Exploring the Talus of Turk

Today the Explorer’s Club went on an expedition in search of a rare tree. Nicolas, Julian, Luke, Keith and I set out to find the rare habitat that might harbor such a tree. We were looking for a true relic, a left over from a time that was much colder.
The trees we were after were:

  • Mountain paper birch, Betula cordifolia
  • Paper birch, Betula papyrifera
Both trees are rare in Virginia and finding just one is a real discovery. The mountain paper birch is an Appalachian species related to the paper birch of the north. There are very limited populations of this cold climate tree, and it has very specific habitat requirements. The paper birch (Betula papyrifera) is extremely rare in Virginia. In fact, its existence south of Pennsylvania has not been confirmed (as far as I know). Finding B. papyrifera would be extraordinary, a true botanical treasure.

Before our journey began we met in the parking lot at Turk Mountain Gap. We covered basic safety guidelines, including black bear, yellow jacket, and timber rattlesnake avoidance. We also pondered the qualities that a habitat would need in order to harbor a cold climate tree, a tree of northern latitudes. The group decided that high elevation, north-facing slopes, and exposure were the primary important factors.

I introduced the term “scree” to the group (it was introduced to me by Chip Morgan): an accumulation of rock fragments at the base of mountain cliffs. "Talus" is another word used to describe heaps of rock at cliff bases, but it refers to bigger rocks. A talus slope is one with large rocks and boulders, and scree is typically used by geologists when describing slopes with smaller rock fragments, pebbles and sand. We quickly reviewed the geology of the mountain. Basically, it is beach sand that has been metamorphosed. It is a very weather resistant white quartzite. Much of it is quite glassy, and later in the hike we got to listen to the talus slope sing and echo as we traversed its singing rocks. The talus slopes at Turk Mountain are a deep and layered heap of quartzite boulders and flat rocks, all having moved, at some point, down slope. These gigantic boulders clearly have not moved in a long time, and must have been heaved by some freeze-thaw force not present today. I imagine that this landscape was shaped by freeze-thaw action during the last ice age.

Might the talus slopes harbor ice into late spring, creating ideal microclimates for northern species? One hypothesis is that these slopes hold great amounts of frozen water in the winter. The talus slopes on north facing slopes may release moisture slowly from their complex web of cracks, nooks and crannies. This slowly melting ice may be responsible for creating the cool microclimate needed to harbor the paper birch. The cold air may creep down these slopes and meet the forest at the base of the talus. So, it is here that we should find paper birch...at the base of large north facing quartzite talus slopes. This predictive model has been very accurate for finding northern species (as demonstrated by the innumerable discoveries of Mo Stevens). Would it help us on this outing? We would try. Off we went in search of a north facing, high elevation, quartzite talus slope.

Skolithos trace fossils (ancient worm holes made in what was once beach sand).

We made a quick climb to the summit of Turk Mountain (2981 ft), passing through a fire impacted forest of mostly chestnut oak. On the crest we were welcomed by Canadian serviceberry, mountain holly, pitch pine and black gum. The rocks around us displayed magnificent trace fossils of the tubeworm Skolithos. It was easy to imagine beaches as the rocks were clearly composed of a bright white sand. It was more difficult to imagine the spot we were standing being lower, at sea level that is. The land was also turned so that today's east was south, and the spot we were standing on was south of the equator. I know, complicated. Check out this map for a visual (find Virginia if you can!): http://jan.ucc.nau.edu/~rcb7/namPC550.jpg

Upon reaching the craggy summit we climbed upon the highest protruding rocks for an astounding view. Wow, what a day. We could see, with ease, the Shenandoah Valley stretched out before us and the Allegheny front standing strong to the west. Standing here at this summit two months ago, Chip Morgan shared his knowledge of how the paper birch trees could be found. He encouraged me to use binoculars to search for them at the base of the talus slopes, which I did. In complete amazement to both of us, I spotted what I thought was a paper birch tree. I did not get to investigate that tree on that occasion, as the talus slope that had to be traversed was much too challenging on a day that we were already planned to explore another site. It would have to wait.

