Pin the Plant on the Triangle

This semester, one of the classes I’m teaching is herbaceous plants, and I’m taking the class beyond the usual discussions of annuals and perennials.  From studying herbaceous plant communities, one of the most useful concepts that I’ve learned in recent years is the classification of a plant’s survival strategies.  

I’ve written about it before here and here.  As a refresher, Grime pitched that plants had three strategies based on environmental factors.  

• COMPETITORS are plants that take advantages of any and all resources they can muster.  They grow tall and wide to take out the competition.  Usually these stalwarts are perennial in nature, and they grow where stress and disturbance are nil.

• STRESS-TOLERATORS are plants that have adaptations to ensure survival when stress arises and conditions deteriorate.  They are usually perennial and can take many years to flower from seed.

• RUDERALS are short-lived annuals or biennials that are frequently exposed to some type of disturbance, which has selected for plants that quickly produce seed.

Usually, this strategy is visualized using a triangle (much like the soil texture triangle!) where a certain species can be shown to be—pulling some numbers out of the air—say, 70% competitor, 20% ruderal, and 10% stress tolerator based on the characteristics they exhibit.  

A figure of Grime’s triangle from Pierre et al. (2017) titled A global method for calculating plant CSR ecological strategies applied across biomes world-wide. As you can see the authors attempted to classify plants across the globe based on their tendency to be a competitor, stress-tolerator, or ruderal.

How do you take this concept from theory to application for students? Much research and data collection is needed to be able to precisely place a plant on the triangle.  Can it be done in a more simple fashion?  

After we covered the CSR theory in class, I did an activity with students.  I gave small groups (three to four) a list of seven different herbaceous plants and asked them to look up information and pictures online and try to determine where on Grime’s triangle it would fit.  I drew a triangle on the board labeling the sides and gave them markers and half sheets of paper for writing plant names.  

I then challenged them in pin-the-tail-on-the-donkey fashion (no blindfolds or sharp objects though!) to figure out where on the triangle the species would go by searching for it online.  Students looked for tendencies to spread, cover large areas, form large clumps, and/or have rhizomes (COMPETITOR); tendencies to produce copious amounts of seed, occur in areas of disturbance, and/or be short lived (RUDERAL); and tendencies to live in a stressful habitat, take a long time to flower, and/or have storage organs (STRESS-TOLERATOR).

One by one they started coming up and making educated guesses.  I stood by the triangle to offer advice and suggestions.  Some hit the nail on the head while others needed a little bit of coaxing to the right place.  

At the end, we went over the 20 or so species I provided as a challenge.  Again, I explained that while some species neatly fit into one group, some straddle the fence like Liatris elegans.  It has a corm (a stem-derived storage organ indicating some level of stress toleration) yet produces copious amounts of seed (traits of a ruderal).  

Pin the plant on the triangle—a fun game to teach students about plant survival strategies. Based on your plant knowledge, how do you think they did?

As gardeners it’s very helpful to think about flora in this way.  It helps us anticipate how plants will perform.  It explains why Gaillardia and Aquilegia don’t live long as perennials (ruderals), why Mentha and Monarda spread like crazy (competitors), and why Trillium and Narcissus  take 3–7 years to flower from seed (stress-tolerators).   It also allows us to envision how to combine plants.  Maybe put that runaway competitor in a drier spot to keep it from taking over creation?  Or, sow some ruderals in between the stress-tolerators to keep weeds down.  

If students can decide approximately which section of the triangle plants fit in during a 15 minute activity using search engines, then we can by watching how plants grow over the course of a year. 

So, that’s your homework for the season. Draw a triangle and see if you can’t plot where the species in your garden fit.

A Pioneer in the Smokies

The Smoky Mountains are a magical place for me.   Always have been.  Always will be.  Probably once or twice a month I have dreams where I'm driving along the twisted roads or hiking the fabled trails.  It's my parents' fault.  They took my sister and me there when I was nine, rolled down the window, and herded clouds into the car on the high mountain tops.  I was hooked.  

I like to visit the mountains once a year or so, and last spring, Karen and I planned a visit to the Great Smoky Mountains National Park over my long Easter break.  I, of course, started searching for great places to see wildflowers, and reports for Greenbrier suggested it was peak for early spring bloom.

Greenbrier is no stranger to me.  It's one of my favorite places to visit.  When I was in grad school in Raleigh and met my family for a long weekend in Gatlinburg, I'd always pass Greenbrier on Highway 321.  Sometimes if I was a bit early, I would stop and say hi to the craggy creek.  

The Little Pigeon River gurgles through Greenbrier.

For this visit, we would be staying a bit longer in Greenbriar to hike Porters Creek trail.  I had seen pictures online of the Phacelia fimbriata (fringed phacelia) in full bloom, and the effect looked incredible, like a carpet of white wildflowers in the woodlands.     

