Biogeochemistry on the Range: The Established Researcher

Abstract

Photo by David Hamilton, used with permission. Anthony is much too kind. The real genesis of my interest, research, and writings about biogeochemistry began at Dartmouth College, where I rubbed shoulders with Bill Reiners and his first graduate student, Peter Vitousek. Peter and Bill's paper, “Ecosystem succession and nutrient retention—hypothesis” (1975, BioScience 25:376–381) along with Noye Johnson and his colleagues’ paper, “A working model for the variation in stream water chemistry at the Hubbard Brook Experimental Forest, New Hampshire” (1969, Water Resources Research 5:1353–1363) documented how the movement of the important nutrient elements for plants is closely controlled by biology, whereas the non-essential elements move through ecosystems, controlled by the laws of solubility and other physical processes. I have carried that observation through my subsequent work, leading to the Chihuahuan Desert in southern New Mexico. Deserts have often been overlooked by biogeochemists, as places that are too dry for much to happen that is very interesting. I differ from that opinion. In deserts, you can see the stark contrast of what is controlled by biology and what is not. In a 1990 paper, “Biological feedbacks in global desertification” (Science 247:1043–1048), my Long-Term Ecological Research (LTER) colleagues at the Jornada Experimental Range formulated the Teeter-Totter model of desertification, in which landscapes tip from grassland to shrubland when perturbed by overgrazing and other external stressors. With shrub encroachment, the model predicted that the distribution of important soil nutrients would become heterogeneous across the landscape. My 1996 paper that Anthony referred to was a test of that hypothesis: comparing the spatial variation in important soil nutrients (N and P) to non-essential elements (e.g., Na and Li) across the landscape of desert grassland and shrubland habitats. We included sites in the Mojave Desert to document the nutrient distribution in long-term shrublands and sites in the grasslands of Colorado as an example of what to expect in a long-term grassland. A few years ago, I was gratified to see research by Jobbagy and Jackson (2001, Biogeochemistry 53:51–77) showing that the differing distributions we saw across the desert landscape were paralleled by differing distributions of soil nutrients with depth in ecosystems worldwide. All these are examples of biogeochemistry—the control of the chemical conditions at the surface of the Earth, on land and at sea, by the distribution and activities of organisms. The characteristics of our planet that we consider normal would not be as they are without life on Earth. G. E. Hutchinson saw it, Alfred Redfield saw it, and Herb Bormann saw it. And, to the distress of many, these characteristics are now being upset disproportionately by a single species, Homo sapiens, whose changes to the atmosphere, climate, and biodiversity threaten the persistence of the biosphere as we have come to know it.