VERNAL POOL ECOLOGY
Most of the forested areas in Ohio have some vernal pools. Even where there is steep terrain, a groundwater-fed vernal pool at the base of a slope or near a spring is not unusual. More often, vernal pools are filled by rain and snow melt. The late fall rains and winter snows add to the surface water and raise the ground water. Shallow depressions, with no outlet or channel to carry the water off, can fill with water and incite a riot of biological productivity.
If you are hoping to locate vernal pools, it is best to look from late winter through spring. Once trees are fully leafed out, the water normally disappears. When water is present, you will have the advantage of confirmation through easily observed biological activity. Especially in the earlier weeks of the season, when amphibians are breeding and other biological evidence is easily recognized, vernal pool characteristics are hard to miss. If you hear frogs calling from the woods in March and April, there is a good chance that a vernal pool is near.
One of the key characteristics of a vernal pool is the absence of water during the driest time of year, normally late summer and into fall. At other times of year, when the amphibians have finished their breeding and the tadpoles and salamander larvae have sprouted legs and vacated the pools as the water recedes, you will need to look for other clues. You could find some plants that point you in the right direction. From a distance, clues of a profoundly wet area (even with no standing water) can come in the form of wet-loving bottomland trees like cottonwood, pin oak, swamp white oak, red and silver maples, green ash, and sycamore. Tree trunks in vernal pools can take on a distinct appearance, as they often develop an exaggerated flare or buttress at the base, and these props are often colonized by thick moss with a distinct horizontal upper limit that represents the high water mark. Heavy mosses may also adorn coarse woody debris and fallen trunks since abundance and duration of high water favors these species.
On closer inspection, a shrub layer that includes spicebush, winterberry holly, and buttonbush speak to the high water table and possible seasonal inundation. Should you find an abundance of sedges or skunk cabbage you are tipped off to the presence of very wet soil, often with a groundwater influence.
In the absence of inundation, you can look for the key physical signs that standing water has left behind. The specific topography or gradient of slope can be very difficult to detect. Most vernal pools develop where only inches separate them from the surrounding uplands. Some vernal pools develop a “pit and mound” texture. The unevenness results from plants that love water and build elevation through years of root accumulation, forming tussocks. You may also observe large areas of dark, water-stained leaves in a depression that wetland scientists refer to as a “sparsely vegetated concave surface.” Once the home and hearth of vernal pool denizens, these leaves have been decomposed in water and a relatively low oxygen environment compared with the uplands. A lack of vegetation in these leaf-lined depressions can provide an equally strong indication of the presence of a vernal pool as the plants mentioned above. This forest floor basin may appear to be a sterile and dark wasteland. However, nothing could be further from the truth.
Should one delve deeper, the soils beneath a vernal pool will have hydric or wetland characteristics. The trifecta of wetland designation is hydrology (water), hydric (water adapted) plants, and hydric soils that result over time from the former. For an area to be considered wetland, all three components will be present - and this holds for vernal pools, as they are, after all, wetlands!
Reading the landscape and interpreting the woods is not a skill common to most modern Americans. We will all be richer in character when we better understand the natural wealth around us and participate in its protection and enjoyment. To learn more and hone your vernal pool sleuthing skills, consider participating in one of OWA’s vernal pool discovery days!
If you are hoping to locate vernal pools, it is best to look from late winter through spring. Once trees are fully leafed out, the water normally disappears. When water is present, you will have the advantage of confirmation through easily observed biological activity. Especially in the earlier weeks of the season, when amphibians are breeding and other biological evidence is easily recognized, vernal pool characteristics are hard to miss. If you hear frogs calling from the woods in March and April, there is a good chance that a vernal pool is near.
One of the key characteristics of a vernal pool is the absence of water during the driest time of year, normally late summer and into fall. At other times of year, when the amphibians have finished their breeding and the tadpoles and salamander larvae have sprouted legs and vacated the pools as the water recedes, you will need to look for other clues. You could find some plants that point you in the right direction. From a distance, clues of a profoundly wet area (even with no standing water) can come in the form of wet-loving bottomland trees like cottonwood, pin oak, swamp white oak, red and silver maples, green ash, and sycamore. Tree trunks in vernal pools can take on a distinct appearance, as they often develop an exaggerated flare or buttress at the base, and these props are often colonized by thick moss with a distinct horizontal upper limit that represents the high water mark. Heavy mosses may also adorn coarse woody debris and fallen trunks since abundance and duration of high water favors these species.
On closer inspection, a shrub layer that includes spicebush, winterberry holly, and buttonbush speak to the high water table and possible seasonal inundation. Should you find an abundance of sedges or skunk cabbage you are tipped off to the presence of very wet soil, often with a groundwater influence.
In the absence of inundation, you can look for the key physical signs that standing water has left behind. The specific topography or gradient of slope can be very difficult to detect. Most vernal pools develop where only inches separate them from the surrounding uplands. Some vernal pools develop a “pit and mound” texture. The unevenness results from plants that love water and build elevation through years of root accumulation, forming tussocks. You may also observe large areas of dark, water-stained leaves in a depression that wetland scientists refer to as a “sparsely vegetated concave surface.” Once the home and hearth of vernal pool denizens, these leaves have been decomposed in water and a relatively low oxygen environment compared with the uplands. A lack of vegetation in these leaf-lined depressions can provide an equally strong indication of the presence of a vernal pool as the plants mentioned above. This forest floor basin may appear to be a sterile and dark wasteland. However, nothing could be further from the truth.
Should one delve deeper, the soils beneath a vernal pool will have hydric or wetland characteristics. The trifecta of wetland designation is hydrology (water), hydric (water adapted) plants, and hydric soils that result over time from the former. For an area to be considered wetland, all three components will be present - and this holds for vernal pools, as they are, after all, wetlands!
Reading the landscape and interpreting the woods is not a skill common to most modern Americans. We will all be richer in character when we better understand the natural wealth around us and participate in its protection and enjoyment. To learn more and hone your vernal pool sleuthing skills, consider participating in one of OWA’s vernal pool discovery days!
