A pair of rainout shelters deployed in the field.
Resilience. What is it?
In psychological terms, it is the ability of an individual to recover from a shock. This can be quantified by answering a few questions: how big was the shock? How long did it take to recover? To what state has the patient recovered to? Are they more or less the same person as before?
In ecological terms, the definition becomes more uncertain. Some have attempted to characterize it in the same way as in psychology, with recovery time to some 'pre-disturbance' state. But what on Earth is a 'pre-disturbance' state? How does one quantify the change? Why assume that there is a stable equilibrium around which a system ought to exist?
Carpenter and his co-authors (2001) give a compelling alternative to the psychological definition of resilience when they state that in ecology, we must measure the resilience of what, to what. This is the key to developing a measurable metric of resilience in an ecological system. Resilience is characterized in these systems by a domain of attraction which an ecosystem tends to fall into, with certain defining traits that can be monitored and measured.
This is where my study comes into play. Over the past few days, I have been busily constructing sixteen 2.4mx2.4m shelters designed to passively intercepts about 80% of incoming moisture, simulating a long-term disturbance (drought) that is a constant concern in prairie systems, a concern that is becoming more prevalent as climate change alters rainfall patterns and makes summer droughts ever more common and intense.
Above is one of my pairs of shelters, deployed in a plot planted in 2010 with only Big Bluestem grass (but which has since grown in with several other species, including dandelions, goldenrod, and lambs quarters, among other native and introduced species). The plots are about 3/4-acre each, four planted with Big Bluestem, four with a high-diversity grass and forb mixture. To these rainout treatments I will add other disturbances related to human-induced landscape change, including smooth Brome invasions, nitrogen deposition, and biomass cutting (to simulate haying). These prairie plots represent well-maintained, well-established restorations, and their responses should be indicative of the ability of different levels of diversity to withstand the shocks of multiple disturbances.
Does greater diversity confer greater resilience? How would we measure this if it does? What parameters are important for describing ecosystem resilience? Again, it is the resilience of something to something else that we must focus on. I've described the to what. But what factors are important in maintaining an ecosystem's identity? What factors do I expect to change?
My personal interest lies in nutrient cycling, in the ability of a community to mediate flows of nutrients and energy through its component parts, and how this ability is related to overall ecosystem health. To that end, I hope to quantify the soil moisture, plant water use, and nitrogen mineralization and carbon:nitrogen ratios within plant tissues. On a broader scale, I am interested in changes in community composition, reproductive potential, and how long my plants last through a growing season when faced with multiple interacting stressors (as even exceptional nutrient cycling is only useful for a system so long as the plants are alive).
In the end, I hope to quantify a suite of parameters that will enable researchers to make better predictions about the fate of their restorations and prairie remnants under various pressures, and to be able to say something about the nature of resilience in a large-scale restoration (most have been done only in very small greenhouse experiments).
So far, I have these shelters. It's just the first step, but it's a giant one for me. Viewing these roofs from the road as I drove away yesterday after building them, I was filled with anticipation. I have tangible proof, now, that this is going to happen. I am going to experiment with these plots, gather data, gain insights. Even if nothing else in this entire study works out, I will have spent my time well, exploring these plots and learning about the ways they live and die. And I will have the knowledge that people care about these systems, enough to pay a poor graduate student like myself to go out and wreak havoc on these poor plant communities just to see how they respond.
It's going to be a lot of work. And a lot of fun.