Crews thin trees at Mark Twain Lake to help 200,000 endangered Indiana bats

Every autumn, Missouri’s Mark Twain Lake undergoes a unique clearing process to support one of North America’s most endangered bat species. Around 200,000 Indiana bats rely on the forested areas surrounding the lake during the warmer months and migrate east to hibernate at Sodalis Nature Preserve near Hannibal, accounting for roughly one-third of the species’ entire North American population.

The U.S. Army Corps of Engineers, in collaboration with The Conservation Fund, has initiated forest stand improvement work at public wildlife management areas near Mark Twain Lake. The project aims to reopen flight and foraging corridors that have become crowded due to decades of insufficient timber management.

Shade-tolerant tree species, such as sugar maple and ironwood, have dominated the forest’s middle canopy over the past four decades. While these trees contribute to a healthy woodland ecosystem, their dense growth can obstruct sunlight and create obstacles for bats moving between feeding areas and roost trees.

Instead of clearing large sections of forest, crews employ a targeted technique called hack and squirt. Workers make small cuts around the trunks of chosen trees and inject herbicide into those openings. This method enables crews to selectively remove trees while preserving the overall forest structure.

An interesting consequence of this approach is the creation of bat habitat from dead trees. Once the targeted trees perish, they are allowed to remain standing and gradually transform into snags. Indiana bats rely on mature trees with cracks, crevices, and peeling bark for roosting, particularly in the overstory oaks scattered throughout the area. Depending on the tree, a treated snag can provide valuable habitat for four to ten years before naturally decomposing.

These treatments are conducted in late summer and early autumn when trees begin transferring nutrients and stored energy to their roots in anticipation of winter, facilitating better herbicide penetration.

The primary objective of the habitat restoration is to benefit Indiana bats. By clearing the middle layer of the forest, sunlight can penetrate the understory, promoting native grasses, flowering plants, and young oak-hickory growth. These changes can enhance habitat conditions for various wildlife species, including deer, wild turkey, and others that depend on the forest understory.

Last year, an initial 30-acre phase of the project was successfully completed. Forestry crews are now progressing toward treating over 250 acres around Mark Twain Lake by November 1. Wildlife management areas remain accessible to hikers, hunters, and other visitors throughout the work. It is requested that visitors maintain a safe distance from forestry crews as habitat restoration continues.