Communities, Guilds and Modules: Grouping Plants

When explaining the need for native plants in the landscape we often talk about the need for a constant supply of food, namely blooming flowers, for pollinators, and how planting groups of plants with successive bloom times throughout the year will ensure that your pollinators always have plenty to eat.  It requires a bit of forethought and research (or just ask us), but the rewards are flowers and bees/butterflies/birds in your yard all year.  That sort of long term planning is also useful when thinking about your the physical setting where you want to put your plants (i.e. your yard).
Beech trees thrive in moist bottom lands. Have you ever seen one on a hilltop?

Beech trees thrive in moist bottom lands. They would not last long on a dry hilltop.

 Botanists refer to naturally occurring groups of different plant species as ‘communities;’ and there are LOTS of them.  The Natural Communities of Georgia is a massive 700 page book that exquisitely details the plant species that occur in each little environmental  variation of a given area in Georgia.  It just came out last year, and at $60 it’s a steal.  If you REALLY want to get to know the flora of the land you inhabit, this is THE reference you need.  Digression aside, there are many, many combinations of plants that naturally occur together.  The particular mix of geology, slope, aspect, moisture, light, wildfire, animals, and many other variables that make up a landscape determine what plants are able to survive and thrive there.
Trillium and Bloodroot also thrive in moist bottom lands. They bloom early in the year before the Beeches unfurl their leaves.

Trillium and Bloodroot also thrive in moist bottom lands. They bloom early in the year before the Beeches unfurl their leaves and cast a deep shade.

 When we introduce the human decision making process to the equation with the question “What shall I plant?” we can all take a lesson from nature.  By studying communities one can learn much about how every niche can be filled with a plant. Permaculturists such as Bill Mollison and Toby Hemenway have popularized the concepts of ‘guilds’ and ‘plant stacking’ to describe attempts to emulate natural communities and succession processes with human plantings.  The guild is basically a radial planting pattern with a central focal point, most often a tree or large woody shrub.
Midwest Permaculture has an awesome e-booklet (.pdf) available for free that explains this concept way better than I can with fancy graphics and examples of guilds for many different species of tree.  The Oak guild (pg. 13) should be of interest to most people in the Piedmont.
Plant stacking refers to the use of vertical space through time.  In a mature guild you would have your (top to bottom) canopy trees, midstory or sub-canopy trees, understory trees, woody shrubs, and the herbaceous ground layer.  This space also moves through cyclical time each day and year, with the daily and seasonal weather variations offering dynamic microclimates for a diverse collection of plants.  But we don’t all have mature trees just ready and waiting for those spring bulbs underneath.  If you start with a four foot tall oak sapling (or an acorn!) you can maximize the space by planting a fast growing, short-lived tree or shrub that will also help shield the young oak from wind and harsh temperature changes.
 Pictured above are a few of the layers in a mature Oak-Hickory-Pine canopy in an Atlanta park.  Ground layer, top left, is covered with Virginia Creeper (Parthenocissus quinquefolia), Muscadine (Vitis rotundifolia) and Greenbrier (Smilax sp.) among others; Shrub layer, top right, has an Oak-Leaf Hydrangea (Hydrangea quercifolia); Understory has a Flowering Dogwood (Cornus floridus) beneath an Oak; the midstory and canopy are occupied by a mix of Hickory (Carya sp.), Oak (Quercus sp.), Tulip Poplar (Liriodendron tulipifera), Pine (Pinus sp.) and Magnolia (Magnolia sp.).
So, finally we arrive at the Modules.  This is a concept from Douglas Tallamy.  Modules are guilds of native plants that can be thought of as interconnecting “modular” units. They can repeat or interlock with other guilds by using the same edge species (understory trees most often).  It’s a great way to start visualizing just how we can start to restore native plants in the landscape one unit at a time.  Mr. Tallamy’s examples of modules will help (.pdf)
Tallamy hits the nail on the head in the first paragraph:  “Many people who have decided to rebuild native plant communities in their yards become quickly overwhelmed with the decisions that have to be made when it comes to selecting plants. For any given locality there are often dozens of possibilities; which ones are best? Which species work well together? Which are available in local nurseries?”
We’re trying really hard to answer that last question.  I hope that all this information has got you asking some questions of your own such as: “Is there room for a fruiting understory tree in my canopy?” or “What is a good shrub layer for the dry, shady hillside out back?”
Here are a few more references to boot:

Observation and Restoration

     I’ve been reading a number of books about permaculture recently.  For those not familiar, it’s a set of guidelines/principles that seek to integrate human settlements into the natural landscape and make them sustainable.  It’s still on the fringe of mainstream ecology and the scientific community has been hesitant to embrace it, and rightfully so, because it is more of a philosophy than a scientific discipline.  That being said, I think it is a step in the right direction toward changing the way that we view and interact with natural systems.

