Late Holocene vegetation and environmental dynamics of the Araucaria forest region in Misiones Province, NE Argentina

Abstract

This paper presents the late Holocene vegetation and fire history record from Parque Provincial Cruce Caballero, Misiones, NE Argentina (26° 30′ 55.35″ S, 53° 59′ 44.73″ W). The pollen and charcoal content of the 194 cm deep sediment core dating to ca. 1840 cal yr BP permitted the recognition of three distinct zones. Zone CC -1 (before ca. 1810 cal yr BP) was characterised by a forest dominated by Myrtaceae that also included other forest taxa like Alchornea, Trema and Moraceae/Urticaceae. The presence of Zea mays (maize) pollen grains around 1840 cal yr BP suggests the presence of pre-Colombian groups in the region who practiced food-production. Zone CC -2 (ca. 1810 to ca. 40 cal yr BP) witnessed the establishment of an herbaceous wetland in the locality as evidenced by the formation of peat and the increase in wetland taxa, in particular the Cyperaceae, indicating the change to a wetter and less seasonal climate that appears to be coeval with pollen records and soil-depth profiles' carbon isotope records documented in other regions of the southern Brazilian highlands during the late Holocene. The basal section of this zone also documents the arrival of Araucaria angustifolia trees to the region, the presence of maize, and a moderate increase in fires that could be related to more intense human activity in the region. The upper section of this zone shows a slight increase in A. angustifolia paralleled by a raise of other typical elements of mixed Araucaria forests like Clethra, Ilex, Myrsine and Podocarpus. Zone CC -3 (ca. 40 cal yr BP–today) shows a major increase in trees and ferns (particularly Osmunda) at the expense of sedges and grasses evidencing a local change from a wetland dominated herbaceous vegetation to the one dominated by arboreal taxa and ferns that exists today. This zone also shows a reduction in regional fires and the disappearance of local fires that seems to be associated to the creation of the Parque Provincial Cruce Caballero. Poaceae pollen percentages remained relatively low throughout the sequence indicating that the region did not support Campos (grassland) vegetation but was a forested landscape during the late Holocene.