Iowa's natural features have always been characterized by changes of the types depicted in this newsletter's lead article. One of CGRER's missions is to track the direction and rate of that change, and to determine how normal change might be mutating into something abnormal and threatening to the Earth's life support systems. In order to gauge "normal change," we need a standard of comparison; that standard is the past. Herein lies the significance of the research of several CGRER members at the University of Iowa, all of whom are attempting to outline past climates, landscapes, and ecosystems as accurately and specifically as possible. Dick Baker, working often with other CGRER members, has spent his career investigating the ancient communities and climates of Iowa and the Midwest. By identifying tiny fossil pollen grains and seeds, Dick has traced the ebb and flow of plant communities as the climate has changed: lush boreal forests of spruce, larch, and pine which thrived here 30,000 years ago, giving way as the climate cooled to scraggly spruce stands, and finally to genuine arctic tundra during the maximum extension of the most recent glaciers 18,000 years before the present. Tundra animals and plants then crept northward as the glaciers melted and climate warmed, and eventually the true tallgrass prairie developed, starting 9,000 years ago in western Iowa. These prairies and their associated savannas, woodlands, and wetlands survived to greet the settlers in the 1800s. Through this research, we now know that arctic tundra was once securely established in Iowa, nearly 300 miles (or 500 km) farther south than anyone had previously thought. These researchers also determined that the prairie's establishment was accompanied by large and complex local variations.For example, during western Iowa's hottest, driest period, about 6,000 years ago, northeastern Iowa and surrounding lands in Wisconsin and minnesota were covered with lush forests of maple, basswood, and similar moisture requiring species.
Before Dick began his work, little was known specifically about Iowa's ancient ecosystems. In other regions, such information was gleaned from the corings of sediments in bogs and lakes, but Iowa had few suitable coring sites. Baker's research has been based on new research techniques - the analysis of plant remains in samples dug from saturated streambanks, for example - and these have allowed an entirely new understanding of our land's past.
These new techniques have provided several independent confirmations of the dating of past events. Botanist Diana Horton has demonstrated that changes among vascular plants are mirrored perfectly by changes in mosses - those mosses typical of deciduous forests disappearing, for example, exactly when Baker dated the forest giving way to prairie. The research of geologists Luis Gonzalez and Mark Reagan has provided equally strong verification of changes in the climatic regime. Gonzalez and Regan, who examine and date the minuscule annual bands of stalagmites from caves and test them to determine concentrations of various isotopes, can use their data to establish very accurately the mean annual temperature of the specific region where the cave is located, its rainfall, biomass turnover rates, and even changes in vegetation above the cave. Their tests also confirm Baker's dates with startling accuracy.
Art Bettis adds another facet to the Baker team's research. Bettis examines the study sites to outline facets of alluvial stratigraphy and soil formation of past years. He gains information on the shape and formation of stream meander belts, downcutting patterns, and controlling features of stream behavior. In addition to identifying physical parameters of the Baker team's sample sites, Bettis's research is helping to determine how to control modern-day problems such as excessive river sediment loads.
In independent studies, geologist Holmes Semken has been working on the paleoecology of fossil mammals recovered from deposits that are younger than 40,000 years. He has documented that species now separated into distinct biomes, e.g. boreal forest and southern deciduous forest, coexisted in the same geographic area during the Ice Ages. However additional research, which involves correspondence analysis of the animals of post-glacial archaeological and paleontological sites, demonstrated that the method (the screen size) used to recover the fossil fauna accounted for most of the variation among sites and has led to erroneous paleoecological interpretations.
The Baker team has also examined the most recent changes in Iowa's ecosystems, those associated with EuroAmerican settlement and the establishment of intensive agriculture during the past 150 years. They have documented the inadvertent results of this transformation: massive erosion of uplands causing deposition of 1 to 2 meters of sediment across a creek floodplain; the rapid turnover of the land to fewer and more aggressive plant species; the decimation of insect fauna; degradation of stream quality.
In related research, Horton has been surveying Iowa sites for surviving remnants of now-endangered plants. Another CGRER member and botanist, Steve Hendrix, focuses on Iowa's prairies, the once-dominant native ecosystem. Through several ongoing studies, he is assessing the multiple effects of the settlement-induced habitat fragmentation (the cutting of once-extensive ecosystems into tiny surviving pieces) on the ability of prairie plants to grow and reproduce successfully, and to form new, viable populations on restoration sites.
CGRER members also have been looking into the Midwest's more distant past. Gonzalez, who now applies his stalagmite analysis to events in the last 10,000 years, believes that his techniques could trace events up to 350,000 years ago. Art Bettis, a geologist with the Iowa Geological Survey Bureau, is attempting to reconstruct the mid-continent's vegetation, climate, and soil formation during the last interglacial period, from 80,000 to 120,000 years ago, when higher temperatures and atmospheric CO2 concentrations resembled what we might be facing in our own future.
Greg Ludvigson, also a geologist with the Iowa Geological Survey Bureau, is thinking about the even-more-distant past: the mid-Cretaceous, about 100 million years ago. During this "Age of Dinosaurs," the Earth as a whole was much warmer than now - it was a "greenhouse world" perhaps uncomfortably similar to the Earth that global warming might eventually create. By using fossil pollen and spores to develop a time sequence through that period and through investigations of stable isotope paleohydrology, Ludvigson and colleagues are reconstructing the environments of those times, in particular their hydrologic conditions and climatic regimes.
These CGRER members who study Iowa's near and distant past are contributing the baseline against which we will measure future global change projections. These types of reconstructions are crucial for testing and calibrating computer models that predict the consequences of global warming. Reconstructions should help us place current environmental changes in perspective - to discriminate between what changes are natural and normal, and which ones are aggravated by human-induced perturbations of the environment. Such reconstructions also provide a real-life idea of how living systems might respond to various global change scenarios. By studying how climate, landscape, and life interacted in the past, we can better understand how vegetation may change in relation to future global warming, how future climate change will affect landscape development, and other such links that will determine the parameters of future life on Earth.