We’ve all seen them and thought nothing of it: those temporary spring-flooded areas in forests not yet verdant with the green of summer. While brimming with water in spring, a few short months later they are nothing more than dry, isolated depression on the forest floor. They are as fleeting in our thoughts as they are in the woods.

But such pools are more than just a sign of the changing seasons as winter gives way to spring. These flooded areas, known as vernal pools, are vital if little-understood parts of our woodland ecosystems.

While we’ve come to recognize the role of swamps and marshes in supporting biodiversity and a robust environment, vernal pools – also known as ephemeral pools, intermittent wetlands, or spring wetlands – are still little appreciated and under-protected. That’s unfortunate, believes Emma Horrigan, Conservation Projects and Education Manager for Ontario Nature.

“Most people just think they’re nothing more than puddles, but like all wetlands they are of vital importance,” she says, having spent considerable time studying them. “Though small and temporary, they support a surprisingly diverse range of life.”

The first thing to understand is that vernal pools are hardly random flooding. Instead, they predictably appear in forested areas at the same general time and place in a seasonal rhythm that repeats itself year after year, sometimes for hundreds or even thousands of years.

“Vernal pools can vary greatly in size, from a mere pond to several acres in size. Those in Muskoka are generally on the smaller size – the largest on our properties are 20-30 meters wide – but size doesn’t reflect importance because even a roadside ditch can serve the function of a vernal pool,” explains Aaron Rusak, Administration and Program Coordinator for Muskoka Conservancy. “Generally they are shallow bodies of water, no more than a few feet deep. Crucially, most are located a significant distance away from rivers and streams.”

The cyclical nature of vernal pools, forming in spring and drying out in the summer, means they can’t support fish populations that feast upon eggs and young of a variety of lesser life. In addition, because they are isolated pools away from other bodies of water, predatory species – fish or turtles – can’t easily contaminate them through migration or during periods of flooding. Vernal pools thus represent safe predator-free habitat for many amphibian species for part or part of their life cycles and as a result, like any wetland, they are teaming with life.

“Vernal pools serve as nurseries for a diverse range of amphibian species,” explains Horrigan,“Three salamander species in particular – spotted, blue-spotted, and Jefferson salamanders – depend on vernal pools for breeding, egging, and larval development, as do wood frogs. It’s important to note that Jefferson salamanders are listed as Endangered in Ontario.”

Vernal pools are also vital habitat for fairy shrimp, a small translucent crustacean that feeds on the algae and plankton that accumulates on submerged leaves and twigs, and for a number of shrimp and mollusk species.