Linkages among climate, vegetation and fire in Fuego-Patagonia during the late-glacial and Holocene (Chile).

摘要

A knowledge of past fire regimes and their forcing mechanisms is of fundamental importance for modeling the role of fires in ecosystem response to future climate change. In Fuego-Patagonia, the impact of climate on late-Quaternary variability in fire activity has been an issue of ongoing debate. This dissertation explores the linkages between fire, vegetation and climate in Fuego-Patagonia during the late-glacial, the Holocene and the period of European impact by applying a multi-proxy approach (pollen, macroscopic charcoal, and peat macrofossil analyses). A contiguous decadal-scale record of peat macrofossils and macroscopic charcoal from Rio Rubens Bog (52°08'15"S 71°52'53"W), Chile, demonstrates a strong link between Holocene changes in effective moisture and fire frequency on both multi-millennial and shorter (century-to-millennial) timescales. Fires were frequent in the arid early Holocene (prior to 5.5 ka BP) and infrequent in the mesic late Holocene. Also, fires clustered in century-to-millennial scale dry intervals that are superimposed on these long-term climatic trends. Furthermore, postglacial fire histories in southern Patagonia and Tierra del Fuego show distinct geographical trends, reflecting moisture gradients. Thus, prior to European impact, fire-conducive climate appears to have been an important pre-requisite for fire occurrence in this region.; The modern fire regime at Rio Rubens was established only in the last ca. 300–400 yr. Within the context of the late Holocene, the high fire frequency since ca. AD 1600–1700 is highly unusual. The coincidence between weed introduction and frequent fires, during a wet climate interval, favors a change in human ignition frequency as the overriding factor since early European contact.; Late-glacial vegetation changes in the lowland regions of southern Patagonia and Tierra del Fuego appear to be primarily influenced by changes in precipitation rather than fire activity or temperature. Late-glacial vegetation succession at Rio Rubens Bog suggests a unidirectional increase in effective moisture, with the most significant increase at ca. 13 ka BP. A progressive moisture increase during the late-glacial interval is also registered from north to south (44 to 55°S). These spatial and temporal moisture patterns were probably associated with a poleward shift of the southern westerlies from their LGM position in three distinct phases.