Holocene environments reconstructed from plant macrofossils in stream deposits from southeastern Nebraska, USA

Abstract

Plant macrofossils from sediments exposed in cutbanks of small streams on the Great Plains yield details of the history of the vegetation and climate, and potentially of the hydrologic behaviour of the streams during the past 9000 radiocarbon years. Five zones are recognized by visual inspection. Macrofossils in zone 1( c. 9000 to c. 8500 BP) indicate that upland deciduous forest was sparsely present, but that prairie, weedy and wetland habitats were also well established. Zone 2 ( c. 8500 to c. 5800 BP) is sparsely represented, but upland trees disappeared, riparian trees and wetland plants were sparse, and weeds and prairie taxa fluctuated from low to high values. This interval was probably the warmest, driest part of the Holocene. Zone 3 ( c. 5800 to c. 3100 BP) had a rich riparian forest, along with well-developed prairies, disturbed habitats and wetlands. This period was more moist but had intermittent droughts. Zone 4 ( c. 3100 to c. 2700 BP) has peaks in many prairie and weedy elements, whereas riparian forest elements nearly disappeared, suggesting another warm, dry interval. Zone 5 represents a return to somewhat less arid conditions and records a strong signature of introduced weeds in post-settlement time.