Thursday, November 15, 2012

Marcescence in beech trees

Kaleigh Wood is a senior Environmental Studies in the Rubenstein School at UVM. She enjoys exploring outside, running and cooking.

A couple of weeks ago I was on a stroll through Centennial Woods (CW) for a class assignment. The leaves littered the ground with their colors and gave my steps a pleasant crunchy sound as I made my way deeper into the woods. I looked up to find that most of the trees had shed their leaves. I kept walking and suddenly I was surrounded by this beautiful tree that was still full of its vibrant orange leaves. While I haven't taken dendrology and my tree identification skills are sub-par, I did know this one. The tree that was still holding onto its exciting leaves was an American Beech (Fagus grandifolia). I started to wonder, why do Beech trees hold onto their leaves after all the other deciduous trees let theirs fall?

I went on a run with my trusty running buddy, Lily Morgan, who happens to have a strong passion for trees. I was explaining what I had seen in CW and started to ask her what she knew about the American beech; she started rambling some things in Latin and I quickly stopped her and asked her about the leaves and why they stayed on for so long. She gave me a lesson from Reading the Forested Landscape by Tom Wessels on beech. We found out that beech and oak trees are actually somewhere in between evergreen and deciduous trees, explaining why those tree species can hang on to their leaves throughout  the winter.

We wanted to know more, we found out the genetic reasoning why Beech can hang on to their leaves, but what was the ecological advantage of it? I explored the internet and found an article in Northern Woodlands magazine. The author, Michael Snyder, (who is the Chittenden County Forester in Vermont) explained that some plants will retain dead plant matter, known as marcescence. It turns out there are many theories to the advantages of marcescence. One theory is it’s an adaptive advantage for trees growing in dry and infertile areas (where Beech trees grow!), because if they do not drop their leaves onto the ground they deprive the soil of organic matter which other trees need. Beech and oaks don't need the added nutrients so they  continue to thrive. Keeping leaves on their branches and not on the ground allows them to out-compete other species surrounding them. Additionally oak leaves are high in tannins and reluctant to decompose, further reducing available nutrients to other would-be competitors.

Other advantages of marcescence are, trapping snow which leads to more moisture at the base of the tree, the dead leaves on the limbs protect buds from frost in the winter, and finally the leaves can protect the trees from browsers such as deer and moose. The dead leaves can hide buds so they are less likely to be eaten and are more likely to grow new buds and twigs in the spring. Not only do Beech trees provide CW with great views after most trees have dropped their leaves, but there are also advantages to this interesting adaptation.

No comments:

Post a Comment