The Barrens, an increasingly rare habitat-type found in our region, reminds us that life started and evolved in a heavy metal environment. To appreciate these unique geoecological communities you have to start with the chemical composition of the serpentine belt that cuts an arc across the Mid-Atlantic. The presence of serpentine, a hydrothermally formed rock that once oozed as magma from canyons deep in the ocean floor, signals a hostile growing environment when it is found at the surface. Known for its seafoam green color when polished (i.e. foot traffic, vehicle tires, buffing), the ore chromite was important in steel and iron-making and was heavily mined from the 1830s through the early 1900s. Road and place names still carry the heritage of quarrying as Rocks Chrome Hill Road (Harford County, Maryland), Bald Hill Road (Baltimore County, Maryland), Barrens Road (York County, Pennsylvania), Chrome Mine Road (Lancaster County, Pennsylvania) and many others.
|Polished serpentine on footpath - Willisbrooke Preserve, Chester County PA|
The story of this landscape starts as much of the region's geological history does, during the Paleozoic Era. Some 500 to 250 million years ago, ocean sediments, volcanic islands, and ultramafic crusts (that ooozy stuff gone solid) was squeezed together as accreted terranes (parts of other land masses) and thrust onto the North American continental plate by the great migration of the North Africa. Imagine layers of sodden leaves packed tight against a midstream boulder - layer upon layer of tilted ocean beds, compressed islands, flattened vertical pillows of lava, welded seams of sediment end on end, and the mantel crust itself pushed up and over an unyielding plate. Where the layers of raw ocean bottom stand vertically exposed at the surface they look a lot like this:
|Weathered serpentine ridge - Willisbrook Preserve.|
The chemical composition of serpentine is a combination of magnesium, chromium, iron, and nickle - heavy metals and toxic! These are the components of Earth's deep interior that have come to the surface very different than other types of igneous or continental crusts! The resulting soils are very low in calcium and other minerals important to plant life. The most tolerant lichens and mosses introduce basic biomechanical processes that slowly weather the rock and here a thin layer of nutrient and moisture-holding humus accumulates.
|Thin soils over gravel - Goat Hill Serpentine Barrens, Lancaster County, PA|
|Exposed cliff outcrop near the old chromite mine - Goat Hill.|
Serpentine soils do not hold moisture well. Outcrops and barrens occur on steep land, atop high, sun-scorched ridges. Thin soils are more like those found in desert environments. Endemic plant communities that form in these places are strictly contained by the boundaries of the serpentine exposure. The most plant diversity occurs in pockets of soil accumulation and in shady areas that hold precious moisture. The rarest of plants occur where conditions exclude all others. Those that thrive do so on inhospitable ground. There is a lesson here in the evolution of life in a toxic environment, like the environment we've created out of heavy manufacturing and industry over the course of the Industrial Revolution. Heavy metal soils are found downwind of industrial centers, dump sites, and brown fields of manufacturing plants along the Eastern seaboard. I wonder what a serpentine barrens can teach about reclaiming soils for a less toxic life?
|A tuft of Bryum moss holds morning dew - Goat Hill.|
|Pixie cup lichen holds rain droplets and dew in its upturned bowls - Goat Hill.|
I examined collections of moss and lichen and noted that oak and sassafras leaves from distant woods had blown across the savannah and were caught in tangle of pine needles and fallen twigs. The simple process of blowing wind imports vegetative matter, dirt, and dust needed to start the process of forming a duff layer. When enough of a stable surface has built up grasses will germinate and take root. It may take centuries for enough organic matter to build under a living layer of grass and moss before pines and bear oak can establish. The forests in most protected barrens are over a hundred years old but may only be twenty feet high!
|Gravels and distinct soil zones that favor grasses then trees - Goat Hill.|
The savannahs of the barrens served indigenous people well. Susquehannock and Lenne Lenape hunted large grazing animals on these grasslands: bison, elk, deer. Early hunters learned to manage the savannahs for ultimate productivity by burning the barrens every few years to kill off intruding forest and scrub and to encourage fresh new grasses favored by big game. Whether fires caused by lightening or managed by man, this process is essential to barrens ecology even now. Today the Nature Conservancy, Natural Lands Trust, and Pennsylvania State Forests management in the WIlliam Penn Forest section include control burns in cyclical applications. The only thing we are missing are the large herbivores!
