New study looks at how coastal ecosystems respond to hurricanes

Saint Paul, Minn. – When confronted by a storm, is it better to be resistant like an oak or resilient like a willow? That’s the long-standing question an international research team that included Macalester professor Christine Sierra O’Connell examines in a new study of the ecological impacts of hurricanes.

The team’s findings, reported in the March 2 issue of Science Advances, could help guide decision makers as they plan for climate change and aim to protect a coastal population threatened by tropical storms that are growing more intense and tracking farther north. The results also provide a framework for addressing other kinds of disturbances, such as nutrient pollution or wildfires, that affect more landlocked areas like the Upper Midwest. 

Dr. O’Connell is an assistant professor of environmental studies and was one of 23 scientists from 11 states, Puerto Rico and Taiwan who contributed to the study.

What are the paper’s most significant findings?

The big picture of this study is that a group of researchers asked the question: When a tropical cyclone, a.k.a. a hurricane, hits an ecosystem, how does that ecosystem respond? One of the core underlying questions is, as an ecosystem, how likely are you to show some sort of tradeoff between being resilient to a storm and being resistant? If an ecosystem is resistant to a storm, it might not suffer as much initial intense disturbance or damage. If it’s resilient, it might be more impacted at the outset, but it might bounce back more quickly. And in fact, the study’s biggest result is that it found a consistent pattern of trade-offs across ecosystems, in which ecosystems either tended to be more resilient to these tropical cyclones or resistant to them.

How does this study alter what was previously known about the impact hurricanes have on ecosystems?

The amount of data used in this study is extremely rich and robust, and the findings are very consistent across ecosystem type, storm intensity and ecosystem variables. The study includes over 4,000 different time series that were observed by scientists and ecologists after 26 different storms between 1985 and 2018. This is 40 years of data looking at variables as disparate as soil carbon changes and tree mortality to how animals and plants were responding to these storms. So these overall findings – that there is this tradeoff between resistance and resilience after a big hurricane – was robust across many different storms, where on the globe they occured, and what kind of ecological data was being analyzed. And that’s just really exciting and cool. Whenever you can take all different types of data, combine them to compare apples and oranges, and then find something that’s true across all of it? That makes us feel really confident and excited about the results. 

What was your role in the study?

My research looks at climate-driven disturbances and how they’re altering tropical rainforests. My role in the study was to contribute some of the data that I collected after Hurricanes Irma and Maria hit the island of Puerto Rico. One of the field sites where I work is called the Luquillo Long-Term Ecological Research program which is located on the eastern side of the island. In the immediate wake of Hurricanes Irma and Maria, we were able to track a number of soil variables over time for about a year and a half. We were specifically interested in how soil carbon would be impacted by these hurricane disturbances, as well as the soil’s moisture and temperature and whether nutrients became more or less available in the wake of a hurricane. 

What’s the big picture takeaway for you?

A really big picture takeaway is that we know humans are altering disturbance regimes and ecosystems all over the globe. And by disturbance regimes, I just mean how frequently there’s a disturbance such as a hurricane, flood, drought, or pollution that disrupts the ecology of a system. What does that disturbance do to the amount of carbon that’s stored in that ecosystem? For instance, do more frequent or more severe hurricanes lead to an ecosystem holding less carbon overall? And if an ecosystem is holding less carbon, that carbon is almost certainly in the atmosphere and potentially warming the planet even faster. So there are these ideas that climatic change can lead to ecosystem feedbacks and then further accelerate climatic change. There are a lot of unknowns in that dynamic that we’re very interested in trying to figure out.

Another really interesting area of inquiry to pursue is to look at how you actually put this new knowledge into action. What does this mean for conservation managers who might need to make decisions about how to restore plant communities or how to protect bird species, for example? 

This study focuses on disturbances caused by tropical cyclones. How can the findings be applied to help us better understand and address other kinds of disturbances, such as wildfire and nutrient pollution, that are more likely to occur in more landlocked ecosystems like Minnesota’s?

I think one of the most exciting things about this study is that because it’s so robust across types of ecological responses and types of ecosystems and parts of the world, it also makes us think that we might have tapped into a more universal rule about how ecosystems might respond to disturbances. Are they more likely to be resilient or resistant? There’s no indication that this kind of response tradeoff applies only to hurricanes. So you might also imagine that this tradeoff between resistance and resilience could play out in ecosystems experiencing fire disturbance, for instance, or nutrient pollution disturbance like we see a lot here in the Upper Midwest.  Humans are changing patterns of disturbance across ecosystems broadly, so it’s crucial that we explore what the consequences of those changes might be.