Ephemeral Wetlands and Climate Change: Implications for Frogs and Toads

Eastern narrow-mouthed toad eggs float on the surface of shallow waters. All amphibians require water – whether a pond, puddle, or temporary wetland – for breeding. Photo by Fredlyfish4, courtesy of Wikimedia Commons.
Eastern narrow-mouthed toad eggs float on the surface of shallow waters. All amphibians require water – whether a pond, puddle, or temporary wetland – for breeding. Photo by Fredlyfish4, courtesy of Wikimedia Commons.

Many frog and toad species live on land as adults, but their lives always begin in water. Depending on the species, dozens or hundreds of eggs, bound together into a gelatinous glob or string, are laid in a pond, puddle, or marsh. When frogs and toads spawn in waters inhabited by fish, many of the eggs and tadpoles are eaten. “Many species of frogs and toads are more successful breeding in ephemeral, or temporary wetlands that are not inhabited by fish,” says U.S. Forest Service scientist Katie Greenberg. “Ephemeral wetlands can produce thousands of juvenile frogs and toads each year.”

The very existence of ephemeral wetlands is affected by rain, making them sensitive to altered weather patterns caused by climate change. Although ephemeral wetlands usually dry out sometime during the year, drought causes them to dry up much sooner. Without water, amphibian eggs – as well as tadpoles that have not developed lungs yet – die.

Greenberg, a research ecologist at the Forest Service Southern Research Station (SRS) Upland Hardwood Ecology and Management unit, is lead author of a new study that evaluates how climate change could affect ephemeral wetlands and amphibian species that depend on them. The study was recently published in the journal Wetlands.

For 17 years, Greenberg and her colleagues measured precipitation, air temperature, and water depth in 8 small ephemeral wetlands in the Ocala National Forest, Florida. All 8 wetlands were sinkholes, and the amount of water in them depended on groundwater rather than streams.

Greenberg and her colleagues used the data to develop a model for predicting seasonal levels of water in the wetlands, and then used the model to forecast future wetland conditions and how they might be affected by climate change. They then used the model to forecast weekly water depth in the wetlands for the years 2012 – 2060. “In our models, temperature was not a significant factor in predicting how long a wetland would stay flooded,” says Greenberg. “The most important factors were precipitation and water depth from the week before.”

“We used one of many available climate projections to show how our wetland hydrology model can be used to test alternative climate change scenarios,” says Greenberg. “We do not suggest that this or any other scenario in particular will actually occur, but wanted to illustrate how our model can be used as a planning tool, to explore how these kinds of wetlands could be affected by climate change.” Under the scenario the scientists selected, the model indicated that in the future, ephemeral wetlands in the study area could be shallower and dry out sooner in the season. If scientists had selected a different scenario the results would have been different.

Greenberg and her colleagues examined the breeding requirements for five frog and toad species, such as the duration and timing of water in ponds, and found that the potential changes would likely benefit one of the species, but that the other four species would not be able to successfully breed during most years, because ponds would dry too quickly for the tadpoles to develop into young frogs. If this climate scenario played out, wetland conditions in the study area could cause populations of some species to decline or become locally extinct.

Predicting how climate change will affect small areas is difficult, but the uncertainties show the importance of conserving multiple wetlands. Ephemeral wetlands can vary significantly. Some may be dry when others are wet, and some have deeper water that lasts longer than others. The variation between ephemeral wetlands means that climate change will affect them – and the species which depend upon them – in different ways. “Conserving multiple wetlands will maximize the habitat available to frogs and toads,” says Greenberg. “This model will be useful to land managers and planners who want to explore potential changes in ephemeral, groundwater-driven sinkhole wetlands and how those changes could affect amphibian populations.”

Read the full text of the article.  

For more information, email Katie Greenberg at kgreenberg@fs.fed.us.

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