干旱区生态环境知识资源中心

Fires are common in grassland regions of the world, and the frequency and severity of fire is linked to climate-driven changes in fuel loads. Western Mongolia is dominated by grasslands but the fire history of this region is largely unknown. We reconstructed modern fire (48 lakes) and historical fires (98 lakes) using sediment charcoal. Modern fuel loads were estimated using a combination of clipped plots, satellite-based estimates of annual aboveground net primary productivity (NPP) and NPP modeled from annual temperature and precipitation. Loss-on-ignition and environmental magnetics of lake sediments were analyzed as proxies for climate. We found little evidence for modern or historical fire in the landscape, as charcoal was absent from the surface sediments of 34 of 48 lakes. Charcoal influxes were uniformly low, averaging from 0.002 to 0.028 mm(2)/cm(2) per yr, over the past 1200 years at nine lakes, and the past 6000-5000 years at two of the lakes with longer sediment records. In the modern landscape, livestock grazing has eliminated most of the fuels necessary to carry a fire, as measured fuel loads (27.3+/-4.9 g/m(2)) were only similar to 20% of aboveground annual NPP estimated using MODIS Imagery or modeled from climate data. The historical absence of fire may indicate a longer history of intensive grazing than sometimes assumed, and cultural prohibitions against burning may also play a role. Regional summary indicated a >50% decrease in charcoal influxes since AD 1600 at most sites which may be related to lower temperatures or greater aridity during the ’Little Ice Age’. Alternatively this decrease in charcoal influxes may reflect increases in livestock numbers or increased local concentrations because of restrictions on the movement of animals coincident with the establishment of Manchu rule in the late seventeenth century.