A Sense of Place
No matter the time of year, it doesn’t take long for visitors to appreciate what a special place Bowman’s Hill Wildflower Preserve is. Repeated visits to different portions of the Preserve will be rewarded with new discoveries of different plants in bloom and new encounters with the multitude of birds, insects, mammals and aquatic life that depend upon these plants. Where else is it possible to see Baltimore checker spot butterflies flitting near white turtlehead plants, pileated woodpeckers hammering away on a sugar maple tree in search of insects, and bright orange chanterelle mushrooms sprouting up on the forest floor after a warm summer rain?
Over 700 of Pennsylvania’s 2,000 native plant species grow naturally on the Preserve’s 134 acres. For this richness of native plants, credit the Preserve’s diverse habitats—mature hardwood forests, a meadow, steep hillsides, a creek, a pond and other wetlands—and three distinct geological zones that influence their overlying soils. Credit also the fact that, since its founding in 1934, the Preserve’s dramatic landscape has been actively managed to promote native plant diversity.
As the nation's one-and-only living museum specifically devoted to native plants, the Preserve has something to offer everyone and we invite you to explore this special place. Wander almost 4-1/2 miles of trails as you reconnect with the natural world. The Preserve is here for you to explore and enjoy—no matter where you come from there is a place here for you to grow. Visit and you will soon discover why the Preserve is the place where mind, heart and spirit bloom!
The Preserve’s underlying geology is at the root of its native plant story. During the Triassic Period approximately 220 million years ago, the place we call the Preserve was part of a rift valley that formed as the supercontinent Pangea pulled apart. That great spreading rift valley became filled with the muddy reddish-brown sediments eroded from the mountains on either side. The sediment, packed hundreds, even thousands of feet deep in places, eventually hardened into a red-colored shale field called the Passaic Formation.
During the Jurassic Period, approximately 150 million years ago, magma from the earth’s mantle pushed its way up into the Passaic Formation shale. The soft shale fractured along huge fault lines and was pushed upwards as the magma intruded into the giant cracks that opened up in the shale. The magma came within several hundred feet of the surface, but never made it that far. If it had broken through, it would have become an above-ground lava flow. Instead, over many thousands of years, the magma slowly cooled and, under pressure from the shale above that encased it, it formed a dense crystalline igneous rock called diabase.
In the 150 million years since that violent and defining geological event, the soft, uplifted shale has been worn away by wind, water and living organisms, such as rock-dissolving lichens and tree roots that infiltrated and fractured the rock. These factors exposed the tops of these diabase intrusions that once had been hundreds of feet underneath the shale. One of the exposed tops of the diabase intrusions is Bowman’s Hill itself. Others include nearby Jericho, Solebury and Buckingham mountains. They are all part of a larger shale/diabase formation that extends from the Sourlands of central New Jersey westward toward Lancaster and southerly towards York, Pennsylvania, and into Maryland.
In addition, wherever the red shale came in close contact to the intruding magma, the shale was ‘baked’ by the heat and transformed into a harder and denser metamorphic rock called hornfels. These tree rock formations present at the site—red shale, diabase and hornfels—largely determine the soil types and characteristics that lie above them. Specifically, the underlying geology has a direct effect upon the soil depth, permeability, chemistry, nutrients, pH and trace mineral constituents. Additionally, the geologic history of the Preserve created the slope, steepness and orientation (north facing slopes are wetter and cooler) of the landforms we see today.
Much of the Preserve’s soil on the northern two-thirds of the property is derived from the weathering of the underlying sedimentary Passaic formation shale. The pH ranges from 4.5 to 6.2 and supports a wide diversity of plant life. Most notable in this section of the Preserve is the Marshmarigold Trail, which winds along a seep that, fed by subsurface water, flows during the springtime. Plants that flourish in this wetland include sensitive fern (Onoclea sensibilis), royal fern (Osmunda regalis), false hellebore (Veratrum viride) and marsh marigold (Caltha palustris)—the trail’s namesake.
The ridge known as Bowman’s Hill features a soil derived from the underlying diabase geology that has a pH range from 3.9 to 6.0. With its acid soil and ample moisture, the lower slopes of the hill support the growth of hemlocks (Tsuga canadensis), striped maples (Acer pennsylvanicum) and great rhododendron (Rhododendron maximum). In contrast, the upper slopes of the hill drain quickly and are home to more drought-tolerant species known collectively as a dry oak-hickory forest.
The hornfels formation between the diabase ridge and the Passaic formation shale forms much of the soil within the Pidcock Creek valley as it winds its way through the Preserve. It is in this swale that the greatest diversity of spring ephemeral wildflowers is found, specifically along the Mary K. Parry Trail. Occasional flooding, along the with the ongoing weathering of the surrounding bedrock, has created a “goldilocks” effect where the soil chemistry and hydrology is “just right” to support a species-rich community of native wildflowers each spring. These include Virginia bluebells (Mertensia virginiana), trillium (Trillium sp.), twinleaf (Jeffersonia diphylla), Jacob’s ladder (Polemonium reptans) and wood poppy (Stylophorum diphyllum).
As a result, within a relatively compact area, the Preserve is endowed with a rich diversity of landforms, soil types and drainage patterns. This geologic diversity translates directly into a diversity of habitats that allows the Preserve’s rich collection of native plants and plant communities to thrive.
While the underlying geology at the Preserve is certainly the most significant factor in determining the type and diversity of plant communities growing at the Preserve, the use of the land by humans over the centuries has also had an impact on the present-day plant communities. Historical accounts tell of a Lenni-Lenape village at the base of the hill near the Delaware River. The natives called it “Win-Na-Haw-Caw-Chunk,” translated as “hill near the water,” and it was a visible landmark where local tribes gathered and traded.
Europeans arrived in the mid-17th century. The first among them were the Dutch, whose work can be seen in the remains of an abandoned and now filled-in copper mine near the Parry Trail.
The English colonists who followed soon thereafter twice clear-cut the land that is now the Preserve—first during the late 17th/early 18th century in order to make way for agriculture and to provide building materials for the growing colonial city of Philadelphia. The land from the river westward to Pidcock Creek was tilled and used in agricultural production, mostly as wheat fields, the grains of which were processed by the adjacent mill. The land located on the floodplain on the west side of the creek (Audubon Birding Trail, Violet Path, Gentian, Fern and Medicinal trails) was too wet to support crops reliably and, instead, was used as pasture for grazing livestock.
It is important to remember that there is no true “virgin” forest at the Preserve—it is all second-growth forest that has regenerated after being cut down. Some of the original understory inhabitants of that forest—trout lily, bloodroot, spicebush and Christmas fern—persisted despite numerous repeated disturbances. Most of the trees living on the property today are descendants of the trees that originally inhabited the Preserve. However, even the oldest trees at the Preserve are no more than 140 years old.