Sunday, September 25, 2011

Plant Communities

A native plant by itself is not a native plant; it is “a plant”.  Native plants live in natural communities that are defined by their location aspects such as elevation, landforms, moisture level, geological characteristics, soils and are even influenced by the hand of humans over the last centuries.  While we can and do enjoy them in our gardens, understanding and appreciating their role in a community is often the basis for becoming a better advocate for habitat conservation.

Magnolia grandiflora

Southern Magnolia (Magnolia grandiflora) is an example of a plant that is native to the southeastern United States but which is used in landscapes in whatever areas are warm enough to support it.  I was recently vacationing in the San Francisco area and found it used quite often there.

I recently read Timothy Spira’s book “Wildflowers and Plant Communities of the Southern Appalachian Mountains and Piedmont” and learned a lot about 21 different plant communities in this particular region (which includes Atlanta). I highly recommend the book and hope to present here some of the things that I learned from it. This is a recent book, published in early 2011.

The region covered in the book extends from northern Virginia, a sliver of West Virginia, a slightly larger sliver of Tennessee, most of North Carolina, South Carolina, the northern half of Georgia and a small area of east/central Alabama. The area known as the Coastal Plain (the eastern portions of Virginia, NC, SC and the southern half of Georgia in this case) is not included and has its own very unique and diverse plant communities.  This book covers the 21 major plant communities found in the southern Applachian mountain and piedmont regions of the southeastern United States.

Twenty-one sounds like a lot of unique communities, doesn’t it?  It can be a little simpler if I list the high level categories:

In the mountains there are 4 categories: High-elevation communities (6 of those), Low-elevation moist to wet communities (5), Low-elevation dry communities (2).  In the piedmont (the author reminds us that “piedmont” literally means “foot of the mountains” – I love that!) there 3 categories: Moist to wet communities (3), Dry communities (3), and Roadside and Field.

The book includes some beautiful pictures and in-depth plant profiles so that it also serves as a field guide.  Before one gets into descriptions of plants, however, the author lays the groundwork for understanding how these communities have come to be.  He provides good background on factors as far back as when and how the mountains formed as well as the role that climate played in altering habitats and allowing species to expand or contract their range.  More recent factors include the effects of human activities and invasive species.

This area of the United States is incredibly diverse – according to the author: “the southern Appalachians support more tree species than any other area of comparable size in North America”.  In general the area is considered to be a temperate deciduous forest – or would have been without human intervention.  There are some particular areas that are not a forest, and these areas serve to increase the diversity of the plants even more.

The picture here was taken on the Shirley Miller Wildflower Trail in the area known as The Pocket at Pigeon Mountain (Walker County, Georgia).  The trail winds through a rich cove forest community.

Ferns, Trillium and dwarf Iris cristata on the Shirley Miller Wildflower Trail

The details provided in the description of the region covered by the book are fascinating.  For example, the region has 3 national parks and 6 national forests; together these areas have the greatest concentration of public land in the eastern United States.  As you read more about the wonderful habitat these areas protect, one is grateful that these areas have been conserved.  However, as you may know, imported diseases have devastated many of the trees in the area: American chestnut (chestnut blight), Fraser fir (balsam woolly adelgid), and Canada and Carolina hemlocks (hemlock woolly adelgid) are once dominant tree species that have been or are in the process of being destroyed.  The plant communities with hemlocks (Tsuga spp.) are changing right before our eyes as the woolly adelgid spreads.  Our increased understanding of these communities affords us a chance to provide some measure of protection here and in yet unaffected areas as we recognize more the importance of conservation.

Ok, that pretty much covers Part 1 of the book.  The remaining parts are:

Part 2: a pictorial representation of each of the 21 communities.  These collections give you a preview of the plants you might find.  A sample group of plants is shown to represent each of the 21 communities:

Spruce-Fir Forest (Mountains)
Grassy Bald (Mountains)
Heath Bald (Mountains)
High-Elevation Rock Outcrop (Mountains)
High-Elevation Red Oak Forest (Mountains)
Northern Hardwood Forest (Mountains)
Rich Cove Forest (Mountains)
Acidic Cove Forest (Mountains)
Spray Cliff (Mountains)
Rocky Streamside (Mountains)
Mountain Bog (Mountains)
Chestnut Oak Forest (Mountains)
Pine-Oak-Heath (Mountains)
Forest Edge (Mountains)
River Bluff Forest (Piedmont)
Alluvial Forest (Piedmont)
Basic Mesic Forest (Piedmont)
Oak-Hickory Forest (Piedmont)
Xeric Hardpan Forest (Piedmont)
Granite Outcrop (Piedmont)
Roadside and Field (Piedmont)

The picture below is a "roadside and field" community near my house.  Roadsides can be tricky - sometimes they are full of invasive or naturalized plants - not natives much at all.  But this one is good: it has at least 3 different species of Eupatorium, at least 3 species of Goldenrod (Solidago), at least 3 species of grasses (and perhaps a couple of non-native ones), several different asters, blue curls (Trichostema dichotomum), and slender leaf false foxglove (Agalinis tenuifolia) - just discovered this morning! 

Part 3 provides detailed descriptions of each of the communities. These profiles include Distinguishing features, Vegetation overviews, Seasonal aspects, Distribution, Dynamics, Conservation aspects, Suggested reading references, and good lists of Trees, Shrubs, Herbaceous plants, and Rare plants.

Part 4 has detailed species profiles for the plants listed in Part 3. One feature that I particularly like is the “Ecology” section of the profile. This section provides some details not found in the usual plant guides.

The book finishes up with a Glossary, a list of recommended natural areas throughout the region (with descriptions of the exceptional features to be found in each), suggested books for further reading (which includes some of my favorites), an index of scientific names and a second index of common names.
The depth of information in this book is excellent, and it is presented at a level that can be used by all levels of naturalists.  Back to that Southern Magnolia - it's not listed in the book, by the way.  That plant is not indigenous (i.e., naturally found) in the Southern Appalachian Mountain or Piedmont communities.  You can expect to find it naturally in south Georgia - in the Coastal Plains communities.


  1. This sounds like a wonderful resource for the App. and Piedmont. I'll bet it would be a great template for all the other plant communities and regions. Our State DNR has a 3 volume series of plant communities but is not user friendly for the interested gardener or naturalist.

  2. This looks terrific! It's getting kind of funny watching plant books overtake computer books on the bookcase by my desk :)

  3. UUggh! I hope Mr. Spira sent you a thank-you note for buying (and then reading!) his book. All that knowledge makes my head hurt! On a more serious note, why is it that roadside areas are filled with invasives and naturalized plants?

  4. Jeff, I think that roadside areas are prey to the invasion of invasives and naturalized plants because those areas are "untended" or "unmanaged". In managed areas weeds are kept in check by gardeners and by mowers, both of which keep many plants from going to seed. On roadsides, those plants often get the chance to grow, bloom and set seed with abandon, thus increasing the populations. My thoughts on that.

  5. Makes complete sense. I guess I was thinking about how a forest "replants" itself following a storm or disturbance. Apples & oranges though. The forest has wonderful soil, the seeds that fall and sprout are 'of the forest', and the larger trees "manage" the regrowth.

  6. Jeff, my impression is that we have the highway crews to thank for the high proportion of invasive plants on roadsides. Their mowing equipment is quite efficient at moving seeds and rhizomatic bits from one infested spot to another.