Vernal Pools: A Forest Nursery
Spring is one of my favorite times to go hiking. Yes, summer is prettier, with the leaves out, and it's a bit more pleasant to have the shade while you are trekking up mountains and through the woods. But there's something special about being in the forest when the world is just waking up from its winter rest. You can see the woods in its naked glory, see what it really looks like under all those leaves. You notice new details, like how not only the leaves of the different types of trees are unique, but the bark as well. It's fun to see the new shoots of plants coming up, and to also see how winter storms affected the forest. You can see fallen branches and trees more easily. And the song of a spring stream...I could listen to it for hours.
My favorite thing to geek out over in the springtime forest, however, are vernal pools.
What's a vernal pool, you ask? Well, vernal means spring, and pool...well, you get the idea. It's a pool of water that exists in the forest in the springtime, and gradually dries up as the summer grows hot. And they are absolutely vital parts of the forest ecosystem. But what makes them special? I mean, there are ponds and streams in the forest as well. There are plenty of other bodies of water. Why do people nerd out so much about vernal pools, and why are there entire scientific organizations out there devoted to preserving them?
Let's have a closer look at what a vernal pool really is. A temporary body of water that dries up eventually over the summer. Then when the winter's snow melts and the spring rains come, the pool forms again, and the cycle continues. What does this cycle suggest could be special about this body of water versus, say, a pond that is always there? If you said, "no fish can live there," you're right!
The fact that there are no fish in a vernal pool is vital. Fish eat things. They eat bugs, plants, eggs of other fish and amphibians, tadpoles, etc. Without fish in the equation, we lose a major predator of creatures such as wood frogs, spotted salamanders, spotted turtles, caddisflies, certain dragonflies, fairy shrimp, and ribbon snakes. The creatures I listed here can ONLY reproduce in vernal pools, where their predators don't live. Wood frogs and spotted salamanders come out on the first warm rainy nights of the spring and travel to the same vernal pools in which they were born the year (or years) before. They lay their eggs in the water, usually on sticks or other debris. And then in three to four weeks, the eggs hatch, and the larvae/tadpoles have to reach maturity before the water dries up in the summer. It's a race against time for them, and they don't always succeed.
For example, in a drier year or a less snowy winter, like this one was in New England, the pools might not form properly or might dry earlier. What happens when a pool dries up before the animals reach maturity? Well...birds and other animals might get a treat, and the rest basically become fertilizer for the forest. Vernal pools are very dependent on weather and climate, and when average global temperatures rise and weather becomes milder on the whole (with extremes in the middle) as seems to be becoming the pattern, some of them dry up forever, leaving species with no where to breed, and they will eventually die out in that area.
Climate change isn't the only threat to vernal pools. When people change the flow of water by developing land, making roads and housing projects, etc, this has an obvious effect on vernal pools. The water doesn't puddle in the same places, if at all. And when people develop land near wetlands, beavers need to find new places to live, and build new dams. These very often flood areas where vernal pools would normally exist, not just in the normal spring way, but making them into permanent ponds (incidentally, this also impacts human life, because sometimes the beaver dams can cause flooding in previously dry areas where houses and shops are, too).
Well, so what? I mean, what's the big deal about a bunch of frogs and salamanders? That's what people said throughout most of history when they saw vernal pools. They thought of them as just big puddles in the woods. But then in the early 1980's, people started paying attention to these pools, and saw what a huge part the creatures that relied on these pools had in the food chain of the forest. If these vernal pools are disrupted, if a forest's habitat is changed enough where they dry up or are flooded forever, everything about the forest changes. Animals and plants will die. Not only that, but the creatures that develop because of vernal pools are important for evolutionary diversity. Diversity in a forest is vital, because the more different species there are, the better chances things survival when natural changes occur. If we have a forest with few species in it and something changes in a way that affects those few species, then poof, the forest dies.
Vernal pools aren't all about the fight for conservation, though that is very important in itself. They can also be a lot of fun. Visiting the pool often over the course of the season, you can watch how frog eggs hatch into tadpoles, and then you can see them grow into frogs. You can find the little "log cabins" that caddisfly larvae build, and if you bring a magnifier, you can scoop water into cups and search for the elusive fairy shrimp. It is a great subject for science fair projects or projects for volunteers at nature sanctuaries to do with college students (you can register your vernal pools for certification to make them protected in many areas. It involves cataloging the species, and this is a GREAT way to get high school and college kids involved). Or you can just share a couple hours with your families at a vernal pool as an activity for a Saturday afternoon.
You don't have to be a scientist or nature conservationist to geek out about vernal pools. But don't be surprised if watching the annual migration of adorable spotted salamanders doesn't inspire you to become one!
For further reading:
The Vernal Pool Association, www.vernalpool.org
Vernal Pools: Natural History and Conservation by Elizabeth Colburn. Very scientific, not really for the average lay reader, but has a ton of information in it. Seriously everything you ever wanted to know about vernal pools.
A Field Guide to the Animals of Vernal Pools by Leo P. Kenney and Matthew R. Burne. Very accessible and has wonderful pictures of creatures found in MA vernal pools.
Search for "vernal pools" on Amazon to find some great picture books for kids. There are way too many to list here, and most of them are great.