This tree spotted in Chip’s binoculars would be the first target of today’s outing. After refueling with water we climbed down the quartzite cliff and slowly made our way across the enormous boulder field. The sounds of the lichens on the rock combined with the crisp clinking echos from the bowels of the boulders created an auditory experience that can be repeated nowhere. We marveled at the endless deep and tiny caverns beneath us and imagined the multitude of timber rattlesnakes that must call that talus slope home. After some swift but careful footwork, we found ourselves at the bottom of the talus slope. It was there that Nicholas found a conspicuous piece of bark on the ground. There it was! A tree with papery white bark!Having confirmed the binocular sighting from earlier in the year, we began a thorough investigation of the habitat and the tree. We need to do two things: Figure out which species it was Document the plant community it was part of. After examining several randomly selected leaves and scanning the upper reaches of the tree we concluded that this tree was Betula cordifolia. The primary attributes that distinguish this tree from Betula papyrifera are the number of veins in the leaf and the base of the leaf. In this tree the there were between 9-12 pairs of veins on each leaf. The vast majority of leaves had heart-shaped leaves. Botanists call this cordate, and you can see where this tree gets its scientific name (B. cordifolia…cordate foliage).

Having confirmed the species we began noting neighboring plants. The plant community was quite sparse. Moving from the upper canopy down to the ground we observed: black gum, black birch, red maple, chestnut oak, Canadian serviceberry, American chestnut, mountain laurel, mountain holly, American witchhazel, False azalea, lowbush blueberry, and Virginia creeper. The slope of this habitat does not face due north. In fact, it faces 20 degrees West of North (magnetic).

After a successful inquiry at the mountain paper birch site we decided to begin our hike back to the parking area. We took a route that traced the edge of the talus slope to increase our chances of encountering more rare birch trees. While walking that through the wooded talus slope, Keith caught a glimmer of bright white through the trees downslope. It was another separate quartzite boulder field. We made our way to its upper edge and noticed a bit of white in the branches hidden amongst the foliage of the forest at the bottom of the slope. So, we did it again, down hill across boulders and flat rocks that clink, sing, echo and dance beneath feet. It was here, on a slope that faces more directly North, that we hit the jackpot.
There were two large multi-trunked paper bark trees in front of us. Almost immediately we noticed a significant difference between the leaves of this tree and those of the Betula cordifolia we found earlier. Its bark was chalky white, and none of its leaves were heart-shaped. These leaves had truncate or cuneate bases, and upon closer inspection, the viens in the leaves occurred typically in pairs of 6-9. Betula papyrifera! Another notable difference was that the new growth of stems and leaves on this tree was covered with fine hair (pubescence). Indeed, I believe we have discovered Betula papyrifera at this site. This site is the second I have seen this year in the Central Virginia Blue Ridge (the first being 3 miles to the northeast in a very similar habitat). How interesting to have both Betula cordifolia and Betula papyrifera on the same mountain!

With this discovery under our belts, we continued east in an effort to intersect the Turk Mountain trail. We passed massive black birch trees rooted right in the middle of talus boulder fields. These trees must be very old. We contemplated the meanings of the words “Virgin Forest” and “Old Growth” and considered the fact that outcrops and talus slopes present habitats that are frequently “Virgin”, that is, they have not been severely impacted by humans. We pondered the eons through which many of the lichens and mosses nestled on and between the rocks must have lived. We considered the possibility of some of the gnarled black birch trees being old growth trees, as they surely would not have been harvested for their twisted wood! We passed several enormous chestnut oaks, also well healed among the talus. How old are these trees? Surely the exposed mountainside and the poor nutrient soils have stunted their growth. Surely these trees are ancient!? This is an inquiry that will have to wait until another visit.

We eventually found our path and ate wild blueberries as we hiked back. We also found an area where owls were eating luna moths (wings on the ground). Just before exiting the woods we encountered a very excited family. They had just seen black bear cubs. They pointed the way and sure enough, we were able to observe a black bear cub resting in a tree. Sounds from the thicket below made it clear that mama was there as well, so we moved on up the trail. All in all, it was an amazing day of discovery. What a world it is up there on the top of that Blue Ridge!