All along the coast, species have adapted to the periodic pummeling of hurricanes. Bull sharks sense a pressure shift and evacuate the estuaries. Coastal pines slow their growth. Feebler species may get gutted but are quick to bounce back.
These adaptations boil down to resistance and resilience, both key survival strategies in the field of disturbance ecology. They’re also central to land management conversations, where some say they’re overused to the point of jargon.
“What I was seeing in the literature and in management circles was that resistance and resilience are kind of catchwords,” said Christopher Patrick, an assistant professor at the Virginia Institute of Marine Science. The words are often mentioned together, suggesting that increasing one benefits the other. And what land manager wouldn’t want to boost both?
But a recent publication in Science Advances determined that nature can’t have it both ways. Regardless of location, latitude, climate, or conditions, there’s always a trade-off between resistance and resilience when it comes to hurricanes.
Tempests Trigger Trade-offs from Texas to Taiwan
The research leading to this study started in 2017, thanks to Hurricane Harvey.
“I wasn’t a disturbance ecologist before Hurricane Harvey, but I kind of had to become one,” said Patrick. He was researching coastal rivers and lagoons in Texas when the hurricane hit, and he received funding from the National Science Foundation under its Rapid Response Research (RAPID) initiative, which capitalizes on fleeting research opportunities. He wasn’t the only one. The 2017 Atlantic hurricane season was the costliest in history, and dozens of researchers received funding to study their own corner of ecology, from coral reefs to seagrass meadows.
Patrick, though, wanted to understand coastal responses on a broader scale. He connected with colleagues in 11 states, Puerto Rico, and Taiwan to create a research network and start building conceptual models from their morass of data.
The authors first defined the two terms, with resistance being “the degree to which an ecosystem can remain unchanged” and resilience being an ecosystem’s ability to return to a reference state. They organized time series into four ecosystems (freshwater, saltwater, wetland, and terrestrial) and five categories: mobile animals, sedentary animals, vascular plants, biogeochemistry (including plankton and microbes), and hydrography (water conditions like salinity and turbidity).
Across 4,138 time series from 26 tropical storms, the authors found a clear trade-off between resistance and resilience. No time series was successfully both resistant and resilient nor especially bad at both either. Every species and response variable was optimized. The pattern is rare in the literature, said Patrick, let alone with such a massive data set.
“It makes sense that organisms wouldn’t be great at both resistance and resilience, considering the different life history strategies of organisms,” said Giovanna McClenachan, director of the Coastal Disturbance Ecology Lab at Nicholls State University in Louisiana. “What was really cool to me was actually seeing real-world examples that back up the theory,” she said. “I think it’s unusual to find it line up so well.”
Principles of Management
Transitioning from theory to evidence was part one. The next step is application.
Land managers have their own set of trade-offs to consider. A picnic ground, a cultural site, and a wilderness area all have different factors affecting management. “The decisions we made [after Hurricane Sandy] varied depending on those trade-offs,” said Amanda Babson, a coastal landscape adaptation coordinator for the National Park Service based in Rhode Island.
In recent years, federal land management agencies have started using the Resist-Accept-Direct framework for decisionmaking. The guidance presents resilience as a category of resistance, but this new study indicates resilience would be better placed under the accept category. “It’s fascinating that you can’t manage for both,” Babson noted.
Although the study has clear value for land managers, both Babson and McClenachan voiced concern over the historical time frame. “Unfortunately, I don’t know how much we can use the past any longer to predict the future,” said McClenachan.
She also questioned the duality of resistance versus resilience. “My biggest takeaway is you’re going to have variables and factors that are both resistant and resilient,” she said. The goal should be to manage multiple factors for the overall health of the ecosystem. “Your best bet moving forward is having more redundancy in the system.”
That depends on context, Patrick said. Smaller systems have fewer factors. As managers home in on individual marshes or mangrove forests, the results show they’ll benefit from choosing resistance or resilience.
An Impossible Task
The recently published study is admittedly a first step. “We have a laundry list of hypotheses and questions,” Patrick said. Do different populations adapt on the basis of their frequency of experiencing hurricane hits? Do droughts and floods change anything? And how does all this affect human populations?
That last question is especially appealing to Babson. Land managers often have to decide between, for example, replacing a road or letting a sand dune migrate instead. “Having a way to couple the human and natural systems together would be really great,” she said.
For now, the study elevates resistance and resilience beyond the realm of jargon and leaves land managers with a clear-cut message. According to the authors, the results imply that “managers seeking to simultaneously enhance both resistance and resilience in coastal ecosystems face an impossible task.”
—J. Besl (@J_Besl), Science Writer