Category Archives: Plants

Least Trillium lives on…

I’m happy to report that the Least (or Dwarf) Trillium (Trillium pusillum) that I feared had been dug up by the plant poachers (as an incidental effect of bluebell thieving) has escaped the spade for another year.

My Ornithology class looked down from the skies today and admired some of the wildflowers on Bluebell Island. The Least Trillium was in bloom. Hooray! The species is classified as endangered in Tennessee, so every plant matters. There is only one other location known for the species in our county.

Note that the annual land trust hike to the island is this weekend. (I’ll be out of town and will have to miss the event.) Land trust volunteer leaders will be on hand to help people across the log to the island (a fun challenge) and to point out interesting plants.


Thanks to Will Coleman and his iPhone for this shot.

Thanks to Will Coleman and his iPhone for this shot.

Over the winter I had some new signs made for the island. A few weeks ago Sanford McGee, Joseph Bordley, Bran Potter, and Bob Salter joined me in a little expedition to put them up. Hopefully the message is clear and people will leave the plants in place:


Dead wood, ashes.

One of Shakerag Hollow’s giant trees has fallen. An ash that until last week held its arms in the highest reaches of the canopy now sprawls across the forest floor, its body utterly torn. I’ll go back soon and “measure” things (how tall? what weight of wood came slamming down?), but for now: just awe.

I did not see the fall, but came by soon after. The trunk was … indescribable. Some grand words are needed, for barely imaginable violence had been at work. Rent asunder!? The whole wide trunk was twisted and split open, lengthways, in several long gashes. Other trees, themselves no mere saplings, were smashed into the ground. Large boulders were shifted as roots reared and cracked. The air was infused with the odor of fresh-split wood. An overtone of bitterness, like cut oak, but mostly a sweet smell, almost honeyed.

I found the tree in the morning and returned in later in the day for another look. As I stepped closer in the warm afternoon, I hesitated then held back. There were wasp-like creatures, big ones, swarming over one of the thick exposed roots. These insects were scurrying, flickering their wings, crawling over each other. A frenzy.

Black with bold yellow stripes. Buzzing as they flew. Had the tree fall unearthed a buried wasp nest?

Neoclytus caprea

But something was not quite right about these wasps. I moved forward slowly and saw their fat hind legs, too beefy for a wasp. Crickets? No. Then the wing cases, striped in black and yellow: beetles! Wasp-mimicking beetles of some kind. I moved to the side of the tree and saw hundreds of them, racing up and down the bark. They were on no other trees nearby. Half of the beetles were copulating; the other half seemed intent on colliding with the mating pairs. Even though I now knew that they were harmless, their waspy nature made me cautious. Even their short curved antennae were creepily hymenopteran in style (oh yes, those hymenoptera have style).

Who were they? To identify them, I spent some time in the online funhouse known as the Photographic Atlas of the Cerambycidae of the World. This is an amazing site devoted to a single family of beetles, the so-called longhorns (although many of them do not have long antennae). The family contains twenty thousand species, an impressive number when we remember that there are fewer than six thousand mammal species. Some of these cerambid beetles run afoul of humans when they bore into trees and wood that we’d rather they stayed out of. A few of them are “invasive exotics,” killing off native plants. But the beetles in Shakerag were natives: Banded Ash Borers (Neoclytus caprea (Say) 1824). They have an interesting life history, finding recently downed ash and oak trees, then laying their eggs in the bark. The larvae then chew on the wood below the bark, emerging next spring to start the hunt for a newly downed tree.

So I was not the only creature in Shakerag following my nose to the smell of ripped up wood. How many huge ash trees have fallen lately? Not many. Every banded borer within miles must have been at this party. Those flickering antennae are surely tuned to the chemical particularities of newly opened ash wood.

The beetles were one of the very first arrivals in the tree’s new existence. When a large tree falls, its ecological life still stretches out into the future. Perhaps half of the animals (and many more of the fungi) that the tree will nurture during its existence arrive after the tree has fallen. The ecological vitality of a forest can be judged by how may large trees are lying around, feeding beetles, hiding salamanders, growing fungi.

To paraphrase Mr. Faulkner, “Dead wood is never past, it’s not even dead.”


Shakerag Hollow snow

Winter seemed to be slipping quietly out of the door, but evidently it still has business here. The forest floor is transformed.


Where-ever dark objects protrude, they soak the sun’s weak heat. Gradually the surrounding snow sublimates, leaving sleeves of empty space around twigs and leaves.

SnowComp7The nascent growth of spring wildflowers is checked. Buds and furled leaves endure, listening for the click of the door.

This slideshow requires JavaScript.

Wrestling with privet on Bluebell Island

Sharp blades and muscles: These are the lab tools used lately by my class. We’ve been mapping and eradicating privet from Bluebell Island, a local hotspot for wildflowers. Privet is a non-native invader and it overshadows and kills native plants.