We parked for the day along the car-crowded road, which suggested we wouldn't be alone for the hike.  We walked for about an hour passing old stone fences and traversing mighty hemlocks.  We hadn't seen many flowers in bloom till we came to a narrow bridge.   

The narrow bridge along Porter's Creek trail.  Hikers provide a sense of scale.  

However, once we crossed over, it felt a bit like entering Narnia because suddenly we were surrounded by snow!  

Where's the lamppost?!

Ok, green and white snow.  But, it was everywhere!!!  

Phacelia fimbriata o'er hill and dale

And, it continued for about a quarter of a mile.  It was breathtaking to see so many of one organism en masse.  

A moss-covered log rests in a blanket of Phacelia

Some of it even grew on rocks.  

Fringed phacelia thrive on a boulder, no doubt supported by a layer of detritus and abundant rainfall during the winter and early spring.  

A close up of Phacelia fimbriata.  The flowers were about the size of a dime.  

Much like footsteps on fresh fallen snow, a trodden path manifests through the Phacelia.  

In horticulture design we discuss how the effect of repetition is calming and creates harmony in the landscape.  In fact, just a few weeks ago I shared with my class that seeing the same plant used multiple times in the landscape creates a sense of comfort.  Much like when you travel to a foreign place and see familiar logos or icons. 

So, why so many of one organism?  No human planted this monoculture.  This is nature. 

From my environmental biology background, I learned to ask the question why does a species grow this way?  There have been efforts to classify plants based on their survival strategies, and Grime's universal adaptive strategy theory groups plants broadly into three different categories.  

• COMPETITORS are plants that take advantages of any and all resources they can muster.  They grow tall and wide to take out the competition.  Usually these stalwarts are perennial in nature.

• STRESS-TOLERANTS are plants that have adaptations to ensure survival when stress arises and conditions deteriorate.  They are usually perennial and can take many years to flower from seed.  

• PIONEERS (aka RUDERALS) are short-lived annuals or biennials that are frequently exposed to some type of disturbance, which has selected for plants that quickly produce seed.  

Like most human-made models, plants don't fit neatly into these classifications.  Most plants are a blend of at least two strategies, much like you see below.  

This figure from Pierce et al. (2013) illustrates how one can classify plants as competitors, stress-tolerant, or pioneers/ruderals.  The placement of the symbol equates to what percentage of each strategy each plant exhibits.  

But, thinking about these survival strategies can help us anticipate how plants will perform over time in our gardens.  They help us understand why stress-tolerant Trillium can take several years to flower from seed, or why pioneer Gaillardia can die in our gardens after a few years.  (If you want to read more about Grime's theory, might I suggest Planting in a Post Wild World by Thomas Rainer and Claudia West and Garden Flora by Noel Kingsbury).

In the case of the Phacelia that surrounded us on Porters Creek trail, we were looking at a pioneer-type species based on its short life span and the sheer abundance of plants.  Phacelia fimbriata is a winter annual.  It germinates in the fall, flowers the following spring, and dies after spreading seed.  It also takes advantage of the full sun that filters through the barren canopies during winter and early spring.  

This environment doesn't match my traditional concept of a pioneer species before I learned of Grime's theory.  I usually associate pioneers with species that come in and colonize an area after all vegetation has been removed, and yet around us were towering trees clambering toward the climax community.  But, as Larry Weaner and Thomas Christopher discussed in Garden Revolution, sometimes disturbance only affects a layer of vegetation and not all plants are removed.  

As I began to ponder what disturbance the Smokies get, my mind immediately went to the horrible wildfires that ravaged Gatlinburg this past fall.  Research in the Smokies has shown that fires on average have happened once every 5 to 7 years between the early 1700's to about 1930.  If this pattern was the same for millennia before, it's easy to see how this species evolved to survive frequent disturbance.  

We also encountered a few other spring ephemerals along our hike, and many were like old friends.  I hadn't them seen in a while, but they still brought a smile to my face.  

Dicentra cucullaria (Dutchman's breeches). See the hole? Looks like someone forgot to patch their pantalones before hanging them out. 

Trillium grandiflorum in all its grandeur.  

The freckled petals and coffee-colored stamens of Erythronium umbilicatum (dimpled trout lily) are a delight in spring.

Anemonella thalictroides (rue anenome) occasionally dotted the forest floor.

I assumed before we went that we would see Sanguinaria canadensis (bloodroot) everywhere, but I only saw one in flower.  It was actually right as we were coming back to the parking lot.  

Overall, Porters Creek trail was a great hike, and we both enjoyed the beauty of the spring wildflowers.  But, the wildflowers weren't my only goal for the trip.   

I also had plans to propose to Karen the next morning after the Gatlinburg Easter sunrise service.   She said yes, and the Smokies became even more special for the both of us.