Can you imagine when large parts of Maryland and Pennsylvania existed as lush grasslands? I can picture how beautiful it must have been! Though the barrens landscape is but one type of Eastern prairie, the whole classification of native grassland in our area is considered endangered under threat from suburban sprawl and highway expansion. What developer doesn't love a treeless plain on which to build the next mega-mansion neighborhood? Sally and I gawked as a new 'carriage home' community was being built right up to the edge of the Willisbrook Barrens Preserve. Surrounded by sprawl, conservation and land trust groups scramble to save these places from development.
|Indian Grass, Willisbrook Preserve.|
|Dropseed Grass, Willisbrook Preserve.|
At Goat Hill Preserve, William Penn State Forest, Lancaster County, survey flags are found along the trails - please don't remove them. Rutgers researchers are looking how shifts in ecological communities occur over time as soils build and improve, and as plant communities colonize and migrate. All living things require metals for metabolism and evolution has provided ways to balance this with the possibility of toxic overload, especially in those plants that tolerate these soils.
|The Rose Trail start at the Goat Hill parking lot.|
What is interesting about plant studies on inhospitable land is that heavy metals in our atmosphere, emitted by coal burning power plants, a century of historic heavy industrial steel industry, vehicle and manufacturing plant emissions, all eventually end up in our soils. This forces ecological communities to quickly adapt or perish. What we are learning from the barrens may help us with bioremediation strategies that address toxic industrial sites including the use of moss and lichen soil builders and tolerant plant communities. It looks like lichens, mosses, and grasses save the day!
|Research site, Goat Hill Barrens.|
The evolutionary responses of plants to a toxic environment include complex interactions within biogeochemical community networks. What we know about the serpentine barrens is that, realistically, conditions should be so severe here that it might just as well be desert. But it isn't. So our curiosity is piqued and we begin to ask questions. At the level of genes, mutation, and adaptation, complex responses change the trajectory of an organism's ability to thrive or die. As I walked around this achingly beautiful grassland with Sally at Willisbrook Preserve on Saturday, and by myself at Goat Hill on Sunday, I couldn't help but ask questions that have everything to do with our own survival in a world we've made hostile by our own doings:
|Maiden Hair Fern on the edge of a grassland community.|
- Is there a contemporary proxy for environmental adaption to human-induced heavy metal pollution?
- What can life's ancient and exquisite ability to form protective systems teach us about enhancing our own prospects for survival?
- How do mammals and birds intersect and interact with disconnected grasslands communities in our region?
- Will it ever be possible to reintroduce large grazing animals like elk (that are doing fine in North Central PA, thank you!) into some of our larger barrens landscapes? What would the trophic cascade look like if elk were re-introduced?
|Bushy aster is a rare blue flowered serpentine plant, Goat Hill.|
|Serpentine aster, another rarity, is abundant at both sites.|
|A tiny mustard flower in a brown and parched section.|
I don't think it's a matter of biomicry, to simply copy what another species is doing to survive, but a question of restoring relationship to other species from bacteria to bald eagles and beyond. The world of the serpentine barrens teaches us about the processes of biological community evolution, some important lessons in a world where we are just waking up to the idea that, as Leopold said, we are part of landscape community.
|The start of a grassland - marked for migration survey.|
Goat Hill Preserve is closed from October to January for hunting season.
There are several conservation lands that feature or include serpentine barrens in our area. You might be surprised, however, at how development and the pressures of other types of land use have surrounded them.
The Natural Lands Trust - Willisbrook Preserve, Malvern, PA
Friends of the Stateline Serpentine Barrens oversees a broad expanse of serpentine barrens, working towards a connective sanctuary concept of interrelated sites. They maintain an index of published papers regarding flora, fauna, paleoclimate, and geology on this site.
Emily Monosson, PhD has written an incredible book for us science and natural history geeks interested in evolutionary response to hostile environments. Evolution in a Toxic World: How Life Responds to Chemical Threats (2013).
Fact sheet on the Serpentine Aster, Symphyotrichum depauperatum