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MORE THAN JUST A PUDDLE: Audubon Monitors Critical Woodland Vernal Pools
By Dr. Scott Ruhren, Senior Director of Conservation
In forests across Rhode Island there are temporary wetlands teeming with life in the spring. Woodlands echo with the trilling calls of spring peepers, the “quacking” of wood frogs and later, the calls of American toads. These forest amphibian hotspots are vernal pools, sometimes referred to as temporary woodland pools or seasonally wet pools. Most are temporary, but some larger pools do not entirely dry out.
Many vernal pools are believed to have formed by glaciation. Despite minor regional differences and terminology, scientists agree that vital traits link these pools: a woodland setting, shallow pools that dry up annually or every couple of years, and a list of indicator species that include wood frogs, spotted salamanders, and fairy shrimp. Importantly, the list also includes the absence of any fish species. Fish would consume the developing amphibians, destroying the vernal pool food web. Reptiles and many invertebrates including snails and insects also reproduce in Rhode Island’s vernal pools.
Unlike toads and spring peepers which are more flexible in their habitat requirements, wood frogs and spotted salamanders depend on these temporary wetlands. These vernal pool obligate species complete their development in just a couple months before pools dry. The less common marbled salamanders visit dried pools in late August to lay eggs that hatch when the pools refill from late-season rain.
Habitat change and forest clearing can mean the end of vernal pools both physically and functionally. Exposed pools get too warm and may even evaporate long before any amphibians could reproduce. Dead, dry eggs and tadpoles are evidence of this. Because of their sensitive physiologies and porous skin, eggs, larvae and emerging adults are vulnerable to environmental stresses such as pesticides, heavy metal pollution—sometimes from road runoff—acidification from rain and introduced fungal and viral diseases. This sobering list of threats to the forest ecosystem is rationale to monitor the pools.
Audubon monitors these special habitats to determine how well they are functioning and to add to a statewide database and mapping effort coordinated by the Rhode Island Natural History Survey (RINHS). This year, Audubon staff, TerraCorps members, and volunteers monitored 16 pools within Audubon wildlife refuges. Using a standard protocol developed by several partner conservation groups, the team of monitors recorded physical features of each pool including area, water depth, and GPS coordinates. They also tabulated the presence and numbers of egg masses, amphibian larvae, and other community features. The data is both shared with RINHS and used to influence forest management practices at Audubon.
The impacts of climate change on vernal pools are still being assessed, but it is obvious that when there is less snow, or very warm spring weather, pools do not last as long and can impact the reproductive success of woodland amphibians. For protection, Audubon is careful to minimize human activities around vernal pools and divert trails away from these wetlands. They are not merely big puddles in the woods, but vital and vulnerable habitat needing perpetual protection.
