Hemlock Tree
Matt Shapiro


(5) (Shwetha)

Canadian-Hemlock.jpg(9) (JLev)
Cone from Hemlock tree


Classification/Diagnostic Characteristics

Kingdom: Plantae
Subkingdom: Tracheobionta
Superdivision: Spermatophyta
Division: Coniferophyta
Class: Pinopsida
Order: Pinales
Family Pinaceae
Genus: Tsuga Carriere
(4) (JLau)

Known in Japan as the Tsuga, a hemlock tree is a cone bearing conifer tree with roots, a barky trunk and small thin coniferous leaves. They are pretty big trees, ranging from about 10 to 60 meters tall with grey or brown bark and short spur shoots. It gets its name from the scent that arises from the crushed leaves which resemble the smell of the unrelated plant poison, hemlock. (5)(Shwetha)

Hemlock trees include around eight to ten species that are distinguished by both cone and foliage characteristics. The mountain hemlock species T. mertensiani is under debate about whether it should be considered a hemlock tree because the cones are the longest in the genus and they are cylindrical rather than ovoid. The leaves are also less flattened and contain stomata above and below. (7) (JF)

Hemlocks have needles that have two white “racing stripes” on their undersides, and bark that is narrow, has rounded ridges, and thick scales. Its bark is usually within the spectrum of red to gray. It’s branches are thinner than spruce, fir, or pine, and therefore look “lacier” in appearance (8) (E.S.S.).


Relationship to Humans
However, Hemlocks are often not used as Christmas trees as they lose their needles soon after death. Although they are spared the chore of yuletide decorating, Hemlocks are used for a variety of different purposes. The wood is often used to make pulp and railroad ties. They are also used to extract tannin, an oil important in tanning leather. Some cultures even enjoy making tea from Hemlock leaves. (6) (SJ)

In the lumber industry, the Western Hemlock is an important tree. It is used to make paneling, flooring, and furniture. Although the Western Hemlock is used, many hemlocks are brittle when dry and difficult to work with. Landscaping industries also use hemlocks. They use them not only for decorative purposes but also for the prevention of stream bank erosion. (13) (WSS)
Habitat & Niche
Hemlock trees and other conifers are found in colder and dryer boreal or seasonal forests. The northern hemisphere is covered with such forests, especially in the cooler more northern regions.
It prefers acidic soils with moist, cool valleys that contain rocks. It can be found from Nova Scotia to Quebec to as far south as Georgia and as far west as Michigan. (6)(BB-V)
Hemlocks grow along either coastal sides from sea to mid elevation level and west of the Rocky Mountains. (19) (TM)

The green area indicates the range of native hemlock growth in northeastern U.S.
The green area indicates the range of native hemlock growth in northeastern U.S.
(16) (BH)

Predator Avoidance
The hemlock tree, being a plant cannot move, but there are few predators that prey on the hemlock tree. The hemlock tree’s worst enemies are the diseases that it can contract. To avoid these, the hemlock tree as well as all trees have a coat of bark over their trunk. The bark is typically darker than the tree’s interior and is quite tough depending on the tree
There are multiple hemlock tree diseases and pests . Root Rot attacks the roots of mountain and western hemlocks by sprouting button-shaped conks,a fibrous but sometimes fleshy fruiting body of a wood-rotting fungus that has a definite form and structure. Dwarf Mistletoe attacks western hemlocks with parasitic green shoots that steal nutrients from infected trees. Trunk Rot produces conks that severely decay western and mountain hemlocks. Woolly Adelgid is an insect that takes sapp from the base of canadian and eastern hemlocks needles and is the only one of these infections that insecticides has worked on.(11, SM)
Nutrient Acquisition
The hemlock tree obtains the majority of its nutrients through its root system. Roots are used to absorb water as well as minerals from the ground. The branching nature of roots gives it a high surface area to volume ratio allowing for maximum absorption. Minerals collected are transported through the xylem, tissue made of dead cells that transport minerals to all parts of a plant. In gymnosperms such as the hemlock tree, the xylem contains only tracheids, spindle shaped cells through which water and minerals are transported. Angiosperms and other plants also have vessel elements which gymnosperms lack.
Hemlock trees make their own food, like many plants. They do this by the process of photosynthesis, done within cell organs of plant cells called chloroplasts, which take the carbon dioxide (from stomata, special holes in plant) and water (from roots) and a series of complex chemical reactions undergo inside, ending in the production of glucose from these reactants. Glucose then enters the mitochondria of the cells to be used in metabolism. (1)(KG)

Reproduction and Life Cycle
The hemlock tree is a conifer, or cone bearer. It produces both male and female cones. The female cones are large and woody and are called megastrobili because they are much larger than the male microstrobili, which are herbaceous instead of woody. Wind carries the pollen to the megastrobilus. The pollen needs water to help it flow through small holes in the megastrobilus to the ovule where the pollen fertilizes the egg and creates a zygote. As the fertilized megastrobilus matures is begins to scale and the fertalized seed with an attached wing is revealed. The wind usually catches the winged seed and carries it from its parent tree.

