Skunk Cabbage in vernal pool. Crosswicks Audubon Wildlife Sanctuary. Photo by Donna L. Long.

Vernal Pools

Skunk Cabbage in vernal pool. Crosswicks Audubon Wildlife Sanctuary. Photo by Donna L. Long.
Skunk Cabbage in a vernal pool. Crosswicks Audubon Wildlife Sanctuary. Photo by Donna L. Long.

It is spring and time to head out to some of my favorite vernal pools. Vernal pools are small pools of water that appear and dry up as the seasons change. Vernal pools are isolated wetlands because they are not permanently connected to other bodies of water. They are fascinating but rare ecosystems.

Vernal pools happen all over the globe. The temporary pools are called by different terms depending on the local language and history. In the western part of the United States, temporary pools are called prairie potholes or in grasslands, playas.

A staggering percentage of vernal pools across North America have been destroyed. In California, 90% have been destroyed. The pools were paved, built on or drained to be replaced with human-built structures. Some vernal pools were deepened and used to water cattle.

Creating new vernal pools is difficult as humans often can’t get the slopes right or the edges the right width.

 

A vernal pool in Santa Rosa Plateau, California. Geographer at English Wikipedia
A vernal pool in Santa Rosa Plateau, California. Geographer at English Wikipedia

Vernal pools appear in swallow depressions:

  • in clayey mineral soils
  • in an upland (higher elevation) area
  • in a wetland area in a low lying area
  • in the floodplain of a stream or river
  • in a forested landscape or historically forested area in northeastern North America
  • in an agricultural field or residential area

Vernal pools fill with winter rains and snow melt. As the weather warms, the water in vernal pools evaporate.  The temporary pools disappear and may return with the next winter’s snow and rain. Some vernal pools dry out every year, other every few years. But the drying out period is key to having the ecosystem of a temporary or vernal pond. If a temporary pond is filled with water in the autumn, it is often called an autumnal pond.

These toad tadpoles are probably Bufo americanus (American Toad). Photo by Donna L. Long.

Animals which breed and spend part of their life cycle in vernal pools thrive without a top predator such as fish. These temporary wetlands are a safer breeding ground for frogs, toads, and salamanders than wetlands where fish live. Fish would eat the eggs, larva, and juveniles of these animals if they were present. This dry cycle prevents almost all fish from surviving in a vernal pool.

 Pennsylvania’s vernal pool indicator animals include:

  • Marbled Salamander (Ambystoma opacum)
  • Spotted Salamander (Ambystoma maculatum)
  • Jefferson Salamander (Ambystoma jeffersonianum)
  • Blue-spotted Salamander (Ambystoma laterale)
  • Wood Frog (Lithobates sylvaticus)
  • Eastern Spadefoot (Scaphiopus holbrooki)
  • Fairy Shrimp (Eubranchipus spp.)
  • Clam Shrimp: Euroamerican clam shrimp (Limnadia lenticularis), diversity clam shrimp (Eulimnadia diversa)

 

Frog eggs in a pool. Photo by Donna L. Long.
Frog eggs in a pool. Photo by Donna L. Long.

The Pennsylvania vernal pools are often in a closed canopy forest dominated by Pin Oaks (Quercus palustris). There may also be mosses present. Some vernal pools don’t have any growing plants. The other plants present tend to be wetland plants. So, if you see a stand of wetland plants (like arums and grasses) but little or no standing water the spot may be a temporary pool.

In spring, I seek out vernal pools to watch and listen to the frogs and try to spot baby salamanders. While walking through the woods or grassy areas you can learn to recognize an eastern vernal pool even in the dry stage. http://www.naturalheritage.state.pa.us/VernalPool_DryPhase.aspx

More information on vernal pools.

Spring Starts from the Ground Up

Sparsely Vegetated Vernal Pool Community
http://www.naturalheritage.state.pa.us/Community.aspx?=30027

What are Playa Lakes?
https://www.americanrivers.org/rivers/discover-your-river/playa-lakes/

Panhandle Playa Lakes
https://tpwd.texas.gov/landwater/land/habitats/high_plains/wetlands/playa.phtml

Prairie Pothole Joint Venture http://ppjv.org/

What are Praire Potholes?
https://www.americanrivers.org/rivers/discover-your-river/prairie-potholes/

2 comments

  1. Well done, Donna! You take a not well-known, and not often written about aspect of the natural world, and write engagingly about it. With good links, and specific information. It would be wonderful if you wrote a bit about the consequences of so much human eradication of vernal pools, and for your Pennsylvania readers, links to pages about the vernal pool indicator species might be helpful. Thanks for writing an helpful us be more alert to the world around us. Great work!

    • Thank you for your encouragement and suggestions. Both are very much appreciated.

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