The Long-Lived Eastern Hemlock |
It is easy to locate an evergreen in a sea of bare-branched trees. The dense green leaves are an easy tell, as is the straight trunk and tall height. But which evergreen is it? To identify an Eastern hemlock (Tsuga canadensis) you need to look at the needles. These are dark green, flat, 1/2in. long with a slightly pointed tip, and grow in two rows, with an extra row of flattened needles on top of stems, creating a spiral arrangement. The underside of each needle has 2 white stripes on either side of the midvein. This waxy white coating protects the stomata which are pores that allow for gas exchange and facilitate photosynthesis. Small, 3/4in. brown, oval shaped cones hang from the ends of branches. If the cones are open, they have already released tiny, winged seeds that form at the base of each scale. Finally, the entire tree has a pyramidal shape with widely spaced un-forked branches that are flexible, and bend easily in wind and snow. |
|
|
|
Like the American beeches, the Eastern hemlock is also under threat from an invasive pest. The woolly adelgid was first discovered in 1951 in Virginia, and has been spreading ever since, colonizing hemlock forests from Georgia to Maine and into southwestern Nova Scotia, as well as western Michigan. There have been numerous studies and attempts at controlling the adelgid, often using a combination of chemical, biological, genetic and pruning techniques. With so many scientists working on this problem, there is hope that the woolly adelgid can be controlled and hemlocks can rebound. |
|
|
|
Outdoor Journal Activities |
-
Step back to look at the whole tree. Sketch its architecture and note what is around it. Can you estimate its height? Measure the circumference of the trunk 4 feet above the ground. Touch the bark and note its color and pattern.
-
Examine the needle arrangement on stems and branches. Note how each needle is attached to the stem. Measure length of individual needles. Note any green color variation between needles on tips of branches and those further along the branch towards the trunk. Draw and record all your observations!
-
Turn needles over and observe using a magnifying glass. Look for two distinct white lines along the needle midrib. Those lines are stomatal bands, places where pores (stomata) used for gas exchange are found. Crush several needles to release scent chemicals. What does it smell like to you? What does it remind you of?
-
If you find cottony white bits at the base of needles along the branches, you have found evidence of the wooly adelgid insect. These are egg sacs and each sac laid by one individual contains 100–300 eggs! Do some mental math to estimate the level of infestation.
-
Look for small oval cones about 3/4in long found on the tips of the branches. Or look for cones on the ground under the tree. There are 2 winged seeds resting at the base of each scale. Carefully peel back the scales of closed mature cones to see if you can find them. Use a magnifying glass to help! When the seeds are mature and the weather is dry, the cones open to allow the seeds to disperse.
|
|
|
|
-
Simulate the damage done by the wooly adelgid to understand how serious this invasive pest is. This activity uses a straw, water, and a pushpin to represent a hemlock branch, the tree's nutrients (water), and the adelgid.
-
Start with a student sipping water through a straw to show a healthy tree taking up nutrients.
-
Have another student (the "adelgid") poke holes in the straw, which represent damage from the pest.
-
The "branch" will find it harder to sip the water with each new hole, demonstrating how the adelgid weakens the tree by damaging its vascular system, stealing sugars and eventually starving the tree.
-
Create a steam infusion for aromatherapy. Boil water and add crushed fresh hemlock needles (without any adelgids!) and thin twigs. Turn off heat, cover the pot and let steep for 15 minutes. Uncover and allow the forest like aroma fill the room. Experiment with different quantities of water, hemlock or steeping time to discover the best proportions of materials. Measure and record each trial and create an assessment tool to evaluate each trial in terms of smell, color or any other marker you choose.
|
|
|
|
Virtual Learning Adventures |
This winter, bring nature learning indoors with webcasts and on-line education resources from the Forest Service and Natural Inquirer. |
|
2026 Outstanding Science Trade Books |
A collection of the best non-fiction and biographies written for children, with many titles about the natural world! |
|
|
|
|
|
|
|
|
|
|
|
