Common Name: Eastern Hemlock, Canada hemlock, Hemlock spruce – Hemlock is the name for the hop plant in both the Germanic (homele) and Finno-Ugric (humala) language groups. The hop plant is the source of “hops” used for centuries across much of northern Europe to impart a bitter flavor to liquors made from malted grain. The small flowers of the hop plant are similar to the flowers of the poison hemlock (Conium maculatum) which shares the same etymology and from which the hemlock tree gets its name (by indirect association). In other words, the poison hemlock looks like and was named for the hop plant and the hemlock tree shares a number of attributes with poison hemlock. The Carolina hemlock is very similar and difficult to distinguish from its collocated cousin.
Scientific Name: Tsuga canadensis – The generic name is from the Japanese word for the larch tree which, like the hemlock, is a member of the pine family. Most of the other trees in the genus Tsuga are indigenous to east Asia, primarily Japan. The species name is reference to the first classification of the tree in the Linnaean taxonomic system based on a specimen first sighted and identified in Canada. The Carolina hemlock is Tsuga caroliniana first distinguished in the Appalachian uplands further south.
Potpourri: Hemlocks are members of the ubiquitous Pinaceae or pine family which consists of conifer or cone-bearing trees that grow throughout the temperate regions of both the Northern and Southern Hemispheres and in mountainous tropical regions. The Pine family includes pines (Pinus), spruce (Picea), firs (Abies), hemlocks (Tsuga), larches (Larix), and Douglas-firs (Pseudotsuga or false hemlock). [1] Since they are large trees that grow in dense clusters, they are among the most important trees of the timber industry, providing 75 percent of all lumber, and 90 percent of paper pulp. There are over 200 species worldwide of which about 60 are indigenous to North America. Pine family trees are self-pollinating, or monoecious, contributing to their evolutionary success at the expense of genetic diversity. The “naked seeds” that literally define the Gymnosperms (gymno is Greek―gymnasiums were places for naked exercise) are at the base of the female pinecone scales fertilized by male cone pollen wind-blown from the same tree. The pollen that is deposited on the megasporangium of the female cone in the spring ceases growth through the winter, consummating fertilization the following year. [2] In good time, you get a pine.
Hemlocks can most easily be distinguished by their needles, a term referring to the narrow, pointed leaves that, except for the larch, do not fall off over winter giving rise to the more general term evergreen. Hemlocks needles are short, arrayed in two neat rows, one of nature’s better options for higher mountains and boreal forests. However, needles do have a lifespan. Pine trees lose about one fourth of their needles every year resulting in trails coated with a soft cushion of decaying needles that suppresses almost all other plant growth, one of the best treads for foot travel. The “evergreen” needle as a leaf form is an evolutionary result of several factors involving both latitude and geology. The primary determinant is the length of the growing season, which can vary from as short as 65 days in New England to an average of 250 days in the southeast. All things being equal, a plant will trend toward greater leaf area exposed to as much sunlight as possible. Photosynthesis in the chloroplast cells of the leaves converts sun photon energy to the hydrocarbon molecules of biology. Broadleaf trees grow where they can, and evergreen needle trees grow where they can’t.
When the non-growth colder season approaches, broadleaf trees are better off wintering over with bare branches, having adequate time to replenish their foliage the following spring. In northern latitudes, there is simply not enough time to restock the canopy with sun gatherers, so they persist year-round as narrow needle-like leaves. Temperature is a second factor due primarily to physics; when the freezing point is reached, the uptake of water is squelched and growth is curtailed. Since average temperature drops about 3 degrees F every 1,000 feet, mountainous terrain has the same effect as latitude on the growing season so evergreens also prevail in higher elevations. Needle trees are also favored in northern latitudes and uplands because they are winterized with wax-coated needles and resin-infused wood and roots. The conical shape of many conifer trees with their one dimensional needles are also better at survival in heavy snowpack. It should be noted that the pine barrens of New Jersey and the wide expanses of scrub pines across the south are neither mountainous nor northern. Some species of pine thrive in dry sandy soils where periodic wildfires have historically been the norm. Their cones are serotinous, which means that they evolved to burst open after a fire to spread the seeds of restoration, eventually becoming the dominant species. [3]
That hemlock trees have the same name as the poisonous hemlock plant cannot be a matter of chance etymology. They have some things in common, but not the notorious toxins of the latter. The “drinking of the hemlock” was the standard method of execution in Ancient Greece. One of history’s most enduring dramas is the trial of Socrates by the popular court or dikasterion comprised of 500 Athenian citizens in 399 BCE. He was prosecuted for undermining religious faith in the “gods that the state recognizes” by introducing new “demonical beings” and for “corrupting the youth” and found guilty by a slight majority. The hemlock execution of Socrates is considered by many historians to mark the end of the Golden Age of Greece. [4] Poison hemlock was thus well known throughout Europe by the Middle Ages both for its toxicity, and, in small doses, for treatment of a variety of ailments. There is evidence of its use for the treatment of cancer, as a narcotic or analgesic, and even as an anti-aphrodisiac (perhaps by killing the object of desire). [5] Because of this, many Europeans were familiar with its shape when growing and its smell when ground into powder. However, since there were no hemlock trees in Europe, it took the discovery and exploration of the Americas to associate the poison hemlock plant with its namesake tree.
