Rock Point Inventory - Hem of the Woods

Stand of hemlock, patches of moss indicating exposed bedrock (Dunham dolomite)

So it begins, my documenting of the plants of Rock Point, that is. Realizing I'd miss the early spring ephemerals, I thought I'd just start with the patches with lowest diversity and the ones that I'm most familiar with, before covering the rest of the property. I hope to finish these other patches by next summer. I spent a couple of hours this morning wandering around in my first area, which we call Hem of the Woods SW. Hem of the Woods is almost entirely hemlock in the overstory with very sparse cover in the understory. It is bordered to the NE by an artifical slope excavated out for the Island Line - now the bike path, the lake to the W, and a mature sugarbush along its southern border. Much of the diversity of plant life here is found at the borders or in breaks in the canopy.

Stand of wild sarsaparilla in foreground, growing in shade of a couple recently
downed hemlocks (one massive). Birch is relic of older logging

In one such sunny spot at the intersection of two trails where a few trees were cleared out (stumps remain as evidence), flowering plants thrive. In Hemlock Forests (yes capital H and F, see Wetland Woodland Wildland for the reference), flowering plants are incredibly uncommon. The anomalously high number of flowering plants in the understory can be attributed to the small size of the patch. In most cases, the understory vegetation is represented by small clumps of a single species, most of which can spread rhizomatically (e.g. posion ivy, rock polypody, false Solomon's seal, Canada mayflower). The seedlings are represented by an abundance of black cherry, a single basswood, occasional sugar maples, and several Norway maples, surprisingly. Shrubs were not abundant, and include glossy buckthorn, honeysuckle and red elderberry.

Doll's eyes flower stalk

The two main limiting factor at this site are sunlight and shallow soils on calcareous bedrock. Lack of sunlight is controlled by the existing canopy in addition to a northern aspect. Where the deltaic sandy soils from the Champlain Sea era have eroded away with the occasionally flooding of the intermittent stream, Brick's Brook, the canopy is still composed of hemlock.

Red baneberry growing adjacent to doll's eyes. Note the much thinner stalks that the flowers grow from

Below is a complete list of all the vascular plants I saw, except for the ferns (* = non-native).

Trees + Shrubs

Hemlock, Eastern	Tsuga canadensis		Pinaceae (Pine)
Maple, sugar	Acer saccharum		Aceraceae (Maple)
Birch, white	Betula papyrifera		Betulaceae (Birch)
Basswood, American	Tilia americana		Malvaceae (Mallow)
Hophornbeam	Ostrya virginiana		Betulaceae (Birch)
Buckthorn, common	Rhamnus cathartica	*	Rhamnaceae (Buckthorn)
Thimbleberry	Rubus odoratus		Rosaceae (Rose)
Cherry, black	Prunus serotina		Rosaceae (Rose)
Maple, Norway	Acer platanoides	*	Aceraceae (Maple)
Dogwood, alternate-leaf	Cornus alternifolia		Cornaceae (Dogwood)
Ivy, poison	Toxicodendron radicans		Anacardiaceae (Cashew)

Flowers

Mayflower, Canada	Maianthemum canadense		Liliaceae (Lily)
Hepatica, round-leaf	Hepatica americana		Ranunculaceae (Buttercup)
Jack-in-the-pulpit	Arisaema sp.		Araceae (Arum)
Wild sarsaparilla	Aralia nudicalis		Araliaceae (Ginseng)
Jewelweed, spotted	Impatiens capensis		Balsaminaceae (Touch-me-not)
Solomon's seal, false	Smilacina racemosa		Liliaceae (Lily)
Twisted stalk	Streptopus lanceolatus		Liliaceae (Lily)
Stinking Benjamin	Trillium erectum		Liliaceae (Lily)
Trillium, large-flowered	Trillium grandiflorum		Liliaceae (Lily)
Bellwort, sessile-leaved	Uvularia sessilifolia		Liliaceae (Lily)
Bellwort, large flowered	Uvularia grandiflora		Liliaceae (Lily)
Crowfoot, small flower	Ranunculus abortivus		Ranunculaceae (Buttercup)
Violet, downy yellow	Viola pubescens		Violaceae (Violet)
Spikenard	Aralia racemosa		Araliaceae (Ginseng)
Mystery mint			Lamiaceae (Mint)

