Last weekend, I traveled down to Baltimore to see some friends and, while I was there, decided visit Soldier's Delight Natural Environment Area, one of my favorite places to go hiking when I was living in the area for school. It's also one of my favorite places in general, both because exploring it was an excellent use of time during the pandemic and because it is home to some really cool geology which in turn underlies a rare and fascinating ecosystem.
Hundreds of millions of years ago, the land that now makes up Soldier's Delight was at the bottom of an ancient sea, where large deposits of a magnesium-rich, greenish rock called serpentinite formed. Over time, the serpentinite was eroded by wind, water, and ice until it became a thin, rocky soil too poor in nutrients for the more common Midatlantic plant communities to survive in. Instead, Soldier's Delight is dominated by a unique and rare community of plants known as a Midatlantic serpentine barren. This community consists mainly of stunted oaks, junipers, and pines, as well as a number of grasses and wildflowers, including many endemic species specifically adapted to live in the magnesium rich, nutrient poor soils found out on the barrens. The result is a beautiful, open landscape that isn't quite like anything else that I have seen in this part of the country.
When I visit Soldier's Delight, I usually walk the Choate Mine trail, a roughly two-mile loop that starts on the east side of Deer Park Road in Owings Mill, Maryland. The other option, the Serpentine Trail, takes hikers through some of the parks most intact serpentine barrens, but tends to be a bit more crowded and doesn't offer a comparative variety of different habitats to those found on the Choate Mine trail. Since I'm usually bird watching during my visits, that variety is a pretty big draw.
The first habitat type that one passes through on the Choate Mine trail (assuming you use the northern entrance) is a scrub thicket. This is as good a location as any to introduce yourself to the two main kinds of tree found in the park. The first of these is the Virginia pine (Pinus virginiana). Like most pines, the Virginia pine prefers to grow in open sun and, as a result, they are often among the first tree species to colonize recently open spaces (Little et al. 1980). This, combined with their ability to live in poor, sandy soils means that, if they are allowed to, Virginia pines would take over the barrens, forming thickets like this one and shading out all the rare flowers and grasses that grow in the more open areas. Virgina pines used to be excluded from the barrens by a mixture of natural and human-managed fires, as the tree's thin bark leaves it very susceptible to flames. Since European colonization, however, natural fire regimes have been suppressed, resulting in large areas turning to thickets dominated by Virginia pine and greenbrier (Tyndall 2022a). Today, extensive restoration projects, including controlled burns, are underway to try and create a balance between the thickets and the barrens.
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Blackjack oak (Quercus marilandica)
The second kind of tree that is commonly found at Soldier's Delight is the oak (Quercus sp.), with the most common species, at least in my experience, being the blackjack oak (Quercus marilandica). Like the Virginia pine, blackjack oaks require direct sunlight and can grow even in poor, sandy soils like those found on the serpentine barrens. Unlike the pines, however, mature blackjack oaks are very resistant to fire and, in fact, depend on it to some extent to create openings where young trees can get enough sunlight to grow (Abrams 1992; Dey and Fan 2009). Historically, small fire-resistant oaks such as the blackjack, the post oak (Quercua stellata), and the bear oak (Quercus ilicifolia) would have been some of the only trees living out on the barrens due to their ability to persist and even thrive despite frequent fires (Tyndall 2022c). Today, this remains the case in restored sections of the park; in other areas, you may find them among the thickets, but they can also be shaded out if the canopy coverage becomes too much.
Both oaks and pines provide important sources of food and shelter for a number of animals, including deer, wild turkeys, squirrels, and Lepidopterans (moths and butterflies). The most obvious of these, however, are the songbirds, of which there are always a great many singing from their hidden perches in the thicket. Year round, one can see and hear Carolina chickadees (
Poecile carolinensis) and tufted titmice (
Baeolophus bicolor) foraging in the treetops, while early spring brings the
bubbling song of the pine warbler (
Setophaga pinus) and the sarcastic
yank-yank of the red-breasted nuthatch (
Sitta Canadensis), both lovers of forests with plenty of conifers. On this particular morning, I also heard, but unfortunately did not see, a
white-eyed vireo (
Vireo griseus), an obligate scrub dweller with striking white irises. And, of course, there were plenty of the thicket's most entertaining summer visitors, the eastern towhees (
Pipilo erythrophthalmus), singing their yearly request to
"drink-your-tea!" I shout back my own traditional response - "Don't tell me what to do!"
The Barren:
I believe that these are sandplain gerardia (Agalinis acuta), but in general, one should take my wildflower IDs with a grain of salt. Please do correct me if I'm wrong
After spending a little time looking at the trees and listening to the birds in the thicket, I continued on down the path and eventually emerged out into the open space of the barren proper, where many of the parks 39 rare or threatened plant species grow. Some of these, such as the sandplain gerardia (Agalinis acuta), can also be found in the sandy soils of certain endangered coastal habitats, while others like the serpentine aster (Symphyotricum depauperatum) and the serpentine chickweed (Cerastium arvense var. villosissium) are found almost exclusively in the Midatlantic serpentine barrens.
