Thoughts on Plots

Carex swanii

By Ezra Staengl

June 7th, 2020


One of CUH’s most powerful tools for understanding plant communities is the vegetative sample plot.  Plots allow us to identify the plant community and quantitatively assess its health.  In a restoration setting they can be used to track changes in a plant community over time.  I used to think restoration plots were some of the most boring work I did as part of the CUH survey department.  While they’ll probably never compete with the fascination of surveying a healthy example of a plant community, I’ve come to see that there is incredible value in doing plots in degraded landscapes as well.  Even in the most impacted plant communities there’s often a hint left in the vegetation about what used to be, and what could be again.  Finding that hint and using it to extrapolate the associated plants and plant community is central to the importance of restoration plots.  No less important and exciting is that repeating the same plot multiple times through the years provides quantitative measurements of change.  It’s often obvious that a plant community is changing for the better through restoration work but being able to see that change numerically through plot data collected at different times is fascinating.

When we do plots, we use a method that closely resembles that used by the Virginia DCR’s botanists, so our data is comparable.  Our plot size is 400 square meters for forests and 100 square meters for grasslands. We inventory all woody layers of the plant community thoroughly, counting and recording diameter at breast height for all individuals, and documenting and recording cover class for all species present.  Cover class is an estimate of the total ground area within the plot covered by a given species.  For the herb layer we just record all species present and their cover classes, because counting each individual is almost always impractical.  We also collect physiographic data about the abiotic elements of the community such as elevation, aspect, slope, landform, geology and soils, which in combination with the plant data allow us to “identify” the plant community.  We then use two formulas to calculate diversity and exotic species importance from the cover class data.  Diversity in an ecological sense is a measurement of evenness of abundance, not species richness.  A plot with only four species that each occupy the same amount of space might be more diverse than a plot with 40 species, if only a handful were dominant.  Diversity doesn’t take into account exotic species prevalence, so exotic species importance is an interacting value that suggests how much of that diversity is actually native.

I recently did a plot in my family’s garden, in the very northwest corner of the roughly 2/3 of an acre clearing my house is located in.  It’s certainly not a phenomenal plant community, but it is the area at my house that seems to have the best chance of naturally resembling a healthy Piedmont prairie in the near future.  It’s been relatively open for a long time (how long exactly I don’t know), and continually disturbed in a variety of ways since my family bought the house six years ago.  When we bought the house there was an old gravel driveway going through the area, and it was used as a horseshoe throwing pit.  Now it’s mostly a thicket of calico aster (Symphyotrichum lateriflorum), tall goldenrod (Solidago altissima) and Pennsylvania blackberry (Rubus pensilvanicus), but other prairie species, particularly common flat-top goldenrod (Euthamia graminifolia) and slender-stemmed panic grass (Dichanthelium acuminatum var. fasciculatum) lurk in there as well.

I found 63 species of plants in my plot, which isn’t a lot for a healthy grassland, but is still impressive for an abandoned corner of my family’s garden.  Diversity was relatively high, as was exotic species importance, suggesting that while different species of plants are reasonably equitably distributed within the plot, exotic species make up a large portion of that diversity.  Over the next several years I intend to remove exotic species and perhaps introduce other native prairie species from local native seed sources.  In the future, I’ll repeat the plot so I can quantify how the plant community continues to change.  I can’t wait to see if it looks different in a few years!