Signs of Spring 10: Vernal Pools (and more!)

H. crucifer Photo by USGS (Public Domain)

Spring frogs are important harbingers of the season in Western Pennsylvania, and Deborah and I listen for them carefully. The Spring Peepers (Hyla crucifer) are usually the first frogs to make their presence known. They begin their soft, peeping group choruses in and around small ponds and wetlands as soon as there are some warm, spring evenings. This year, however, we didn’t hear any peepers out in the usual places around our home.  This past winter’s lack of snow fall (leading to a low level of spring snow melt) and our very dry March and April may have cut into available water habitats for these little frogs to use as mating sites.

Gray tree frogs (Hyla versicolor) typically start their resonating trills soon after the peepers. This year we did hear some tree frogs out around our house in spite of absence of peepers, but their numbers and volumes were greatly reduced from previous years.  In some years the tree frogs continue to trill well into the summer. We’ll see if they can re-group or gather new strength.

There is a third frog that we regularly look for in this winter-to-spring transition: the wood frog (Rana sylvatica). We have to drive some distance, though, in order to see and hear wood frogs because they don’t do well in areas that have too many people.  They need dense, quiet woodlands with lots of leaves to hide under and lots of low spots for their spring mating pools!

Photo by D. Sillman

So, Deborah and I drove down to Ohiopyle last weekend and met up with Rob and Michele for our annual, spring hike around Ferncliff Peninsula. We were looking for any new (or different) signs of spring, but in particular we wanted to see if we could find the wood frogs that were so abundant here three years ago (on a warm afternoon hike in late March 2013). The timing of the emergence of the wood frogs from hibernation and their frenetic mating in the temporary, spring (or “vernal”) pools of water (accompanied not by trilling or peeping but by a call that sounds like the quacking of a duck!) are all influenced by air temperatures and the abundance of surface water. Because of our very non-typical winter and spring, we were curious if there would be any amphibians at all! Also, incompletely filled pools might dry out before the aquatic larvae of the breeding amphibians have had sufficient time to develop legs and lungs. This disastrous outcome could wipe out an entire year’s crop of young amphibians.

Photo by D. Sillman

We walked out onto the Ferncliff Peninsula at Ohiopyle. The day was getting warm, and it felt good when the sun finally came out from behind the clouds. The first part of the hike was over the far shore’s rocks and boulders along the Youghiogheny River at the Ohiopyle Falls. There was quite a bit of new flood debris along the shore, but Rob commented that the water level seemed lower than usual and the river rocks seemed more exposed and extensive than in previous years. Possibly in response to our near-drought more water is being held back behind the Youghiogheny Dam.

The isolated pools up and around the shoreline rocks, though, were full of life. Hundreds of tiny, black tadpoles were clustered together in the sunlit sections of the pool. Water striders were whirling and skimming across the still water and were actively bouncing into each other (establishing territories or mating?) and searching for food.  There were several types of eggs in the pool including the very distinctive cloudy and opaque eggs masses of the spotted salamander. Rob saw a small, brown salamander hiding in the brown leaves at the bottom of one of the pools. He poked it with the tip of his hiking stick (very gently!) and it swam to the back of the pool and buried itself in the leaves.

Red Trillium Photo by D. Sillman

The trail climbed up away from the rocks and headed out along one side of the peninsula. The red maples and yellow poplars were all just starting to leaf out. They were covered with light green halos of tiny leaves. The abundant hemlocks and the scattered white pines made dark, bordering lines of green around the spindly hardwoods, and thick bunches of rhododendron bushes added their waxy deep greens to the landscape. The greens stood out sharply against the overwhelming brown ground cover of scattered, dead leaves. We also saw some spring wildflowers: red trillium, sessile leafed bellwort, and star chickweed (all pictured above and below).

Sessile leafed bellwort Photo by D. Sillman

Every time we hike this trail something happens to separate Deborah and Michele (who inevitably walk out ahead at a rapid pace) from Rob and I (who lumber along at our slow (but steady!) pace). When we made the big turn in the trail after inching along a narrow rock side trail that ran along a steep drop to the river, we got a glimpse of two people walking up and over a trail that ran up to the top of the peninsula. We thought that Michele and Deborah had taken the turn to go up, so we did too. Unfortunately we realized (after fifteen minutes or so of scrambling up the rocky trail) that the people we were following were not Michele and Deborah. We hope that they didn’t notice that we were stalking them!

We cut back down to the lower Ferncliff Trail, but by then were hopelessly separated from Deborah and Michele. Rob’s cell phone died in mid-text “where are…?” and so we plodded on following a couple and

Star chickweed Photo by D. Sillman

their three little girls trying not to fall too far behind them!  Rob and I continued on the Ferncliff Trail and eventually re-made contact with Deborah and Michele near the trail’s end parking lot.

The Ferncliff Trail connects to the Great Allegheny Passage Trail. This is where we had seen the series of vernal pools full of wood frogs back in 2013. We checked them out very hopefully but were very disappointed by the water levels and quality. The pools were about half of their widths and depths of three years ago and were choked with algae and sediment and bits of litter and tossed debris. We saw neither frogs nor any egg masses nor any tadpoles. I don’t think that it will be a good year for amphibians in Western Pennsylvania!

Vernal pools are an important part of the forest habitats throughout the Eastern United States. They are small, shallow bodies of water with fluctuating water levels. Typically, these pools attain their maximum depths and volumes in the spring and their minimum depths and volumes in the summer. Many of these pools completely dry up especially in drought years or years of meager snow fall (like 2016!). A vernal pool must, according to Elizabeth Colburn in her excellent book Vernal Pools: Natural History and Conservation (2014), stay flooded for two or three continuous months, so it is, indeed, something more than just a rain puddle.

Vernal pools have no continuous inflows or outflows. They exist as isolated basins in the midst of their woodland ecosystems. This disconnection to streams and the possibility (or, more appropriately, the probability) of drying out generates a critical ecological feature of these pools: they do not have fish. And, this distinctive absence generates an aquatic habitat especially conducive to the development of a wide variety of amphibians whose eggs and immature life stages are heavily preyed upon by many fish species.

Vernal pools are greatly affected by the types and densities of the trees that surround them.  The chemical nature of the prevailing leaf species influences the acidity, turbidity and nutrient levels of the pool waters.  The history of a pool and the regularity and predictability of its occurrence and duration also has profound influences on the diversity and abundance of its breeding amphibians.

These pools in the Ohiopyle forests have been in place for many years and rely on sufficient melt and spring rain to fill them sufficiently. Let’s hope that next winter is a bit more snowy and that the March and April rains are more abundant. We need to hear ALL of the spring frogs next year!