Setting up the mapping transect.

Setting up the mapping transect.

The View from Lazy Point used as a field clipboard. The class  combines field work with discussions of readings, so hardback books find multiple uses. I hope Carl Safina would approve.

The View from Lazy Point used as a field clipboard. The class combines field work with discussions of readings, so hardback books find multiple uses. I hope Carl Safina would approve of the students’ improvised use of his fabulous book.

This project started in 2001 when my Ecology class measured and mapped every privet stem on the east side of the island where the flower populations are concentrated. I repeated the project in 2007 with my Seminar in Ecology and Biodiversity, then this year with the Advanced Ecology and Biodiversity class.

We uproot the privet plants...

We uproot the privet plants. Easy to do when they are small…

...not so easy when they are big. Katie pulled this one by hand. All that work on the swim team has paid off.

…not so easy when they are big. Katie pulled this one by hand. All that work on the swim team has paid off. No need to pull out the saw.

We’re building an interesting dataset. There are not too many places where we have long-term data on the details of how invasive plants respond to attempts at control. Along with this scientific goal, we’re hoping to leave the island in much better shape for wildflowers.

What have we found? At first glance, the project seems to be failing spectacularly. There are many, many more privet plants within the project area now than there were in 2001.

Total number of privet stems increased over time.

Total number of privet stems increased over time.

But this graph does not capture the whole story. The vast majority of the stems in 2012 are tiny little sprouts, reaching to knee-height. In 2001, the stems reached over our heads and were casting dense shade.

The number of large plants has decreased over time.

The number of large plants (>15 or 30 mm in diameter) has decreased over time.

The average (mean) size of stems decreased over time. The graph also shows that the variability in stem diameter (standard error of the mean) also decreased over time.

The average (mean) size of stems decreased over time. The graph also shows that the variability in stem diameter (standard error of the mean) also decreased over time.

So we’ve lost big plants and gained lots of little seedlings. It seems that the removal of large privet plants allows light to reach the ground which encourages both wildflowers and new privet plants. Long term success will depend on continued visits to the island to stop new privet sprouts from getting too big. The rest of the island, outside the study area, serves as an interesting contrast. It is overrun with large privet plants and the wildflower populations are dying out. Eradication of privet over the whole island would be a more major undertaking than could be accomplished by one class, even with many days’ work. Fire and goats might help.

Tyler Johnson prepared this map of the location of every privet stem (2007 data) in Dr. Chris Van De Ven's GIS class. We'll be expanding the mapping analysis in coming months to include all three sapling periods, examining whether the spatial distribution of privet has shifted over time.

Tyler Johnson prepared this map of the location of every privet stem (2007 data) in Dr. Chris Van De Ven’s GIS class. We’ll be expanding the mapping analysis in coming months to include all three sampling periods, examining whether the spatial distribution of privet has shifted over time.

Bluebell Island is owned by the South Cumberland Regional Land Trust and was bought with contributions from naturalists in Sewanee and beyond. It hosts dense populations of bluebells, trout lilies (including white trout lily), and even the rare dwarf trillium. I’m grateful to the SCRLT board for their continued support for this work, a project that started when I served on the board but has now extended for more years than I at first imagined.

Privet is not the only threat to the island’s famous wildflower display. Gill-over-the-ground is another non-native plant species that has made inroads on the island, as has exotic honeysuckle. In addition, poachers have dug significant numbers of plants over the years. About ten years ago they hit the island so hard that many parts looked as if they had been rototilled. The bluebells gradually regrew. This year, the trespassers hit again, digging large patches. I’m pretty sure that one of these patches encompasses the only known plant of the dwarf trillium in this part of Tennessee, so this rare species may now be extirpated from the island. The poachers are targeting bluebells, but the tiny trillium plant got taken as collateral damage. I may be wrong – we’ll know in the spring – but the digging crosses the exact spot where the plant lives. So if you’re tempted by the pretty bluebells for sale at the nursery, I’d advise you to skip them unless the seller can prove to you that they were nursery-propagated.

Despite the pressures, Bluebell Island is still a marvelous place. In addition to the flowers, old trees provide great habitat for woodpeckers, owls, and wood ducks. Beavers and mink swim the river. Migrant birds ply the riverbanks in the spring. Butterflies are abundant in summer. The river itself is different on every visit. It runs clear and calm in winter dry spells; swells silty and trashy in the floods; then courses bluegreen in the warm algal summer months. Suwannee is a river, but Sewanee is not; so I enjoy my visits off “the mountain” to see some real flow.

Beavers came around after us and snacked on the discarded privet stems.

Beavers came around after us and snacked on the discarded privet stems.

