March of mound ants is Rx for Maryland savanna

Mounds built by Allegheny ants signal recovery of a rare savanna in Baltimore County, Maryland.
BALTIMORE COUNTY—To an amateur archaeologist, the humped hillocks dotting the stretch of fallow pastureland might look like the remnants of burial rituals abandoned long ago by a civilization of Lilliputians.

But any ecologist familiar with this recovering serpentine landscape near Baltimore knows better. These emerging bumps signify the resilience of Allegheny mound ants. Armies of these tenacious insects are reclaiming their former home territory on this unusual savanna.

Why now? In a nutshell, the ants’ mantra seems to be “follow the Indian grass.”

That native grass species is beginning to prosper again after being crowded out on this section of serpentine by tenacious grasses more fit for foraging livestock and invasive tree species such as Virginia pine and red cedar.

The ants have come marching back one by one as naturalists with the Maryland Natural Heritage Program and volunteers spent part of the last several years cutting and clearing those non-native trees from a six-acre patch of the almost 2,000-acre Soldiers Delight Natural Environment Area.

“That section was so degraded from agricultural uses that we weren’t even going to bother with it,” state restoration ecologist Wayne Tyndall told Renewal News about the parcel he and others had written off as being unworthy of an investment of time and elbow grease. “Only recently, with the re-emergence of the Indian grass, did we decide to take another look at the science and reconsider.”

The tiny ants are admirably diligent, constructing dirt mounds as small as footstools and as large as couches. And their homes, which include intricate chambers, galleries, tunnels and deep “basement” incubators are remarkably engineered for feeding and breeding.

For instance, the ants site their rounded shelters to maximize southern exposure. They “mow” and “herbicide” with formic acid rooftop grasses to expose more dark dirt and maximize the sun’s heating capacity.

Over centuries, the ants have sustained a symbiotic relationship with two types of wildflowers, serpentine chickweed and lyre-leaved rock cress, which both have white blooms. Interestingly, the ants deliberately cultivate both native plants to attract butterflies and moths such as the hummingbird-like sphinx moth seeking flowering stems and leaves to lay their eggs.

The ants score on several levels, scientists say. For one, they harvest those eggs to rear the ensuing caterpillars as a food supply. The ants also tunnel to the plants’ roots to feast on “leaking” sugars and proteins, in addition to nearby mycorrhizal fungi. They also likely harvest the seeds after the plants reproduce.

In tandem, the white wildflowers benefit from superb growing conditions and cross-pollination.

Up until the 1730s, the Susquehannock were among the Native Americans that had kept the Maryland serpentine intact by fire-hunting in autumn to flush game. While newly arrived white settlers mimicked that fire cycle for at least five decades, researchers have determined that the newcomers eventually preferred spring burns because earlier fires jump-started lush vegetation.

Early on, settlers tested several types of livestock on what they referred to as “the barrens,” but resorted to grazing mainly cattle into the 1930s because they proved to be the most “wolf-proof.”

Intensive grazing by non-native farm animals, combined with plowing and planting of hayfields well after 1900, is a textbook example of how modern agriculture transformed a native savanna into an artificial grassland of non-native plants.

Plowing and planting of those persistent hayfield grasses was good for cows but gloomy for indigenous species such as Indian grass, which was outcompeted because it germinates in the summer and peaks in the fall.

All of those bovine mouths and hooves – as well as the eventual drop-off of any fire regime at all — also took their toll on the serpentine’s native plants, which already faced severe challenges adapting to thin, nutrient-poor soil with an odd chemistry.

Magnesium silicate in the underlying bedrock gives much of the serpentine soil a greenish hue. Varying mixes of iron, chromite and magnesium make for darker dirt.

Soldiers Delight, home to several dozen threatened plant species, is one of the remaining remnants of the band of serpentine savannas that once stretched from Alabama to Canada.

In the mid-1990s, Maryland returned a fire regime to the preserve in the form of controlled burns managed by trained crews. Doses of fire are just one form of environmental medicine being prescribed to help restore this ecological gem to wholeness.

Two species of oak, post and blackjack, are naturally dominant on the preserve. And they’ve also had more room to flourish as the pines and cedars are culled.

Tyndall, who has played a crucial role in resuscitating the preserve, has delved into scientific studies as well as the meticulous research of William B. Marye, a prominent authority on Maryland history, genealogy, topography, and Indian archaeology who lived from 1886 to 1979.

The reappearance of Indian grass and mound ants in that corner of Soldiers Delight once deemed unsalvageable, gives ecologists hope that little bluestem, gray goldenrod, purplish three awn, grass-leaved blazing star and other native serpentine plants will follow suit.

Tyndall is thrilled with the resilience and resurgence of a long-dormant seed bank.

“Indian grass is a very, very competitive species, so I think that is why we are seeing it reemerge first,” he said. “We should start seeing more of the others in coming years.”


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