Friday, February 29, 2008

Looking for Spring? (and Today's Science Lesson)

I found this Canada goose wandering across the surface of an icy pond about 7:30 a.m. this morning as I was leaving the cabin for work. A second goose was near this one, and they both looked a little lost. Perhaps they were looking for open water. Perhaps they were eyeing potential nesting spots. They sure seemed to be looking for something that they hadn't found yet.

Today's science lesson is a report on what I found out about trees that hold their leaves through the winter. There's a name for it. It's called marcescent leaves. After agreeing on the name, scientists apparently don't agree on much else about it.

But I’m getting a little ahead of myself, so let’s back up a bit. Marcescence literally means "to wither without falling off," which is a good description of what I’m seeing with beech trees around the cabin right now. The leaves do fall off eventually, of course, but not until spring when new buds push them off.

The scientists agree that oaks, hornbeam and beech trees are the species most likely to exhibit marcescence. And they further agree that it’s the younger trees or sometimes the lower, younger branches of older trees that are most likely to have marcescent leaves.

Now for the muddy part. No one seems to agree on why it happens.

One scientist says that the trees get the benefit of some extra photosynthesis by holding onto their leaves, effectively extending their growing season a bit. Another says marcescence is actually disadvantage for the tree because insects love these dead leaves, and one study showed that trees with marcescence had higher numbers of galls or tumors than trees that didn’t have it.

Another study says marcescence is a benefit because it keeps deer and moose from eating the twigs because the attached leaves make the twigs less nutritious and tasty. Another scientist seems to have given up entirely and just said, "sometimes there doesn’t have to be a reason."

After hearing a different reason from as many different experts, I gave up. That's enough reasons for me. So here in a nutshell (so to speak) is the story about trees that hold their leaves throughout the winter. Please pick your own reason for why marcescence occurs. Once those leaves finally do fall, it's a pretty safe bet that spring won't be far behind.

4 comments:

Lynne said...

Wel, that was clear as mud. But at least we have a name for it!

Cathy said...

Thank you for looking that up, the oak in front of the house held on its leaves this year. Have to admit, looks pretty when there's a bit of snow on it and tonight, might get about 6 inches of snow. Where's spring!!

ChicagoLady said...

*waits for those beech leaves to fall*

PA-Birder said...

Here on the Big Spring which doesn't freeze over Geese are pairing up and claiming out a breeding territory. I don't know if you pair of Geese are trying to do the same but are just a little early. Thanks for the info about the large oak trees that dominate my yard. I notice some varieties hold their leaves more/longer than others.
Vern