      The main tenet of permacultural principles that I think also meshes well with the scientific method is that of observation.  Only by observing intact, healthy ecosystems can we know how the natural world works to produce clean water, humus-rich soils, nutrient-dense plants/fruits, and how it cycles death and decay into life and sustenance.  Observation of the natural world can inform our decisions as to what plants belong where, and what species grow well together.  This hits close to home for us at Beech Hollow, as our entire operation is an attempt to place native plants back into the landscape, but if the plants are put in an inhospitable environment they will perish and all our work will be erased.

     In an attempt to inform ourselves, and later our customers and readers, as to the ideal environment in which to place the plants we propagate Pandra and I have decided to start visiting some of the intact fragments of the Piedmont’s varied ecosystems to observe just where each specie thrives.  Pandra gave me an excellent book for Christmas to guide us on this quest: Favorite Wildflower Walks in Georgia by Hugh and Carol Nourse. It has us planning excursions to numerous public lands in order to get a glimpse of what the landscape once looked like, and hopefully how we can mimic nature with our plantings .  I took a trip this past weekend to the Chattahoochee River National Recreation Area with a few friends to see if anything had started blooming yet.  The CRNRA is fully engulfed by the massive sprawl that is Metro Atlanta, and yet these small pieces of land survive relatively intact in their natural state.

       The hike I took was on the West Palisades Trail, which is within a mile of two major interstates, and surrounded by apartment complexes.  Despite the urbanization around it, this trail will transport you from what is essentially a parking lot for a giant apartment complex to a bend in the broad river teeming with birds and the only sounds you’ll hear are the wind and the water.  The bluffs across the river from this trail have their own trails system and rise about 300-400′ above the water, and in the summer months brave/foolhardy people jump from the lower bluffs into the frigid waters below as hundreds of kayakers pass through the shoals known as the Devil’s racecourse.  On a windy day in February the only life on the river was of the avian variety:

  In addition to this and other Blue Herons, we saw Canada geese on their way north, Mallard ducks courting on logs, and numerous sparrows and finches flitting about the wooded slopes.  The main reason for the hike was to see some plants, and despite it being early February, we were not disappointed.

Trout Lilies (Erythronium umbilaticum) were blooming by the hundreds on the steep banks.  Their tiny yellow flowers tend to blend in with the decaying fallen leaves, but once you see a few, the rest just jump out.  These tiny, delicate plants take many years to reach maturity and flower from the corms they form deep underground.

   We also saw several Trilliums (Trillium cuneatum) getting ready to pop open. These plants take seven years  to reach maturity and flower when grown from seed. Sadly, many populations of these beautiful, but slow growing plants have been dug up and collected over the years, and they just can’t replenish themselves in the face of such rampant theft.  Fortunately there are still quite a few that survive near this trail. 

 Look for pictures of these lovely, threatened flowers in the coming weeks as I return to observe and document the succession of spring blooms in this hidden gem of Atlanta.

Hugelkultur: Using Woody Debris in the Garden


           Atlanta and the surrounding metro area are blessed with an abundance of trees compared to other cities of similar size.  It’s unusual for a yard to not have at least a couple of trees shading part of it, which leads to the most frequently asked question at plant sales, “What grows well in shade?”  While most people are thankful for the shade that these trees provide from the summer sun, the thankfulness turns to irritation in the fall because the trees drop their leaves and dead branches.  Seasonal pruning of shrubs also creates piles of ‘yard waste’ that most people bag up and set on the curb.  There is another option for disposal of this material that will enhance your garden beds and return the nutrients that the trees and shrubs have removed from the soil back to square one, thus completing the nutrient cycle.

