Leaves are out along the Pacific Coast! Thanks to schools in Washington and British Columbia for sending this news. What about the trees where you live? Please let us know when your leaves are the size of a U.S. quarter. Simply send an e-mail message to: jn-report@learner.org
Have you noticed that spring comes earlier to British Columbia than in places like New York and Michigan, which are not as far north? Robins returned there sooner, tulips are blooming already and the leaves are out. How would you explain this?
Challenge Question # 71
"Why do you think spring arrives in British Columbia before it reaches Michigan?"
To respond to this Challenge Question please follow the instructions at the end of this report.
In our last report we ask, "How do trees 'tell time'?" Here are ideas from 4th grade students in Bar Harbor, Maine:
From MAINE:
"I think trees tell time by the heat of the weather and how much water
they get. Then the leaves start to grow."
Alan Simons
"I think trees tell time by how long the days are and sunlight they
get."
Tristan Birkenmeier
Grade 4, Conners School, Bar Harbor,ME
Ms. Hersey mhg4@emerson.u98.k12.me.us
How would a climatologist answer this Challenge Question?
Here are some interesting comments from Dr. Mark Seeley, Professor and Extension Climatologist at the University of Minnesota:
"Trees respond perhaps most to daylength in terms of budding and leafing out in the spring, and in changing color and dropping leaves in the fall. Bear in mind that when trees go through the most rapid changes in life cycle in spring and fall, daylengths are typically changing on the order of 3 to 4 minutes per day, which adds up pretty quickly.
"But in addition to daylength being a trigger, temperature modifies this response. Temperature can either accelerate or inhibit these processes to some extent.
"Some tree phenology, such as crab apple blossoming, has been related to the accumulation of degree days above a base of 40 degrees F. May budding, blossoming and leafing out events occur between 300 and 500 degree days each spring."
We then asked Dr. Seeley, "If if gets unseasonably warm during winter, does the temperature ever "trick" the trees into producing leaves early?"
Dr. Seeley responded, "Yes, to some extent. If the ground is thawed and daylength is rapidly increasing (such as March and early April), physiological activities can be accelerated by temperature. Roots may start to take in moisture, cell division may occur at growing points (crowns and buds) and previously hardened plants cells may rehydrate. But once this happens trees may be more suceptible to sudden cold snaps.
And finally we asked, "What happens to trees and their leaves if a hard freeze occurs after the leaves are already out?"
Dr. Seeley said, "This can happen! In the spring of 1992 in Minnesota, frost occurred in the last week of May and even on the Summer Solstice (June 20) that year. Some plants and trees had to use their food reserves to releaf that year. This put added stress on them. This is unusual in Minnesota and happens perhaps only once every 20 years or more."
Leaf -Out Observations Through March 25, 1996
From WASHINGTON:
March 17, 1996
I have a small Ginkgo tree that I have had for three years that I
keep outside on my porch. Last weekend, it had its first green buds.
You probably don't get too many reports about these living fossils.
They do lose their leaves each winter.
Wesley Harness, Grass Lake Elementary
Kent, Washington
wharness@kent.wednet. edu
From BRITISH COLUMBIA:
March 22, 1996
It has been warm for the last week and all the leaves came out.
Joel Roberts & Lisa Young
Cross Roads
Victoria, B.C
lyoung@pinc.com
From WASHINGTON:
March 25, 1996
The leaf is the size of a quarter on a black cottonwood tree.
Sam Pitt & Sharon Burke
Benjamin Franklin
Kirkland, Washington
sburke@orac.lkwash.wednet.edu
How to Respond to Challenge Question # 71
1. Send an e-mail message to jn-challenge@learner.org
2. In the Subject line write: Challenge Question # 71
3. In the Body of the message, answer this question:
"Why do you think spring arrives in British Columbia before it reaches Michigan?"
The Next Leaf-out Report Will be Posted on April 19, 1996
 |
|
|---|
