MY RESEARCH

My Google Scholar

I have over a decade of experience in research ecology working in ecosystems as diverse as post-eruption volcanoes, pacific islands and the Great Plains, and I have studied topics as varied as plant-herbivore interactions, climate change, succession, exotic species invasion and plant maternal effects. Among all of this, my most substantial independent research experience is an investigation into how drought timing affects ecosystems. I investigated this question in both the tallgrass prairie and the sagebrush steppe. 

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My inquiry into how drought timing affects ecosystems began with my Master’s work at Colorado State University. For my Master’s thesis I devised a project investigating the response to drought timing in the tallgrass prairie by imposing a 30% reduction in growing season precipitation at three different time points throughout the growing season. I monitored ecosystem response by measuring both above and belowground primary productivity as well as soil moisture and nutrient exchange. I also estimated response to drought while it was actually occurring by measuring change in light penetration through the grass canopy because plants grow less and wilt under drought conditions. 

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I found that based on light penetration, aboveground growth was reduced in all seasons of drought. However, end of season aboveground primary productivity indicated that only the middle and late droughts mattered in terms of forage production. Additionally, the reduction in growth in the middle drought was not as large as the reduction in canopy seen during the drought. This indicates that the tallgrass prairie ecosystem has substantial ability to recover from drought within the growing season. The tallgrass prairie can recover functionality from an early and to some extent mid- season drought, but not a late drought. It looked like similar trends might be occurring belowground, but variation in the belowground biomass data was high enough that those trends weren’t statistically significant.

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The sagebrush steppe is a very different ecosystem than the tallgrass prairie, the former being a cool season grass and shrubland that receives most of its precipitation overwinter and precipitation patterns are highly variable from year to year. The tallgrass prairie, on the other hand, is primarily a C4 photosynthesis system with a bimodal precipitation pattern with large amounts of rainfall in both the winter and summer months. Precipitation is still variable from year to year, but not nearly so much as in the sagebrush system. When I began working in the sagebrush steppe with the Agricultural Research Service I was interested in how this ecosystem might respond differently to changes in drought timing as compared to the tallgrass ecosystem. I suspected that the sagebrush ecosystem would be most sensitive to a mid-season drought because there would be lots of soil moisture remaining in the early season from winter snows, making a true drought difficult to impose even when precipitation was removed. And I suspected a late season drought would have a lesser effect because of the dominance of C3 species which tend to grow early in the season so that most growth would be completed even before normal rains had stopped. 

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To find out if my assumptions were correct ,I installed an improved version of my project from my Master’s thesis in the sagebrush steppe. It had a higher sample size and more extensive sensor network than my original study so that I would be able to better detect patterns of change. I also measured a number of additional factors insights from my first study indicated would be beneficial. The most important of these was monitoring within-drought growth both above and belowground directly. In my previous study I had only been able to estimate this with light penetration data for above ground growth, and had no metric to measure what was happening below ground at all during the drought. I also monitored reproductive effort of key species and checked for actual water stress in plants by measuring water potential during droughts, and I collected data the year after the drought to determine how drought timing may influence legacy effects.

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While not all of the data has yet been analyzed I can tell you that the early, mid and late droughts all reduced the amount of soil moisture available in plots. Water stress was evident in key species during drought, particularly those species that grow earlier in the growing season: Alyssum desertorum, an early season annual forb, and Poa secunda, an early season perennial grass. Other species only experienced drought stress during the middle drought -- Achnatherum thurberianum, a later season perennial grass that stays green throughout the growing season, and some did not experience drought at all -- sagebrush, a deep root perennial shrub did not experience water stress regardless of when the drought occurred, presumably because it’s roots allowed it access to the water table and deep soil moisture. 

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Root growth data also indicated that the middle drought period was the most important in terms of ecological response. Roots produced in the drought plots were only half that of the control plots during the middle drought. This reduction seems to have been principally in roots in the upper 10 cm of soil. However, the sagebrush steppe ecosystem appears to be remarkably resilient. By the end of season all drought plots and controls had similar amounts of root growth at all soil depths indicating that those plots that had seen severe reduction in root growth in the middle of the growing season had been able to fully recover. As I have not yet finished processing the samples, I don’t know if the same trends were evident above ground, however, I do know that very small reductions in seed production were found in all species measured under drought conditions. However, the timing of drought did not influence this reduction. 

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This series of projects was led entirely by me as the primary investigator. I did the background research to design both drought timing experiments. I installed the projects and conducted the field work along with seasonal assistants I hired. I’ve conducted the data analysis and interpretations and used my findings to assemble presentations for professional societies and publications. 

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However, studying drought timing is not my only work dealing with the effects of  drought on ecosystems. I am also part of the Extreme Drought in the Grasslands Experiment out in the Great Plains and am partnering with several scientists in Eastern Oregon to set up a DroughtNet site as part of that large experimental network. I am considered an upcoming specialist on the effects of drought in dryland systems.