The 5.1 ka Aridization Event, Expansion of Piñon-Juniper Woodlands, and the Introduction of Maize (Zea mays) in the American Southwest
Brandon L. Drake, W. H. Wills, Erik B. Erhardt
The Holocene
Publication details will update here, accepted 2/13/2012
Lee Drake (UNM Anthropology) exemplifies excellence and I will make every opportunity to work with him again.
Abstract
Pollen analysis is frequently used to build climate and environmental histories. A distinct Holocene pollen series exists for Chaco Canyon, New Mexico. This study reports linear modeling and hypothesis testing of long distance dispersal pollen from radiocarbon-dated packrat middens which reveal strong relationships between piñon pine (Pinus edulis) and ponderosa pine (Pinus ponderosa). Ponderosa pollen dominates midden pollen assemblages during the early Holocene, while a rapid shift to a much higher proportion of piñon to ponderosa pine pollen between 5,440 and 5,100 BP points to an aridization episode. This shift is associated with higher δ18O values in Southwest speleothem records relative to the preceding millenium. The period of aridization is followed by a sharp increase in El Niño/Southern Oscillation events that would have caused highly variable precipitation and lasted until 4,200 BP. Bayesian changepoint analysis suggests that this aridization episode led to stable ecotonal boundaries for at least 3,000 years. The piñon/ponderosa transition may have been caused by punctuated multi-year droughts, analogous to those in the 20th century. The earliest documented instance of Zea mays cultivation on the Colorado Plateau is around ca. 4,290 BP. The introduction of this laborintensive cultigen from Mesoamerica may have been facilitated by changes in the regional ecosystems, specifically by an increase in piñon trees, that promoted increasing human territoriality. Linear modeling and hypothesis testing can complement traditional palynological techniques by adding greater resolution in vegetation patterning to climate/environmental histories.
Research, stable isotopes, Statistics
We got one! Research Allocation Committee (RAC) Grants are for supporting new research or creative works. The RAC is particularly supportive of projects that may lead to outside funding and/or larger related projects.
PIs: Erik Erhardt and David Hanson
Title: “Frequentist (bootstrap) and Bayesian modeling of (photo)respiration in plants”
Amount: $3982.63, RAC 12-04
Use: To hire statistics graduate student, Mohammad Hattab, to implement and develop modeling that I did last summer in Switzerland.
Purpose:
We are requesting $3982.63 to develop statistical models to estimate (photo)respiration in plants, accounting for sources of uncertainty and prior information. Because current models provide estimates without meaningful assessments of uncertainty, our model will have broad application in understanding photosynthetic pathways and carbon usage in plants, clarifying the precision of our knowledge, conditional on what is already believed. This modeling is an important step towards developing more comprehensive models of photosynthetic parameters. Support from the Resource Allocation Committee will allow us to: (1) develop frequentist (bootstrap) and Bayesian models to analyze existing experimental data, providing inferences on the set of parameters related in the model; (2) design experiments and acquire additional data to distinguish and estimate respiration and photorespiration under a set of scientifically relevant conditions; (3) conduct validations using pre-existing data and estimates; (4) publish our model with results; and (5) develop grant proposals to apply this model more broadly.
Research, stable isotopes, Statistics
Last year David Hanson and I began collaboration continuing his study in leaf respiration. I wrote a custom R package to process data from his tunable diode laser (TDL) and Licor devices to understand how carbon is taken up and respired by leaves. This summer a poster presenting some of what we’ve been learning was presented by graduate student, Dianne Pater, who has been designing and running experiments.
DT Pater, EB Erhardt, and DT Hanson. Isotopic signature of photorespiration. In Joint Annual Meetings of the American Society of Plant Biologists and the Canadian Society of Plant Physiologists, Montreal, CA, August 2010.
Research, stable isotopes
In a previous post I discussed this paper and how fun it was to write with Laurel. Here I’m happy to report it’s available electronically (SpringerLink, pdf) and soon in paper.
Laurel K. Goode, Erik B. Erhardt, Louis S. Santiago, Michael F. Allen. Carbon stable isotopic composition of soluble sugars in Tillandsia epiphytes varies in response to shifts in habitat. Oecologia (2010) 163:583–590.
DOI 10.1007/s00442-010-1577-5
Received: 11 March 2009 / Accepted: 25 January 2010 / Published online: 13 February 2010
Research, stable isotopes, Statistics
A few important areas of focus, reflecting what I’m doing and where I’m going. Read more…
MIND, Research, stable isotopes, Statistics
Laurel Goode, Erik Erhardt, Louis Santiago, and Michael Allen.
δ13C of soluble sugars in Tillandsia epiphytes vary in response to shifts in habitat.
Oecologia, Physiological ecology section, 2010.
I met Laurel at SIRFER 2008 where we enjoyed a wide range of stable isotope lectures and lab experience. She first used my software, SISUS, to estimate the proportion of C3 vs CAM photosynthesis of epiphytes. Our work and friendship led to the collaboration where we thought about and developed a model for the environmental factors affecting the phothsynthetic pathways of the species studied. Read more…
stable isotopes, Statistics
Christopher P. Bickford, Nate G. Mcdowell, Erik Barry Erhardt, Heath H. Powers, David T. Hanson. (2009)
“High frequency field measurements of diurnal carbon isotope discrimination and internal conductance in a semi-arid species, Juniperus monosperma“.
Plant, Cell & Environment, In print (1/28/09). Read more…
stable isotopes