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A Year in the Life of Pimmit Run: The Natural Plant Communities - Revisited

Updated: Apr 26, 2022

(The original version of this blog, posted in late winter 2021, has been updated with some historical background due to increased interest and relevance!)

Plants are like people – they like to hang out with others that thrive in a particular common environment. This tendency of native plants to align ecologically and form communities that reflect the conditions in which they are best suited, i.e. natural plant communities, helps us anticipate what plants we might encounter as the forest wakes up.

Bloodroot (Sanguinaria canadensis)) and Black Cohosh (Actaea racemose), close buddies of the Basic Mesic Hardwood Forest

The Pimmit Run Stream Valley Park corridor is remarkable because, while it is surrounded by dense development, parts of it remain relatively undisturbed. In many areas of the park, indigenous native plant communities continue to thrive as long where they are not crowded out by aggressive, non-native invasive plants. Wandering along a not-too-large portion of the stream valley, one can experience numerous natural plant communities and begin to develop a deeper understanding about them and their relevance to broader habitat restoration and regeneration strategies.

Waugh Wrote About Natural Plant Communities in 1917

A Little History

The idea of natural plant communities is not a new topic. In fact, my favorite definition of the concept is from a book written by Frank Waugh and published in 1917, if you can believe it: "The Natural Style in Landscape Gardening.” In it, Waugh wrote: “Practically every [plant species] is associated habitually with certain other species. Thus they form set clubs or societies. And these friendly associations, based upon similarity of tastes and complementary habits of growth, should not be broken up. If we as landscape gardeners desire to preserve the whole aspect of nature, with all its forms intact, we will keep all plants in their proper social groupings.” As noted by Waugh, the natural plant community defines the spirit of the place. In this book, he encouraged landscape architects to “first and foremost, endeavor to understand the spirit of...[the] landscapes.”

Roberts and Rehmann wrote about Natural Plant Communities in 1929

Then, in 1929, Edith Adelaide Roberts and Elsa Rehmann published "American Plants for American Gardens." The subtitle of the book is "Plant Ecology -- The Study of Plants in Relation to Their Environment," which happens to be a really nice concise definition of the term "natural plant community." In the book, Roberts and Rehmann document eleven common natural plant communities found in America at that time. These archetypical communities have an enduring quality and broad relevance to a wide range of ecological initiatives today. In his Foreword to the republicized 1996 edition of this book, Darrell Morrison wrote: "the volume has a message that is as valid today as it was the day it was published: the naturally evolved associations of native plants within a particular region can provide both information and inspiration for the design of landscapes and gardens that are ecologically sound and aesthetically satisfying" (page xi).

For many decades following the publications of these volumes, the ideas the authors wrote about concerning natural plant communities and the connection of plant ecology to the environment fell out of vogue. Why that is the case is a story for another day. Suffice it to say that current appreciation for these topics is strong, and may reflect the fact that we live in an increasingly complex world and are having to cope with the impacts of climate change. Native landscapes that are well suited to their environment are most likely to be resilient. Understanding the natural plant communities associated with a given site is key to successful native garden design and habitat restoration.

The Natural Plant Communities of Pimmit Run Stream Valley Park

The rich forests, floodplains, and upland woodlands along the Pimmit Run Stream Valley Park host at least three dominant native plant communities (pictured below left to right): 1) Basic Mesic Hardwood Forest, 2) Small Stream Floodplain Forest, and 3) Oak-Beech/Heath Forest. Each community has its own personality and native plant incumbents, although there is some overlap. Let’s pay each a short visit. And these natural plant communities are so common in our region that they are relevant for many sites undergoing habitat restoration or regeneration.

1. First Up: The Basic Mesic Hardwood Forest in Your Backyard

These are the luxuriant forests behind the homes and usually along protected slopes that lead down to the streambeds, characterized by dense tree canopies, lush understories, and ground level herb layers. They can be a delight to explore, particularly in the spring when ephemerals and fiddleheads appear in abundance. Natives thrive in these forests as long as the invasive species are held in abeyance. This plant community is highly relevant to residential landscapes that feature a tall canopy, significant shaded areas, and woodland gardens. Some of my favorite plants from this community are shown and listed below by row:

1. American Beech, Tulip Poplar, White Oak, Red Oak

2. Pawpaw, Spicebush, Enchanter's Nightshade, False Solomon's Seal

3. Black Cohosh, Christmas Fern, Trout Lily, Cutleaf Toothwort

4. Toadshade, Bloodroot, Mayapple, White Wood Aster

2. Getting Your Feet Wet: The Small Stream Floodplain Forest

Moving down closer to the stream we encounter the floodplains of Middle Pimmit Run, an area subject to frequent overflow where the plants need to be flood tolerant and the soil is silty and sandy. While a closed forest with overstory canopy, understory, and herb layer, the latter may be a bit weedy due to occasional flooding. This plant community is relevant to wet residential landscapes or those with stormwater drainage challenges. The plants associated with the floodplain forest can tolerate wet conditions, shade or sun, and occasional flooding. These plants are usually happy in a rain garden or swale situation in a residential setting. Here are some favorites from this community, shown and listed by row below:

1. American Sycamore, Tulip Poplar, Red Maple, Slippery Elm

2. Spicebush, American Hornbeam, Pawpaw, Jack in the Pulpit

3. Carex/sedge, Enchanter's Nightshade, Spring Beauty, Virginia Knotweed

4. Calico Aster, Common Blue Violet, White Avens, Trout Lily

3. Hiking the Upland Ridge: The Oak-Beech/Heath Forest

A different experience can be enjoyed by those who hike up the north-facing upland forest trails. This plant community typically occurs on north-facing upland woodland slopes with acid soil conditions and features a dense tree canopy layer, a loose evergreen understory and thick layer of leaf material and rock with some groundlayer plants. This plant community is relevant to residential landscapes that are drier with more acidic soil. Some of the more finicky native shrubs like Mountain Laurel and Pinxterbloom Azalea are in this community. Some truly special natives can be found here, including those shown and listed by row below:

1. American Beech, Chestnut Oak, American Sweetgum, Red Oak

2. Red Maple, Sassafras, Black Gum, Serviceberry

3. Flowering Dogwood, Mountain Laurel, Pinxter Flower Azalea, Mapleleaf Viburnum

4. Spotted Wintergreen, Indian Cucumber, Poverty Oat Grass, and Christmas Fern

So there we have it -- the native plant communities of this portion of Pimmit Run Stream Valley Park. This is not to say that one doesn't come across additional plant communities and surprises along the way. That is part of the mystery of nature. But now, at least, we are prepared to watch what emerges and blooms as spring approaches. We may observe something new. But usually, if we investigate, it is a friend of the community that belongs there.

p.s. all photos on this blog were taken by the author along the Pimmit Run Stream Valley.


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