On a sunny autumn afternoon in late October, more than a dozen volunteers from nonprofits Natural Lands and Tyler Arboretum joined forces to collect native plant seeds at Willisbrook Preserve, owned and managed by Natural Lands. The seeds will be propagated at Tyler Arboretum, and then planted at both Tyler’s Pink Hill and Natural Lands’ Willisbrook Preserve as part of a joint effort to re-introduce rare species of local genotypes to this serpentine barrens habitat.

The serpentine barrens at Willisbrook Preserve, located in Malvern, are among just a handful of remaining serpentine grasslands in the eastern U.S. Serpentine barrens contain serpentinite, a type of rare greenish bedrock from which the soils are weathered. The soils’ chemical characteristics — high in magnesium and nickel and low in calcium — make them inhospitable to most plants. In fact, the term “barrens” was coined by farmers who noticed crops would not grow there.

However, a few tenacious plant species have adapted to these extreme soil conditions. Many of these plants are rare, threatened, or endangered, as are some of the animals that make the grassy habitat their home. Without the barrens, these native plants and animals could be lost.

The three-acre meadow known as Pink Hill, located at Tyler Arboretum in Media, was named for the candy-colored Phlox subulata that blooms there every spring. Like those at Willisbrook Preserve, the soils at Pink Hill are also underlain with serpentinite. The horticulture staff at Tyler want to augment the existing plant species growing there. By collecting and propagating seeds from nearby Willisbrook Preserve, plants added to the barrens will have the same local genotype.

“The serpentine barrens ecosystem has much more in common with Midwest grasslands than with the forest vegetation that prevails here in the East,” said Dr. Roger Latham, ecologist and conservation biologist. “These two barrens are home to a fantastically diverse group of plants and animals, including several that are rare or endangered.”

Ironically, much of the loss of serpentine grasslands is due to inattention from humans. In our year-round moist climate, grasslands rely on periodic disturbance to prevent woodlands from overtaking them. For millions of years, this essential disturbance came from native animals. Mastodons, mammoths, and herds of hungry elk kept trees at bay by browsing and trampling the ground beneath them.

Grassland-sustaining disturbance was continued by indigenous peoples setting fires and later by livestock grazing and mining. Today, in the absence of these activities, bordering woodlands quickly encroach, creating their own rich soil layer over the inhospitable serpentinite as their leaves drop and decompose.

“We’re delighted to be working with Tyler Arboretum on this important partnership effort to bolster the population of some rare barrens’ plants,” said Oliver Bass, president of Natural Lands. “Grasslands like those at Tyler and Willisbrook are living ecological relics that are worthy of our preservation and stewardship efforts.”

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