The hemlocks of North America were almost certainly first sighted along riparian riverbanks by French explorers who penetrated the mainland by sailing up the St. Lawrence from the North Atlantic in the 16th century. Their knowledge of the smell and branching pattern of the poison hemlock led to applying the familiar name to the unfamiliar evergreen tree due to its similar characteristics. This is corroborated by the British Cyclopedia of 1836 in noting that the hemlock tree was “so called from its branches in tenuity and position resembling the foliage of the common hemlock.” Conium, the genus of the poison hemlock, was purposely chosen because the plant looked like a miniature cone-bearing tree. In the New World, where there were so many new and strange plants, any means of distinguishing one species from another by using a mnemonic brought some order to the chaos. To differentiate the evergreen version of hemlock from its doppelgänger, the compound name “hemlock spruce” was applied. [6] Spruce trees of the genus Picea prevail in boreal forests across North America and Eurasia. Spruce is an anglicized version of “from Prussia” due to the prevalence of native spruce trees along the Baltic Sea near present day Lithuania. Prussia was the ancestral home of the medieval Teutonic Knights that grew in prestige and power, uniting the disparate Germanic states to form a unified Germany in the 19th century. The hemlock spruce is called Pruche du Canada in Quebec, further evidence of Prussian origin. It was later moved from the spruce to the pine family.
Eastern hemlock or hemlock spruce is the most shade tolerant of all tree species and can survive with as little as 5 percent full sunlight. Since the conversion of solar energy to produce hydrocarbon energy is the foundation of life, its lack can only be compensated for by slow growth. Like Treebeard, the ent of Tolkien’s mythical Fangorn Forest, hemlock growth is slow but inexorable. A one-inch diameter (usually reported as dbh―diameter at breast height―to account for irregularities) hemlock can be over 100 years old. Since hemlocks can grow to over six feet dbh with a height of over 150 feet, it follows that longevity is another characteristic trait. The record age for a hemlock is 988 years, older than Noah’s 969-year-old grandfather Methuselah, the epitome of lifetime endurance. Once established, a hemlock canopy blocks sunlight from penetrating to the understory, snuffing out most arboreal competition. The subsequent microclimate of dense shade with a deep duff layer retains moisture and sustains uniformly reduced ambient temperatures. Not surprisingly, the relatively exacting moisture and temperature requirements for hemlock germination are met by the conditions that they create. [7] But there is more to forest soil management than trees. There are also fungi.
Pine family trees like hemlock are connected through their root systems with fungi that surround them, an arrangement know as ectomycorrhizal, “outside fungus root” in Greek. About 90 percent of all plants form mutualistic partnerships with fungi to gain access to essential soil nutrients like phosphorus and nitrogen, with the plant providing up to ten percent of its hydrocarbon sugar output to root fungi in return. For most plants, the mycorrhizal relationship is an option that results in more robust growth. For trees of the Pine family like hemlock, the mycorrhizal relationship is universal. Many different species of fungi are involved with the roots of any given tree. While there have been no studies for hemlocks, the closely related Douglas firs (Pseudotsuga menziesii) are estimated to have over 2.000 different species of associated fungi. [8] The kingdom Fungi is not uniformly benign, however, as all living things must find their niche in the tangled web of life as a matter of survival. The subsurface soils kept moist by the hulking hemlocks are an ideal habitat for mold, another broad category of fungi. Seven species of fungi attack the seeds of hemlock resting on the moist soil awaiting the magic of germination. One mold species, Aureobasidum pullulans, was found growing on almost three fourths of all hemlock seeds, impeding their full function. Hemlocks, when they eventually keel over, provide yet another form of fungi, the saprophytes that feed on the dead. Were it not for the fungi that consume the cellulose and lignin from which tree trunks are made, the world would be covered with tree trunks and none of their carbon would be returned to the atmosphere. Because hemlocks are so pervasive, one species of fungus aptly named Ganoderma tsugae or hemlock polypore, subsists exclusively on its deadwood. Also called varnish shelf, it is one of the most recognizable of all fungi and is closely related to one of the most important fungi in Asian medicine (see full article for further details).
