El Niño’d: tropical field research when climate won’t sit still

Steve Roels is a PhD candidate in the Department of Integrative Biology at Michigan State University. His research asks how trophic cascades interact with tropical forest restoration. When not in Panama, he enjoys documenting biodiversity and restoring native vegetation on his own 6.2 acres of Michigan.

Tropical field biology has a lot of uncertainty built into it. The scientific community is still barely scratching the surface of tropical biodiversity and the immense complexity of biotic interactions (relationships between organisms). Biologists, myself included, often get lulled into thinking of the tropical climate as a stable abiotic backdrop that lies behind the great drama of biotic interactions. But what happens when those abiotic conditions change abruptly and dramatically?

The current El Niño event in the Pacific is now regarded by meteorologists as one of, if not the, strongest El Niño events ever recorded. The North American media understandably focuses on how El Niños affect our continent; usually wetter West Coast winters and dryer, warmer Midwest winters. What many North Americans don’t realize is that El Niño events have their most profound effects on Pacific countries in the tropics.

El Niños are one extreme of a much larger climate pattern, the Southern Oscillation. The El Niño-Southern Oscillation (ENSO) is an erratic seesaw of Pacific surface water temperatures from warm to cool (La Niña events) and back again. Temperature swings from one extreme to the other occur every few years (on average about 5) and “the switch” is often flipped very abruptly, shifting ocean currents, air pressure, and precipitation throughout the eastern Pacific. It is important to keep in mind that ENSO events are not “bad” per se, just different, and that creates biological winners and losers.

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Strong El Niño conditions in the eastern Pacific during my field season. Image from: www.ncdc.noaa.gov.

In central Panama, where I research bird communities in forest restorations, El Niño conditions generally bring warm coastal waters and drought. I say “generally” because each El Niño is like a snowflake—there are some basic patterns, but every event is unique. This El Niño is sticking to the pattern: central Panama is currently experiencing a severe drought and creating headaches for many of my colleagues at the Smithsonian Tropical Research Institute (STRI). The drought has played havoc with the frog biologists, who are waiting for mating frogs, who have, in turn, often been waiting for rain. Coral researchers are scrambling as abnormally warm waters cause coral bleaching. However, some scientists view this El Niño as an opportunity because it could be considered a proxy for future climate. The El Niño is compounding the warming effects of global climate change, putting 2015 on track to be the warmest year on record. A friend of mine who studies tree physiology and water use in forest restorations says she is getting great data. After all, a key challenge for restoration ecology is deciding what we restore to. An ecosystem that tries to match what was formerly present? Or one that will continue to thrive in an uncertain future?

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The Agua Salud restoration site. The blocks of vegetation in the landscape are different experimental tree planting treatments. Lake Gatun, part of the Panama Canal, lies in the haze on the horizon. Lake levels are anticipated to drop to record lows this dry season.

The effects of current El Niño on my own research are difficult to assess. I study trophic cascades (basically, ripples in food webs) at STRI’s Agua Salud forest restoration project, especially focusing on birds, insects, and trees. I conducted an experiment this past July-August, which is normally the heart of the wet season, but was instead a historic drought. How this drought effected tree growth, insect populations, and bird behavior—all components of my study—is hard to say. Prior research on ENSO effects on trophic relationships is limited (it’s hard to plan research around an unpredictable and irregular event!) but some long-term studies have found large ENSO effects on food webs in Panama and Chile.

When I returned to the United States after my field season and talked with my research advisor about the uncertainty the El Niño brought to my study, she said, “You’re going to hate me for saying it…” I replied, “I already know what you’re going to say.” Maybe I need to do the experiment again next year.

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