My research concerns the impacts of human activity and Quaternary climate change on vegetation and landscapes of tropical Latin America, the Caribbean, and the southeastern U.S.  With collaborators and students from the University of Tennessee, other U.S. universities, and foreign universities and research centers, I have examined environmental changes that have occurred over time scales ranging from less than ten years to over 10,000 years.  Much of my work focuses on climate and landscape change over longer time scales, as reconstructed from analyses of pollen grains, charcoal fragments, diatoms, stable isotopes, and other proxy indicators in ancient lake and swamp sediments.  I have worked extensively in Costa Rica, where my students and collaborators and I have assembled datasets on prehistoric agriculture and fire and climate history in lowland rain forests, dry forests, and savannas, and on climate and fire history in montane oak forests and the shrub-dominated páramos that occur above the upper forest limit.  To provide a basis for the interpretation of pollen and diatom assemblages, we have studied modern lakes and their sediments at sites throughout the country.  I am also involved in several projects on environmental history in the Caribbean and tropical Atlantic region, in the Andean highlands of Ecuador, and in the Amazon lowlands of Ecuador, Peru, and Bolivia.  At some of these sites we are investigating tree-ring evidence of environmental history along with evidence from sediment and soils.  I am also very interested in fire ecology, and have carried out research on the impact of recent fires on highland páramo vegetation in Costa Rica and on shrublands and pine forests in the mountains of the Dominican Republic. 

 

With Dr. Ken Orvis of the Department of Geography, I co-direct a suite of laboratories in the Science and Engineering Research Facility that together make up the Laboratory of Paleoenvironmental Research.  These include facilities for the study of ancient soils and sediments (and the plant and other fossils they contain) as recorders of past environmental conditions including past climate, vegetation, fire, and human history; of modern soils and sediments and their environmental relationships; and of modern and historic landscapes and climate.  The analysis and modeling of contemporary patterns and processes are of interest in their own right, and are also fundamental to our ability to understand evidence of past conditions preserved in soils and sediments and to apply this knowledge to questions of future global change.  The Laboratory of Paleoenvironmental Research originally included a small tree-ring lab, which was subsequently spun off and developed by Dr. Henri Grissino-Mayer into the Laboratory of Tree-Ring Science (of which Grissino-Mayer is Director and Dr. Orvis and I are Associate Directors).  The Laboratory of Paleoenvironmental Research collaborates with the Laboratory of Tree-Ring Science, with Dr. Claudia Mora’s Stable Isotope Lab, with other labs at UTK through the Global Environmental Change Research Group, and with laboratories at other universities and research centers. 

Click here for a list of Professor Horn's recent publications