CAREER: Ecosystem Change in Forests and Grasslands from Decades to Millennia: A Retrospective Approach

Kansas State University, Manhattan KS

Investigators

Abstract

NATIONAL SCIENCE FOUNDATION ABSTRACT BCS - 0955225 Kendra K. McLauchlan Kansas State University The nitrogen (N) cycle is one of the planet's most critical biogeochemical cycles because N can potentially both fertilize and harm ecosystems. However, the long-term patterns of N availability in forest and grassland ecosystems are poorly understood, limiting our ability both to understand recent changes in ecosystem function and to predict future functioning. This research project will investigate changes in nutrient cycles at three sites in mid-North America in great detail during the Holocene (past 10,000 years). The research will examine contrasts in vegetation history among three sites to reconstruct past changes in N cycling and other ecosystem properties. In particular, the researchers will obtain past records that measure changes that take 10, 100, 1,000, and 10,000 years at three sites: one prairie site, one forest site, and one site that transitioned between forest and prairie during the Holocene. At each site, the researchers will measure several things (including stable N and carbon isotopes, pollen, charcoal, and selected elemental concentrations) in sediment cores taken from small lakes. Additionally, both histories in wood from living trees in the forested watersheds and a regional record of foliar chemistry from leaves preserved in herbaria near the grassland site will be obtained. The project has four main goals: 1) reconstruct the development of terrestrial N cycles over Holocene timescales at multiple sites, 2) evaluate the relative roles of vegetation, climate change, and disturbances as drivers of biogeochemical cycles on timescales from decades to millennia, 3) improve interpretations of stable N isotopes in sediment, wood, and leaf tissue on the landscape-scale, and 4) formalize a set of techniques that can be used by other researchers to determine if current human-caused changes to the global N cycle are increasing or decreasing N availability. The empirical records generated in this project will provide the first insights on Holocene N cycling as well as allow evaluation of the relative impact of human-caused N deposition on grassland and forested ecosystems in the 20th century. The research will identify ecosystem characteristics that make systems vulnerable or resistant to N pollution, particularly if the vegetation type (grassland or forest) matters. It also provides policy-relevant understanding regarding N as a potential pollutant whose deposition would be expensive to regulate. The research provides a new perspective: the retrospective approach to understanding modern global change, strengthening observational and experimental approaches. The research will provide a clear picture of the role of history in determining the effects of acute and chronic stressors on ecosystems, with important implications for N emissions. In addition to the scientific advances, the project will help train the next generation of scientists, including middle school, undergraduate, and graduate students. Finally, research results will be brought directly to the public by designing an exhibit and educational materials at the Visitors Center at Itasca State Park, Minnesota, USA.