Grass páramo as hunter-gatherer landscape

Abstract

Tussock grass páramo constitutes the dominant vegetation of the high tropical Andes and cordilleras of Costa Rica. Its distribution, composition and the location of the upper forest line are ascribed, by broad consensus, to climate. The zonal argument finds support in the altitudinal movements of páramo during the Pleistocene, clearly responding to changes in precipitation and temperature. I ask here, however, if the principal ecological variables driving post-Pleistocene páramos are circumscribed solely by climate. The combined pollen, charcoal and archaeological evidence generated in recent decades suggests a distinct Holocene etiology. Five principal conclusions emerge: (1) the sedimentary charcoal record establishes that grass páramo is a fired landscape, (2) natural sources of fire, specifically volcanoes and lightning, are incapable of generating the fire regime apparent in the sedimentary charcoal record, (3) burning at most sites intensified significantly between 13,000 and 11,000 cal. yr BP, and maintained heightened levels during the Holocene, (4) archaeological findings suggest that the original settlement of the Andes coincided with the sedimentary charcoal rise, and (5) the subsistence logic of hunter-gatherers argues strongly for firing the vegetation to increase resource productivity and reliability. From the pioneering mixed vegetation after deglaciation, anthropic fire selected in favor of tussocks and against woody species, generating a novel plant association. I propose, therefore, that Holocene grass páramo is not zonal vegetation, but rather a hunter-gatherer landscape.