I’m grateful to the many cohorts of Sewanee students who have yanked, sawed, tweaked, measured, mapped, and analyzed these thousands of privet stems.

Sewanee's Bio 315 class in "gaze at the sun as if something inspiring and important was happening" pose after pulling 4275 privet stems. The largest vanquished stem is held as a trophy. We omitted the blooding ceremony.

Sewanee’s Bio 315 class in “gaze at the sun as if something inspiring and important were happening” pose after pulling 4275 privet stems. The largest vanquished stem is held as a trophy. We omitted the blooding ceremony.

Sourwood in bloom

Most local trees bloom in the spring or early summer, but sourwood (Oxydendrum arboreum) waits until summer is well underway to grow its graceful clusters of small white flowers. These clusters arch out from the tips of twigs and, although each flower is quite small, the mass of flowers is visible from some distance. Bees love the nectar of this tree and in places where sourwood is plentiful “sourwood honey” is considered a fine complement to a slice of bread (I’m afraid that my bee-keeping knows no such temporal precision — whatever the bees gather over the course of the summer is what I get in the jar).

Sourwood is something of a botanical misfit. It grows as a small tree, yet its closest local relatives in the “Heath” family (Ericaceae) are all shrubs or tiny herbaceous flowers: mountain laurel, blueberry, azalea, wintergreen, and so forth. Like these kin, sourwood grows mostly on poor, acidic soils and relies on symbiotic fungi to help its roots find nutrients in these challenging conditions. Sourwood doesn’t quite fit with the “trees” either. Even when full grown, it is never as large as the oaks and hickories with which it grows; its trunk is seldom straight, usually leaning to one side; and, like its cousins the shrubs, it often sprouts more than one stem from the base.

The kinship to blueberries is evident in the flowers which are shaped like urns or bells. Unlike blueberries, sourwood fruits are, unfortunately, mere dry capsules.

“Under the spreading chestnut tree…” (via telescreen)

Hill Craddock and Tom Saielli visited Sewanee today with four hybrid chestnut trees to plant in our forest. Hill is in the Biology Department at UT Chattanooga and has worked for many years on American chestnut breeding and restoration; Tom is the Southern Regional Science Coordinator for the American Chestnut Foundation.

Photo credit for this photo and all others in this post: Buck Butler. Thank you, Buck!

Some backstory: the American chestnut (Castanea dentata) was formerly one of the dominant trees in our region, comprising half of all the trees in many forests. In some places the species grew in pure stands, a fact that is commemorated in many place names (Chestnut Ridge, Chestnut Hollow, etc). Chestnuts produced annual crops of tasty nuts and many animals depended on this massive burst of autumnal nutrition to make it through the year. In the late 1800s a fungus (Cryphonectria parasitica, an ascomycete) came into the U.S. on trees (of another chestnut species) imported from Japan. The fungus spread from the New York City area across the entire Eastern U.S., wiping out chestnuts as it went. From about 1900 to 1940, almost every tree was killed. The ecology of our forests was forever changed; other trees increased in abundance and many animal populations undoubtedly declined significantly due to the loss of the chestnut crop. These changes took place at the same time as the forest was being hit hard by unsustainable logging and grazing, so these were not happy decades for woodlands.

These days, the chestnut survives in the wild mostly as scattered small trees that grow for a few years, then get knocked back to their roots by the fungus. The fungus also infects scarlet oak, an unfortunate state of affairs because scarlet oak now acts as a continual reservoir of spore-producing fungus ready to attack chestnut saplings. A few large trees survive, either through luck or through the presence of a fungus-weakening virus that keeps the infection in check. But in the big ecological picture, the tree is functionally extinct.

All may not be lost. For many years now, scientists have been crossing the American chestnut (obtaining pollen and nuts from a few survivors) with the Chinese chestnut, a different species that is more resistant to the fungus. The resulting hybrids are indeed resistant to the fungus, but they have many characteristics of the Chinese parent that make them unsuitable for becoming true ecological “substitutes” for our lost Americans (e.g., their growth form is more bushy, they are more vulnerable to late freezes, etc). So, these hybrids (F1s, in biological lingo) are back-crossed to the American chestnuts for several generations (summarized here). These crosses produce plants that are nearly all American, with a few Chinese genes thrown in. The important step is then to pick out the offspring of these back-crosses that are truly disease resistant. This is where the trip to Sewanee comes in. Only by placing thousands of back-crossed seedlings in the forests, then testing them for disease resistance, can we ascertain which trees have inherited the right combination of genes.

So today we planted four seedlings in an area that had previously been cleared of planted pine. We hope in the future to establish a larger test area with hundreds of seedlings. The seedlings today were B3s — meaning that they are the result of three generations of back-crosses.

I’ll close with thanks to my colleagues Nate Wilson and Ken Smith who arranged for this visit and planting, and to Hill (in the green shirt above) and Tom for sharing their plants, their expertise, and their good cheer.