Growth and Development
The hemlock tree starts as a small seed that germinates and eventually sprouts. When it is very young it seems herbaceous, but as it grows it develops its woodiness. Once mature enough it produces male and female cones for it to reproduce

Found most commonly in mountainous regions, the hemlock tree can grow to a height greater than 100 feet. It is a slow-growing, but long-lived tree whose optimal conditions are in the shade. It starts as an understory tree, a tree that grows well under larger trees, and pushes its way through the broad-leafed trees until it reaches fall sun. The tree can take anywhere from 250 years to 300 years to fully mature and can live for 800 years or longer. Identified as an evergreen tree, the hemlock has flat needles that are 1/3-2/3 inch long and about 1/2 inch long cones that mature during the year between September and October. The needles are short and soft unlike the pointy needles of similar firs and spruces. (3) (PS)

The hemlock tree is covered with woody bark as well as small linear scaly and flat leaves on its branches.

The hemlock's bark is it's natural defense from environmental threats. The bark also absorbs wastes into the dead cells and resin of which it is made up of. The bark consists of two parts: the secondary phloem, which transports vital molecules such as carbohydrates between the roots and the leaves, and the periderm (cork), which in itself consists of three layers of cells. The outermost layer of the periderm is completely dead because the inner layers cut off the outer ones from access to water. The patterns found in bark are caused by the trees growth: when the tree gets bigger the dead cells on the outside stretch and cracks form between them, creating bark texture. (12) (AA)

The most a hemlock tree will move is as a seed. The seeds have wings for the wind to catch so it can germinate and grow far from its parent tree. Human children enjoy picking up these seeds, throwing them up in the air and watching as the fall in a spiral fashion. Once the seed germinates and begins to grow it stays in the same place, but grows upwards and often in the direction of the sun.

Sensing The Environment
The hemlock tree, like most plants, utilizes phototropism to sense is enviroment. Simply put, phototropism is a why a plant grows toward the sunlight. It is a directional growth in response to a light stimulus. It is a bit unclear how it works to scientists. However, there is a little or two known about it. The plant will produce hormones called auxins which gather on the sides of the plant that are undergoing a definite decreased amount of photosynthesis than other area. Auxin will cause the sections to grow heavier, bending the plant the opposite direction, and into the sun. (AC = AWC) [1]

Gas Exchange
The hemlock tree requires CO2 to photosynthesize. It exchanges its O2 (byproduct of photosynthesis) with CO2 from the environment through stomata, small pores, in its leaves.

Stomata are open and close based on the water concentration of the cells around it. The plant cannot gain CO2 without losing water vapor. Because of this the plants open and close their stoma based on conditions of the environment including light, humidty, and temperature. (18)(BS)

Waste Removal
The hemlock tree uses its xylem, to remove waste from its cells.

Comprising the youngest layers of wood, the xylem (sapwood) is a network of thick-walled cells that bring water and nutrients from the roots through the tubes within the tree and to leaves and other parts of the tree. As the tree ages, the xylem beings to become inactive and die. (14) (MC)

xylem and phloem.jpeg(Shwetha)(17)

Environmental Physiology
Because hemlock trees often form dense, canopied forests, the forest floor of hemlock forests are usually very dim and shaded. Thus, hemlock trees have evolved to be incredible shade-resistant. While certain young hemlock trees may not receive enough light to grow significantly, they are still capable of surviving. In fact, many hemlock trees in Pennsylvania was found to be over 200 years old but only 2-3 inches in diameter. This shade tolerance ensures that hemlock trees grow to occupy the canopy if a dominant tree falls.[2] (FZ)

Internal Circulation
The hemlock tree has vascular system made of xylem and phloem. Xylem is used to transport water, nutrients, and waste though the tree. The system Xylem begins at the roots and extends through all parts of the tree. Phloem unlike xylem is living tissue. Phloem is used to transport sugar from where it is produced to wear the sugar will be needed or stared such as developing roots and parts of the tree
Chemical Control

Review Questions
1) What process does the Hemlock Tree use to reproduce? (LC)
2) How do hemlock trees acquire food and water? (DM)
3) Identify and explain the layers and composition of the Hemlocks bark. (DA)
4) How does the Hemlock tree use phototropism and why? (ES)


1. Hillis, David M., David Sadava, H. C. Heller, and Mary V. Price. Principles of Life High School Edition. Sudnerland, MA: Sinauer Associates, 2012. Print.
2. Adams, Douglas. "Chapter 1." The Hitchhiker's Guide to the Galaxy. New York: Ballantine, 1995. 1-5. Print.

3. http://www.dcnr.state.pa.us/forestry/hemlock.aspx
4. http://plants.usda.gov/java/profile?symbol=tsca
5. http://www3.amherst.edu/~ccsp01/HemlockAdelgid.html
6. http://www.yale.edu/fes505b/ehemlock.html
7. http://www.conifers.org/pi/Tsuga.php
8. "Quick Key to Identifying Hemlock." Hemlock ID. Maine Forest Service, 2005. Web. 13 Dec. 2012. <http://www.maine.gov/doc/mfs/hemlockID.htm>.
9. http://www.stilesnursery.com/photos/Canadian-Hemlock.htm
12. http://www.slideshare.net/halilcakan/bark-and-wood-anatomy-of-trees-presentation#btnPrevious
13. http://www.gardenguides.com/115414-hemlock-tree.html\
14. http://www.ncforestry.org/WEBPAGES/CLASSROOM%20ACTIVITIES/Trees/PartsOfTree/parts.htm


16. http://www.nyis.info/user_uploads/images/hwa2011.JPG
18. http://www.eoearth.org/article/Stomata?topic=49510
  1. ^ http://en.wikipedia.org/wiki/Phototropism
  2. ^