Serpentine soils are anything but barren: They support a unique grassland habitat

I have never been to the African grasslands, where lions, zebras, elephants, and wildebeests seem to be in continuous danger. I have, however, been to a Maryland habitat that few people know about, and that, even though lion-, zebra-, elephant- and wildebeest-less, reminded me strongly of those African savannas.

This habitat I am talking about is the Serpentine Grasslands (or Barrens) of the Eastern United States. If you have never heard of them, fear not! Hopefully, by the end of today’s post, you will know a bit more about them and you’ll even try to go visit the few remains that still exist of this beautiful but endangered habitat of our region.

Serpentine Barren Grassland
Fig. 1 – The Serpentine Grasslands of Maryland at Soldiers Delight. Photo: U. Weber.

As you may have guessed from its name, Serpentine Grasslands or Barrens are prairies where the dominant plants are grasses. This is all good, but if they are grasslands, why are they also called Barrens, you may be asking yourself. The answer to that question is what in my opinion makes these habitats so fascinating; something that is also hidden in the other part of their name: “Serpentine”. Indeed, the word Serpentine refers to the type of soil these grasslands are on.

Serpentine soils form on a type of bedrock called serpentinite. This type of rock only exists in places where tectonic plates come into contact, fold, and volcanic activity occurs. This happened in our area about 480 million years ago when the Appalachian Mountains formed. Because of this, there is now an arc of serpentinite present in the Maryland-Pennsylvania area, parallel to the mountains.

Serpentine Soil
Fig. 2 – The Serpentine Grasslands have usually bare soils that have a greenish tint, due to the serpentinite they originate from. Photo: A. Espíndola.

Serpentinites are rich in many metals and other compounds that make the soils that form on top of them relatively toxic and unfriendly to many plants. Because not many plants can grow on these soils, not much soil is retained and the ground ends up being rocky. Because of this characteristic, places with these soils are not very fertile, and, when the Europeans arrived in the area, they started referring to them as ‘barren’, since they were not only infertile, they also had no timber on them. However, even though they were referred to as barrens, many plants do grow on these thin soils, and actually, many of Maryland’s rare flower plants and grasses are adapted to grow in this habitat!

Indeed, the Serpentine Grasslands of Maryland and Pennsylvania are some of the unique places where it is possible to find, for example, the rare moss pink, serpentine aster, or the sandplain gerardia (Fig. 3). It is also home to several endangered and rare species of butterflies and moths such as the Dusted or the Cobweb Skipper (Fig. 4).

Even though the plants and butterflies present in this habitat are relatively well-studied, we still know very little about what other organisms live in the grasslands. To remediate this, in my lab at the University of Maryland in College Park, we are working on trying to understand better what species of insects are present in the area.

Plants of the Serpentine Barron
Fig. 3 – Many rare plants are present in the Serpentine Grasslands of the Eastern US. For example, the moss pink (left; Photo: J. Gallagher) and the sandplain gerardia (right; Photo: A. Espíndola).

For the moment, we are focusing on insect pollinators, and our first works indicate that the plants growing in these grasslands are pollinated not only by bees but also by hoverflies, showing how important these lesser-known pollinators may be to sustaining a very rare habitat of our region. (Take a look here to learn more about hoverflies as pollinators.

The Serpentine Grasslands had not always been rare and endangered. Indeed, serpentine soils extended for quite an area in the Maryland-Pennsylvania region. So, what happened to this habitat that made it so rare today? Ecologists and historians can help us with this.

Like many habitats dominated by grasses, Serpentine Grasslands need fire to sustain themselves. In the absence of fire, pines and red cedars from the surrounding areas start establishing in the grasslands and compete with the grasses and all the rare plants, making the once grassland become an encroached pine forest. When the Europeans first arrived in our region, documents said that there were Serpentine Grasslands that extended for at least 130,000 acres. Today, Serpentine Grasslands occupy about 1.6% of that area.

These grasslands were managed as hunting grounds by several tribes (Susquehannock, Shawnees, Lenape Delaware), who burned them regularly to maintain the grasses and attract large herbivores to hunt. These tribes had complex systems of rights over these lands, which they shared with neighboring tribes as needed. Records show that these extensive grasslands were extremely rich in fauna. There were a myriad of birds (mentioned in some records to ‘have darkened the sky’ when migrating!), wolves, bears, cougars, deer, and buffalo roaming these regions!

European colonizers quickly realized that these grasslands were great land for cattle and hunting, and thus started settling and claiming the native tribes’ lands. However, the new inhabitants did not continue the practice of burning, which led to the habitat starting to degrade and finally becoming less appropriate for cattle and cropping.

Eventually, these lands were relegated as ‘useless’ lands and were thus prime land for building or just reinvaded by pines and other trees, which were used for timber. I sometimes try to imagine what these lands — today just 30 minutes away from my house — may have looked like with those large fascinating animals living right here.

Dusted Skipper
Fig. 4 – The Serpentine Barrens are the habitat for several rare moth and butterfly species, such as the Dusted Skipper (Photo: A. Wells).

Today, the Serpentine Barrens are protected and managed with fire in several parts of the state. A large part of these protected lands are not open to the public. However, we are lucky that some places are indeed accessible to the public and can be visited throughout the year.

The largest remnant of Serpentine Grasslands on the Eastern Coast of the US is west of Baltimore, in the Soldiers Delight Natural Environment Area. Another public land where some remains of Serpentine Grasslands are still visible is in Northern Baltimore, at Lake Roland Park.

I am lucky enough that I can visit and work in these fascinating places. If you have never been to them and would like to see these local jewels, take me up on the invitation and consider hiking some of their trails. The spring and summer are gorgeous on these lands, and who knows, you may be lucky enough to see one of those rare beauties that still live there!

By Anahí Espíndola, Assistant Professor, Department of Entomology, University of Maryland, College Park