            Hugelkultur translates roughly from German as “mound culture” (so I’ve been told…) and was a common practice in Europe centuries ago.  It is a technique that is regaining popularity with permaculturists and gardeners because it mimics the nutrient cycling that naturally occurs in forests.  It also helps the soil to better retain moisture which reduces the need for supplemental watering of plants and helps them to survive prolonged periods of drought.  Trees and other woody plants naturally accumulate and concentrate minerals from the soil as they grow, so by incorporating woody materials back into the soil these minerals are released and made available to plant roots as the materials are broken down by soil microorganisms.  All-natural fertilizer, less watering, and healthy plants. Sounds like a win-win situation.

         A  hugelkultur bed can be started on the existing ground surface or can be partially buried depending on the desired final height.  The photos in my example are from a vegetable garden bed that I constructed in my back yard using 1) Branches from pruning back shrubs, 2) Fallen leaves and small branches from oak trees, 3) Partially composted kitchen scraps and 4) The topsoil that I dug out of the bed area prior to starting.  You will need some soil to cover the top of the pile, so if you want to start on the existing ground surface and end up with a raised bed you can either remove the top 2” of soil or find another area to borrow some topsoil.  The latter option is a necessity if you start on eroded or clayey soils that lack a good topsoil layer.  Once the necessary materials are gathered and the site chosen it’s time to get started.


          I made my bed outline 3 x 8’ because that’s how big my other raised beds are, but your bed can be any shape or size.  Rectangles are kind of boring, so don’t be afraid to get creative.


I saved the dirt I removed on a tarp so it would be easier to replace it once I finished.


          Once I started hitting clay I stopped digging.  I’m fortunate that my garden area has had 50 years or so to build up a nice layer of topsoil since the house was built, so I was able to go pretty deep.  Soil transition layers vary widely, but once you hit clay or mineral soil you should probably stop.


          Chopped up twigs, sticks, pruned branches, etc. go in the bottom of the trench.  This was my first attempt at building one of these beds and subsequent reading has made me wish I had put some larger diameter branches/logs on the very bottom. The larger branches have more biomass, will take longer to break down, and have the ability to hold more moisture than the small stuff I used.  C’est la vie. Next time.  Water down the woody materials well before proceeding to the next step.


          Partially composted kitchen scraps went on the wet branches.  This is what I had available, but anything with a high nitrogen content, such as fresh manure, alfalfa, green grass clippings, or coffee grounds will work. The fresher and greener the better.  My material was partially composted, so had lost some of that valuable nitrogen, but it was what I had on hand, so it was what went in. I drink enough coffee that it was probably 1/4 coffee grounds anyway, so I wasn’t too worried. The reason that high nitrogen material is needed is that the woody material is high in carbon, which is slowly broken down by fungi and microorganisms in the soil.  These decomposers need the easy to digest simple sugars and nitrogen in the green material to build their bodies and secrete the enzymes that allow them to break down the more complex carbon compounds in the wood. 


          Soil goes back on top.  That’s about 6-8” of soil, but as little as 1-2” would suffice.  Just enough good soil so that plants can have a healthy root zone to start growing in until they are able to tap into the bounty below.


            This is the bed as it is today with some pepper plants growing in it.  I surrounded the bed with several large sections of an oak branch that came down during a storm a few weeks after I built the bed.  It helped define the bed and prevent soil erosion during heavy rains.  The soil has settled considerably as the woody materials have broken down.

           My anecdotal evidence for improved moisture retention is that the pepper plants in this bed showed less leaf wilting than their counterparts in my other beds that are just straight soil on many hot summer afternoons.  We also utilize woody debris (often tree trunks) in the propagation beds at the farm and our plants there are doing great.  I see fungal mycelium strands running through those beds every time I weed or plant something new.  Fungi break down the wood, and in the process create vast networks of mycelia (think of them as ‘roots’ for fungus) that transfer nutrients and water throughout the area.  Most plants can “barter” with the fungi for nutrients in exchange for some of the sugars they exude from their roots.  Search for “soil food web” if you’d like to learn more about this fascinating process.       

           So, there you have it: hugelkultur.  Hard to spell, relatively easy to do.  A little internet searching will help you to find people and sites more knowledgeable on this subject than I am, but I hope this was a good introduction and has gotten you to think about reusing the woody debris that property maintenance inevitably produces.