Lyre-leaf rock cress (Arabidopsis lyrata)
Unfortunately, I wasn't able to find any rare plants this time around, though given my general lack of knowledge when it comes to wildflowers, that really isn't much of a surprise. What I was able to find looking along the edges of the trail were members of a few of the more common spring blooming taxa, including lots of azure bluets (Houstonia caerulea), some cinquefoils (Potentilla sp.), and a few violets (Viola sp.). I also found a number of lyre-leaf rock cress (Arabidopsis lyrata) growing on the sides of an old chromite mining pit near the trail. Such pits can be found throughout Soldier's Delight and up until around 1860, they produced a significant amount of the world's chrome supply. Today, the areas around the abandoned entrances are home to tough plants such as rock cress and ebony spleenwort (Aspleniurp platyneuron), as well as reptiles and amphibians such as eastern rat snakes (Pantherophis alleghaniensis) and long-tailed salamanders (Eurycea longicauda), which like to hide in the rocky crevices. The presence of chromite in the soils of Soldier's Delight and other serpentine barrens does not appear to have a major impact on plants, as it is not in a form that is biologically available to them (Tyndall 2022b). Other heavy metals, such as nickel, are only biologically available at low levels, but there is nonetheless some interesting evidence that local populations of lyre-leaf rock cress are especially well adapted to growing in high-nickel soils, at least compared to other plants from non-serpentine populations (Veatch-Blohm et al. 2017).
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Prairie warbler (Setophaga discolor)
Besides wildflowers, the edge between the thicket and barren habitats is an excellent place to look for the several species of scrub and grassland birds that breed at Soldier's Delight. Of these, my personal favorite is the prairie warbler (Setophaga discolor), a beautiful songbird with a black-streaked, bright yellow belly, a brown-grey back, and a warm, buzzy song. Like many scrub-dwelling birds, prairie warbler numbers shot up in the early twentieth century as the mass abandonment of agricultural land on the east coast created vast areas of overgrown fields and, after some time, the sorts of dense thickets that they prefer to nest in (Nolan 1978). Eventually, however, these thickets were shaded out and replaced by the hardwood forests that we see covering much of the region today, causing scrub-dwelling species to decline significantly from their mid-century peak. Today, prairie warblers can still be found throughout the eastern U.S., but their habitats are a lot more limited. At Soldier's Delight, they are joined by other birds of open spaces and scrublands, including field sparrows (Spizella pusilla), white-eyed vireos (Vireo griseus), and yellow-breasted chats (Icteria virens).
The Creek:
American goldfinch (Spinus tristis)
After trekking across the barrens for a while, I eventually came to the banks of Red Run, one of a few creeks that run through Soldier's Delight. During the summer, Red Run is a great place to observe the aerial acrobatics of eastern wood-peewees (
Contopus virens) as they hunt for flying insects above the water, but it seems I've arrived a little too early to see them. Instead, I am greeted by a large, noisy flock of American goldfinches (
Spinus tristis) feeding on oak flowers up in the canopy. Below them, a few white-throated sparrows (
Zonotrichia albicollis) sing in
operatic falsetto from a patch of greenbrier and across the creek, a red-breasted woodpecker (
Melanerpes carolinus) hammers into the bark of a dead snag.
American sycamore (Platanus occidentalis)
As you might imagine, the plant communities around the creeks of Soldier's Delight are a little richer than the community growing out on the dry, rocky barrens. In the area around this part of Red Run, the soil type seems to change into something a little closer to what the Midlantic's more common plant species can handle and as such is home to a fairly typical stream-side community, including plenty of skunk cabbage (Symplocarpus foetidus), sensitive fern (Onoclea sensibilis), and red maple (Acer rubrum). On this trip, I also noticed for the first time that there are several large American sycamores (Platanus occidentalis) with much wider canopies than most of the other trees growing along the creek, a feature that is usually indicative of trees that grew up in open spaces. Sycamores, like red maples, prefer to grow in wetland habitats, especially along the banks of streams and rivers. Likely due to the unpredictable nature of these habitats, they have evolved to grow very quickly and reproduce young; they are also often some of the first trees to colonize a floodplain after it has been disturbed (Little et al. 1980). Given these facts, it seems likely the difference in size between the sycamores and the other trees in the area can be explained by a situation in which the field just beyond the tree line once extended further towards the bank. At a certain point in the past, the owner of the field stopped managing this section and the sycamores were the first trees to colonize, allowing them to quickly grow up and out to take full advantage of the ample sunlight. Then, over time, more shade tolerant species like the red maples would have started to grow under the sycamores, eventually creating the young forest we see today.
