Grasslands cover about one-quarter of the earth’s land surface (Ojimaet al. , 1993) and span a range of climate conditions from arid to humid. Grasslands vary greatly in their degree and intensity of management, from extensively managed rangelands and savannahs – where animal stocking rates and fire regimes are the main management variables – to intensively managed (e.g. with fertilization, irrigation, species changes) continuous pasture and hay land. Grasslands generally have vegetati on dominated by perennial grasses, and grazing is the predominant land use. Grasslands are generally distinguished from “forest” as ecosystems having a tree canopy cover of less than a certain threshold, which varies from region to region. Below-ground carbon dominates in grassland, and is mainly contained in roots and soil organic matter. The transition along rainfall or soil gradients from grassland to forest is often gradual. Many shrublands with high proportions of perennial woody biomass may be considered to be a type of grassland and countries may el ect to account for some or all of these shrublands in the grasslands category. Many grassland species have developed adaptations to cope with grazing and the common perturbation of fire and consequently both the vegetation and soil carbon are relatively resistant to moderate disturbances from grazing and fire regimes (Milchunas and Lauenroth, 1993). In many types of grassland, the presence of fire is a key factor in preventing the invasion of woody species which can significantly affect ecosystem carbon stores The 1996 Guidelines dealt only with emissions from tropical savannah burning and changes in biomass associated with conversion of grassland to other land use. Three sets of calculations were used to produce estimates of CO2 emissions due to grassland conversion: (i) carbon dioxide emitted by burning above-ground biomass, (ii) carbon dioxide released by decay of abov e-ground biomass, and (iii) carbon dioxide released from soil. No explicit provisions were made for reporting changes in the carbon stocks of grasslands associated with changes in woody perennial biomass cover or from changes in management of these systems
Année de publication
2006
Auteurs
Verchot L; Krug T; Ogle S M; Raison J; Li Y M; Martino D L; McConkey B G; Smith P; Lasco R D
Langue
English
Mots clés
environmental management, greenhouse gases
