Thursday, March 27, 2014

Marcesence - Photo essay

What: One of my students, Kaleigh Wood, posted about marcescence a couple of years ago. Marcescence, which is common in trees in the oak family, fagaceae (e.g. oaks and beeches), is the process in which the leaves die in the fall before the abscission layer completes the process of releasing the leaf from the tree. I think that these trees just have poor timing and cold weather kills the leave. Others suggest that the dead leaves help protect from the cold, water loss due to wind, or deer browse.

The cost of keeping leaves on is that harsh winter winds could rip the leaves off the tree, exposing the branch to insect predators and pathogens. I suppose another overlooked benefit could be that oak leaves are highly acidic and have high concentrations of tannins. There might be incentive not to drop leaves, where the acids and tannins would leach directly into the soil, making growing conditions for the tree more difficult. By retaining the leaves, the acids and tannins may break down before reaching the soil.

 Whatever the reason may be, the leaf petioles on this red oak (growing along the edge of an open field) had been shredded. Some leaves still barely clung to the branches, but mostly all that remained were the frayed fibers of the petioles.

No comments:

Post a Comment