The Forest
Hardwood forest at Soldier's Delight
The final habitat type that I passed through on the Choate Mine trail was a typical, Midatlantic hardwood forest, located just uphill from Red Run. I'm not exactly sure why the barrens switch to forest at this spot, but as I mentioned in the previous section, I would guess that it probably has to do with a change in soil composition. Whatever the reason for the forest's existence, it provides an interesting opportunity to compare serpentine plant communities with those which can be found throughout most of the rest of the Midatlantic region. For example, while a significant portion of the trees growing on the barrens and in their associated thickets are coniferous, most of the trees in this forest are deciduous hardwoods, such as red maple (Acer rubrum), tulip poplar (Liriodendron tulipifera) and various kinds of hickories (Carya sp.). Conifers tend to do better in dry, nutrient poor soils such as those found on the barrens because their thin, waxy needles prevent excessive water loss, while their evergreen status ensures they don't have to use extra nutrients to grow new leaves each year. Conversely, deciduous hardwoods will often outcompete conifers in wetter, more nutrient rich soils, at least in the Midatlantic. The one group of hardwoods that is common in both the forest and barren communities is the oaks, though here in the forest, we mostly see larger species such as the white oak (Quercus alba), the black oak (Quercus velutina), and the chestnut oak (Quercus montana). Interestingly, the understory of this particular forest also has a lot of black gum (Nyssa sylvatica), in addition to the more common mountain laurel (Kalmia latifolia) and flowering dogwood (Cornus florida). This is interesting because I always thought these trees only grew in swamps, but apparently, they will grow in uplands as well - who knew? (I guess Little et al. did, but who else? Probably nobody).
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White-tailed deer (Odocoileus virginianus)
With all the interesting trees (chestnut oak, red maple, black gum, and tulip poplar are some of my favorite species), I admit that I wasn't paying a ton of attention to the animals in this part of the park. I did hear a pileated woodpecker (Dryocopus pileatus) and saw a lovely eastern tiger swallowtail butterfly (Papilio glaucus) flying down the path, but I very nearly missed a small heard of white-tailed deer (Odocoileus virginianus) moving up the hill just in front of me. Historically, it was during white-tailed deer hunts that the Native Americans living around Soldier's Delight would have lit many of the human-managed fires that helped to keep the barrens from being overrun by thickets. After European colonization, deer populations were severely depleted in the eastern U.S., but this trend was reversed in the early twentieth century through extensive restoration efforts. Today, as in much of the region, a lack of large predators combined with lots of good habitat created by human activities has allowed deer populations around Soldier's Delight to increase to levels that present a real threat to rare or endangered plant species due to over browsing (Tyndall 2021). As such, the park has been opened up to regulated hunting, supplemented by more organized cull operations in order to control deer populations.
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And that's the end of the tour! I've only described about half of the Choate Mine trail, but after you pass through the hardwood forest, you just head back down into more barrens and thickets like the ones I've already described. Altogether during this trip, I saw or heard a total of 29 different species of birds, as well as plenty of insects and plants. No herps, unfortunately, but that's just a good excuse to come back again soon!
Of course, that's easier said than done given that I live six hours away by car, but that's alright. For me, Soldier's Delight is like an old friend, the kind which I can go without seeing for months at a time, only to pick up again with the same comfort and interest almost immediately after returning to its boarders. It's the kind of the place that is so unique that even the most familiar seasonal events take on a fresh sense of meaning when viewed through the lenses of an ecosystem that this so unfamiliar to a New Englander like me. If you live in the area and have never been, I would absolutely recommend that you check it out. Just make sure you stay on the trail and watch your step - there are species found nowhere else on the planet growing just at the edge of the path.
Sources:
Abrams, M.D. (1992). Fire and the development of oak forests. Bioscience, 42 (5) 346-353.
Dey, D.C., and Fan, Z. (2009). A review of fire and oak regeneration and overstory recruitment. In Proceedings of the 3rd Fire in Eastern Oak Forests Conference. GTR-NRS-P-46.
Little, E.L., Bullaty, S., Lomeo, A., Rayfield, S. and Buehl, O. (1980). National Audubon Society field guide to trees, eastern region. Alfred A. Knopf.
Nolan Jr., V. (1978). The ecology and behavior of the prairie warbler, Dendroica discolor. Ornithological monographs; no. 26, p8-11.
Tyndall, R.W. (2021). Changes in herbaceous species variable after enhanced hunting effort for white-tailed deer in Soldier's Delight serpentine ecosystem in Maryland. Castanea, 85(2), 327-342.
Tyndall, R.W. (2022a). Landscape history of the serpentine barrens. Friends of Soldier's Delight. Link
Tyndall, R.W. (2022b). Plant growth on serpentine soil. Friends of Soldier's Delight. Link
Tyndall, R.W. (2022c). Serpentine vegetation: past and present. Friends of Soldier's Delight. Link
Veatch-Blohm, M.E., Roche, B.M, and Dahl, E.E. (2017). Serpentine populations of Arabidopsis lyrata shows evidence for local adaptation in response to nickel exposure at germination and during juvenile growth. Environmental and Experimental Botany, 138: 1-9.
Wennerstrom, J. (1995). Soldier's delight journal: exploring a globally rare ecosystem. University of Pittsburg Press.
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