Habitat description
Caves are natural voids occurring in bedrock. Solutional caverns occur in calcareous rocks, like limestone or marble, but fracture and talus caves can occur in any rock. Sinkholes, sinking streams, caverns, and springs occur in landscapes with extensive calcareous rock formations, sometimes known as karst. Water flows through cracks, sinkholes, and other subterranean openings in karst and reappears on the surface via springs and seeps. Springs emerging from karst provide cold (5°-8°C) water recharge into streams, enhancing coldwater fisheries habitat. Although they are human-made, mines can also provide some of the same habitat features as natural caves. There are more than 70 documented caverns in Massachusetts and an unknown number of caves.
Characteristic plants and animals
Larger mines and some caves are particularly important for hibernating bats. Except for the big brown bat (Eptesicus fuscus), all bats that hibernate in Massachusetts have been listed under the state Endangered Species Act because of the steep declines in hibernating bat numbers due to White Nose Syndrome, and the persistent threat of disease. Taconic cave amphipod and piedmont groundwater amphipod depend on cavernous features for their primary habitat and are exceedingly rare in Massachusetts. Many common mammals use caves for denning sites and eastern phoebes build nests on the vertical outer walls of caves.
Except for regular bat hibernacula surveys, Massachusetts caves, caverns, and springs are under-surveyed, despite great potential for supporting undescribed endemic animals or other rare species.
Associated habitat types
Ecological processes
The development of solutional caverns is a slow geological process, typically requiring extensive periods to form significant cave systems. Solutional caverns are formed when carbonate rocks dissolve in the bedrock, creating indents, openings, and passageways within the earth. Rainwater picks up carbon dioxide from the air, percolates through the soil, and turns into a weak acid. This slowly dissolves out the rock along the joints, bedding planes and fractures, some of which become large enough to form caverns. In Massachusetts, the upper levels of caverns were scoured away by the glaciers or the glacial ice cover suppressed the limestone solution process. As a result, Massachusetts caverns are small and young in development. None are large enough to support large numbers of wintering bats. Although some caves in Vermont and New York do support large bat hibernacula, in Massachusetts several mines provide much larger spaces and better conditions for wintering bats.
Threats
- Development is the primary threat to this habitat. Caves, underground passages, and water conduits may be filled in or destroyed as homes and roads are built. Some cave and mine entrances are filled in or blocked by landowners concerned about liability.
- Excessive withdrawal from aquifers (natural systems modification) can lower water tables, causing caverns to collapse, drying of springs, and a loss of biodiversity. Due to a limited amount of filtering, contaminants from septic systems, lawns, and farms can easily pollute the water in karst systems.
- Visitation for recreation or tourism during times when bats are hibernating (October to early May) can cause bats to wake and burn fat stores, which can lead to illness and death (human disturbance).
- Climate change is increasing the frequency and severity of extreme weather events such as floods and droughts, shifting precipitation patterns, and raising summer temperatures. Changes like these may threaten the stability of habitats, cause stress to vulnerable species, and alter cave formations (like stalactites and stalagmites) that take hundreds of years to create.
Conservation actions
- Proactive habitat protection: Protect land around springs, caves, and mines supporting state-listed animals and other SGCN.
- Habitat restoration and management: See recommendations below.
- Law and policy: Regulate and limit the impacts of development, gravel mining, pollutants, and water withdrawals on springs, caves, and mines used by state-listed animals and other SGCN.
- Conservation planning: Produce conservation and recovery plans for bats and other SGCN. Include caves and karsts in conservation planning efforts at multiple spatial scales. (See BioMap as an example.)
- Surveys, monitoring, and research: Conduct updated surveys of documented sites for rare spring, cave, and mine animals, and survey nearby suitable habitat. Continue repeat survey efforts of important bat hibernacula on a regular schedule to determine the use and species composition of hibernacula across the state, and the infection intensity of WNS.
- Public outreach and education: Educate state residents about the ecological benefits of bats. Educate and inform the public about the values of spring, cave, and mine habitats for biodiversity and water resource conservation, and threats, through agency publications and other public outreach. Installing sensors to measure changes in hydrology, CO2 levels, and structural stability can help the public understand the status of a Cave habitat and take action to preserve it. Provide decontamination protocols and requirements for recreational caving, and work with the caving community to minimize spread of disease between sites (National White-Nose Syndrome Decontamination Protocol 2012). Continue to work with the USFWS and other partners involved in reducing the spread of WNS in North America through education, research, and management.
Restoration & management recommendations
Before undertaking a restoration or management project, it is important to establish clear goals that are compatible with site conditions. Factors to consider include identifying the resources required for restoration and long-term maintenance, and securing community, stakeholder, and institutional support. For more information, see habitat management priorities and planning.
- Access control: Caves and mines that receive winter visitation from humans should be gated and closed to the public during hibernation in a way that prevents human disturbances while still allowing bats and other animals to enter.
- Cave restoration: Entrances that have been filled in or collapsed can be reopened.
- Water quality and quantity restoration: Encourage communities surrounding vulnerable caves and karst to use good practices when maintaining their septic systems, using chemicals on their lawns, and using fertilizers on their crops. This will reduce contaminated runoff from entering the cave and karst systems and impacting vulnerable species.