Ferns

Fern, christmas	Polystichum acrostichoides		Dryopteridaceae (Wood fern)
Oak-fern	Gymnocarpium dryopteris		Dryopteridaceae (Wood fern)
Wood fern, intermediate	Dryopteris intermedia		Dryopteridaceae (Wood fern)
Fern, sensitive	Onoclea sensibilis		Onocleaceae (Sensitive Fern)
Polypody, rock	Polypodium virginianum		Polypodiaceae (Polypody)

How hemlocks breathe

What: I used to describe the underside of a hemlock needle as being akin to an old classic longboard surfboard. It wasn't until a few years ago that I actually wondered what those little white lines on the underside of a hemlock needle actually were.

Ecological notes: Those two white lines are actually a bunch of little white dots, which are actually the stomata (the mouths, or sites of gas exchange, in leaves).

Because conifers weather out the winter with their needles still on the branches, they have to compete with harsh winter winds for water. They effectively have a water input of zero. With the ground frozen, the tree can't replace any of the water it might lose to transpiration (basically evaporation of water out of any openings in a leaf). Transpiration increases with wind that would carry water vapor away (much like how you can tell wind direction by licking your finger and holding it up; it feels cool on the windy side because the water is evaporating even though it's well below the boiling temperature where you'd expect it to go from a liquid to a gass).

Hemlocks would risk desiccation (severe drying) in the leaves unless it could somehow protect itself from the ways it loses water. It does this in a couple of ways. First, it has a super waxy cuticle. The waxy cuticle prevents transpiration from occurring on the top side of the leaf. Second, it protects the stomata (those openings) from being exposed to the wind by putting them on the underside of the leaf and having them in grooves.

Hemlock, the patient one

What: Even with the leaves off the trees and sounds (particularly I-89) filtering through the woods with reckless abandon, there's still a peacefulness to the movements of the woods in winter. While walking across the Winooski Bridge I admired the slow undulating flaps of a Cooper's hawk above and the odd oscillations of the water bubbling back and forth off the ice as it came to a halt in front of the dam. The hawk flitted gracefully to the west, cut a quiet line through dense air and alighted on a distant smoke stack.

There's an equal grace and peacefulness to the slow bending of a hemlock - what I call the Winter Tree - under the sway of the wind. Among the conifers, hemlock stands out to me as such a delicate and deeply cold tree. The rich green of the foliage feels more like the shadow of a leaf, like the tree was born in winter only to endure summer each year.

The branch above is about 2 3/4" across

Enduring the summer means slooooow growth. I was out harvesting wood for coasters, and I found a giant old hemlock that had come down across Wool Pullery Brook in South Burlington. I cut the branch from the trees in the photos at the top (about 35' from the trunk) right at the base where it came off of the tree (if the tree were still standing the branch would have been about 25' up). Hemlocks are about the most shade tolerant species, and a single hemlock needle can live for up to 40 years (in part because it can deal with as little as 10% light and still photosynthesize enough for the plant to keep it around; for contrast, white pines are far less tolerant of shade and lose about half their needles each year).

I guess I shouldn't have been, but I was surprised at how ancient the branch was given its size. It was too hard to count the rings by eye so I sanded and finished the "cookie", photographed it, then ramped up the contrast. Each arrow represents 10 years of growth. The rings were extremely tight, and there's a distinct boundary between the heartwood and sapwood (sapwood is the lighter section of rings on the outside). The branch was much less resinous farther out, indicating that the distinction was largely due to the tree needing extra support in holding up that branch for 106 years.

Where: Hemlocks grow at extremes - there are hemlock swamps and there are steep rocky hemlock slopes. It can grow in the shadiest of places, less than about 10% light. This tree was growing along Wool Pullery Brook in Centennial Woods.