Spotted Wintergreen

This diminutive wildflower grows in sandy poor soils. It also goes by Pipsissewa, from a Native American name (which of the many languages of Native Americans, I do not know). The leaves taste vaguely medicinal and were once used in root beer.

The flower stands about five inches tall. This one was growing below the cliff at Morgan’s Steep. I angled the camera up to give a bumblebee’s view of the ornate architecture of the flower — these insects are the main pollinators.

Junebug bombed the photoshoot. Stasis and motion:

The plants are growing in deep woodland shade and the white stands out from the gloomy surroundings like a tiny bumblebeacon.

Pricky Pear in bloom

Tennessee’s only native cactus, the prickly pear (Opuntia humifusa) is coming into flower. The flowers stand on top of the fleshy green stems like torches on monuments — an apt comparison in both shape and brilliance of color. The gorgeous intensity of orange and yellow in these flowers is hard to convey. Wow. I feel my wax wings start to melt.

This cactus grows in places that are too hot and dry for most other plants: rocky outcrops, dunes, gravel, and thin rocky soil. I found this cluster of plants on the lichen-encrusted sandstone outcrop behind the Fulford Hall parking lot in Sewanee. There are dozens of cactus plants there, each one bearing several flowers. I’ve never seen such profusion. Perhaps the long warm spring has suited them.

Bumblebees love the flowers. Such is the strength of their desire that several were fighting their way down between the petals of unopened flowers. Later this summer I’ll check the patch again. The pulp of the fat red fruits is edible, although the spines urge caution in this gastronomic quest.

Mountain laurel pummels bees

Mountain Laurel (Kalmia latifolia) is in bloom on the dry ridges and steep slopes around Sewanee.

Its closed blooms look like piped icing:

And open to reveal purple and pink within:

The center of each flower has a pollen-receiving pad, the stigma, surrounded by ten filaments that curve out from the center. At each filament’s tip is an anther, a little purple pouch of pollen. These anthers are lodged inside pockets at the edge of the flower. The filament elongates as it grows and pushes against this pocket. When a bee lands on the flower, the anther is jostled out of its pocket and the tension in the filament causes the anther to spring upward, slapping the bee with a dusting of pollen. You can mimic this action by prodding the anthers with a small twig. The pollen shoots out for several inches. Very amusing, I find. If no bee or human comes along, the anthers will eventually rise up and dust the stigma with pollen, ensuring fertilization.

Skullcap and Catchfly

I ran into a small cluster of Showy Skullcap, Scutellaria pseudoserrata, on the trail that winds through a dry upland oak forest in Sewanee (for local readers: the perimeter trail, north of the memorial cross). This wildflower grows about a foot fall and has pearly-purple flowers at the top of a slender stem. It was the only herbaceous plant in bloom under the forest canopy. The dry upland woods don’t support the profusion of flowers found in the moist coves, so the these skullcap flowers are visually striking in the otherwise green understory.

The tube leading from the lip of the flower down to the nectar the flower’s base is very long, excluding all but the longest-tongued bees and moths. Keeping the nectar relatively inaccessible saves the plant from giving nectar to insects that are poor pollinators (e.g., ants), but it also means that in many years no pollination takes place at all. In the closely related large-flowered skullcap (S. montana), a study by Mitchell Cruzan from the University of Tennessee reported that “several hundred hours of observation over four seasons suggest that these pollinators may be rare or lacking.” Most flowers either produce no seeds, or self-pollinate. This seems like a dreadfully slow way of propagating the species, but these plants are perennial, coming back year after year, so they don’t have to spew thousands of seeds into the world each year to pass along their genetic legacy. A more open flower might attract more insects, but the costs of such a flower design (wasted nectar and visits from insects that will not visit another skullcap) may outweigh the benefits. Or, an undocumented decline in the local moth and bee populations has left this species high and dry. No way to know for sure.

[Thanks to Mary Priestley and Jon Evans for helping me sort out the difference between pseudoserrata and montana. The latter is found just to our east and has leaves with velvety short hairs all over its upper surface. The species is listed as “threatened” by the USFWS.]

Further along the trail, out of the woods in a tumble of rocks on the cliff edge, I found another showy flower, the Roundleaf Catchfly, Silene rotundifolia. This species’ leaves and petals are covered with sticky secretions that snare wandering insects, keeping them away from the flowers’ nectar. This stickiness also catches crud and dust, giving the plant an untidy, unwashed appearance. My Horn et al. wildflower book (an excellent guide in almost every way) tells me that “flying insects” are the pollinators, but I doubt that. The bright red flowers, splayed open and pointing skyward, strongly suggest that hummingbirds are what the plant seeks. A quick search on the web confirmed this suspicion, at least for the look-alike Silene virginica.