Masters Theses

Date of Award

8-1994

Degree Type

Thesis

Degree Name

Master of Science

Major

Geography

Major Professor

Sally P. Horn

Committee Members

Paul Delcourt, Carol Harden, Lydia Pulsipher

Abstract

Issues of where, when, how, and to what extent preColumbian humans affected the natural landscapes of Central America have been debated for years. While many studies have been conducted in Guatemala and other areas of Olmec, Aztec, and Mayan influence,little attention has been paid to peripheral areas. It has been suggested that indigenous populations were small in countries such as Costa Rica, Nicaragua, and northern Panama(Origgi 1981), but little is known about how these sparse populations affected their environment. As part of a broader study aimed at exploring prehistoric human-environment relationships throughout the Central Atlantic watershed of Costa Rica, several lake sediment and soil cores were obtained from two lowland tropical lakes -- LagunaBonilla and Laguna Bonillita. The lakes are located in a region of Costa Rica that has been used for millennia as a trade route by both northern and southern cultures. Many Archaeological sites are located within the region and much work has been carried out to establish archaeological sequences for the area. While the archaeology of the area is fairly well established, very little is known about prehistoric vegetation patterns, disturbance factors, and human-induced environmental change.

This thesis provides some of the first direct evidence of preColumbian human impacts on vegetation in the tropical wet lowland rainforests of Costa Rica. Paleoecological Profiles constructed from the analysis of pollen grains, charcoal fragments, and sediment characteristics provide a continuous record of human occupation in the two lake basins since pre Columbian times. The paleoecological sequence of Laguna Bonillita firmly establishes human settlement within the lake basin before 2560 yr B.P. But problems with the presence of old carbon within the lake system at Laguna Bonilla has made the radiocarbon dating of these sediments difficult. Zea is the only food crop that was identified in the pollen assemblages in the lake sediments, and the relatively high abundance(up to 5 percent of total pollen) of this heavy pollen type indicates that the crop was being grown on or near the lake margin. The lake sediment analyses document wide scale forest disturbance in the basins during the past several thousand years. Macroscopic charcoal present in soil cores from the Laguna Bonillita basin record fire as an important disturbance factor in the late Holocene.

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