In 1989, David Tilman asked: what is the typical time scale of ecological studies? He found that 86% of experimental studies lasted 3 or fewer field seasons. Observational studies faired only slightly better: "Most of the studies greater than 10 years and all of the studies greater than 50 years were based on chronosquences and paleoecological reconstructions and not on direct observation." Why was Tilman concerned? Because ecological systems are complex, and the immediate response to a manipulation may only represent transient dynamics not the steady-state response of the system.
Twenty years later, the need for long-term experimental manipulations is, in our opinion, even greater. Ecosystems are complex. They are comprised of species with divergent body sizes, generation times, and abilities to evolve in response to changed conditions. The abiotic environment (for example: temperature, humidity, etc) can change from hour-to-hour, season-to-season, year-to-year, or exhibit decadal or longer cycles. This complexity creates a variety of ecological dynamics on short-, medium-, long-, and even geologic time scales. While long-term studies have become more common, it undoubtedly true that most studies greater than 50 years are still not the result of direct observation. This means we continue to have little or no idea what the long-term responses of ecosystems may be to perturbations.
Studies like the Portal Project are critical to our understanding of how seemingly simple manipulations can result in complex and unexpected long-term dynamics. For 30 years we have been monitoring a 20 ha piece of the Chihuahuan Desert and observing its continually surprising response to the removal of dominant species. Please explore our website to learn more about this important study, what we've been doing, what we've learned, and what we're doing right now.