands and the North American tallgrass prairie, and in the more arid grasslands.