The hemlock is listed on the International Union for Conservation of Nature Red List as near threatened. [9] This surprising state of affairs is not the result of clear cutting and overharvesting, although human impact has surely had deleterious effects. The high point of hemlock harvest was at the turn of the last century when the wood was used primarily for home construction roofs and flooring. As the population surged in the decades that followed and newspapers of the golden age of Hearst and Pulitzer proliferated, hemlocks became one of the primary sources for paper pulp. The effects are exemplified by Michigan’s growing stock decreasing by over 70 percent between 1935 and 1955, a result of the slow growth of hemlock relative to its removal. However, the real culprit that threatens hemlocks is a sap sucking insect closely related to aphids, the bane of gardeners and food for ladybugs. The woolly adelgid was probably introduced from Japan in the early 1950s somewhere in New England and has now spread to 19 states and two Canadian provinces.[10] The larvae of the adelgid suck the body fluids from hemlock needles at their base, covering themselves with a fluffy white layer (hence woolly) to protect against predation (see full article for further details). A death by a literal thousand cuts ensues that can take decades but is in most cases inevitable. The hemlocks of Limberlost were the only old growth tract in Shenandoah National Park. They had been so weakened by woolly adelgids that they toppled during hurricane Fran in 1996. The hemlocks are just starting to recover almost thirty years later (note fallen hemlock trunk in foreground in photo).
Unlike its poisonous namesake, hemlock is not only edible but salubrious. It has been attested that the entire Pine family “comprises one of the most vital groups of edibles in the world.” [11] This would mostly apply to northern latitudes where the paucity of winter food could result in starvation absent the resort to eating pine tree inner bark, a thin layer called the cambium. The nutritious cambium is responsible for the formation of the water transport xylem on the inside and the hydrocarbon food transport phloem on the outside; in other words, it makes the tree trunk. For soft wood pine trees stripping off the outer bark layer to gain access to the cambium can be readily accomplished with primitive scraping tools. The native peoples of North America collected cambium which was cut into strips eaten either raw, cooked, or dried and ground into flour to make bread, a practice adopted by early colonists. The Adirondack Mountains of New York derive from the Mohawk word haterỏntaks, which means “they eat trees.” The healthful benefits of hemlocks and other pines are further enhanced by high concentrations of anti-inflammatory tannins and anti-oxidant ascorbic acid/vitamin C in all parts of the tree. The various Indian tribes had diverse uses, extending from pine tea tea to treat colds to thick pinesap paste applied to wounds as poultice.[12] One early colonist wrote in his diary in the mid 19th century that “I never caught a cold yet. I recommend, from experience, a hemlock-bed, and hemlock-tea, with a dash of whiskey in it merely to assist the flavor, as the best preventive.” [13]
References:
1. Little, E. The Audubon Field Guide to North American Trees, Eastern Region, Alfred A. Knopf, 1980, pp 276-301.
2. Wilson, C. and Loomis, W. Botany, Holt, Rinehart and Winston, New York,1967, pp 549-570
3. Kricher, J. and Morrison, G. A Field Guide to Eastern Forests of North America, Peterson Field Guide Series, Houghton Mifflin Company, Boston. 1988, pp 9-10.
4. Durant, W. The Life of Greece, Simon and Schuster, New York, 1966, pp 452-456.
5. Foster, S. and Duke, J. Medicinal Plants and Herbs of Eastern and Central North America. Peterson Field Guide Series. Houghton Mifflin Company, Boston, 2000, pp 68-69.
6. Earle, C. Tsuga, The Gymnosperm Database, 2018, at https://www.conifers.org/pi/Tsuga.php
7. Godman, T. and Lancaster, K. “Pinaceae, Pine Family” U.S. Forest Service Report at https://www.srs.fs.usda.gov/pubs/misc/ag_654/volume_1/tsuga/canadensis.htm
8. Kendrick, B. The Fifth Kingdom, Focus Publishing, Newburyport, Massachusetts, 2000. Pp 257-278.
9. https://www.iucnredlist.org/species/42431/2979676
10. https://explorer.natureserve.org/Taxon/ELEMENT_GLOBAL.2.131718/Tsuga_canadensis
11. Angier, B. and Foster, K. Edible Wild Plants, Stackpole Books, Mechanicsburg, Pennsylvania, 2008, pp 168-169.
12.Ethnobotany Data Base at http://naeb.brit.org/uses/search/?string=tsuga+canadensis
13. Harris, M. Botanica, North America, Harper Collins, New York, 2003, pp 44-46.
Hiker's Notebook 