New estimates of organic matter reserves and net primary productivity of the North American tundra ecosystems

The reserves and fluxes of carbon in ecosystems of the circumpolar tundra biome should be among the most responsive to climatic change, including their transformation from a CO2 sink to a CO2 source with respect to the atmosphere. To estimate accurately the significance of Arctic tundra to global carbon stocks and balances, quantitative geographically referenced estimates of the masses and fluxes of carbon are needed. Although new empirically based estimates of reserves and productivity were recently obtained for the Eurasian part of the tundra biome using GIS technology, the figures currently used for carbon reserves and productivity of the North American tundra ecosystems are based on earlier expert estimates or large scale models based on data primarily for non-tundra areas. To obtain new more empirically based estimates of the reserves and fluxes of carbon in North American tundra ecosystems a set of records of North American tundra ecosystems was obtained from the Global Arctic/Alpine Climate/Soil/Plant Productivity Data Base (Global Change Research Group, San Diego State University). This data base contains phytomass, productivity, climatic and soil characteristics for nearly fifty tundra-type ecosystems studied during the past 30 years in Alaska and Northern Canada. This information was used to interpolate the necessary data for all the tundra cells (1 X 1 degree) of the simple GIS, based on the Global Vegetation Map and the FAO/UNESCO Soil Map of the World. By integrating the corresponding maps of phytomass and productivity the quantitative estimates of the reserves and. productivity fluxes of organic matter in tundra ecosystems of North America and Greenland (4.12 x 10(6) km(2) total area) were obtained: 2.26 Gt above-ground phytomass, 4.99 Gt total phytomass, 91.3 Gt soil organic matter of the active layer; 0.56 Gt/yr above-ground net primary production; 0.98 Gt/yrotal net primary production. As an alternative means of determining the productivity totals for North American tundra ecosystems, the phenomenological model of the form: NPP=f(T,H,G), relating net primary production of tundra ecosystems to climatic, soil and vegetation factors, was applied to the GIS layers of mean annual temperature (T), soil organic matter content (H), and above-ground phytomass density (G) to produce a map of modelled NPP estimates for North American tundra ecosystems. The subroutine of spatial integration of the local production estimates takes into account geographical changes in the landscape composition (proportions of the zonal, meadow, mire and aquatic ecosystem types) and results in totals of 0.58 Gt/yr for above-ground and 1.16 Gt/yr for total net primary production of tundra ecosystems of North America and Greenland.