White Oak Tree Marcescence In Northern Illinois - 2019

Here's a third in a series of posts in the garden diary that is showing off this year's foliar marcescence in our backyard for this Fall/Winter 2019.  First was a couple of photos of our Frans Fontaine Fastigiate Columnar Hornbeams (European, too.  But, that's far too many descriptors for one tree, right?).  Then just yesterday, I posted a photo of a Chanticleer Flowering Pear (Cleveland Pear) tree that was also retaining all of the leaves after most of the trees have dropped.

Today is a photo showing the two large Oak trees in our yard.  One on the southside (that lost a limb earlier this Fall) and one on the north in the foreground of the photo.  Oaks are well-known for retaining their leaves all Winter long and dropping them come Spring when the buds push off the dead leaves and they drop to the ground.  Northern Woodlands Magazine has a piece that talks about a couple of potential evolutionary reasons why these Oaks are keeping their leaves.  From that Northern Woodlands story (found via this U of I extension forum post):

Some ecologists suggest that marcescence has adaptive significance for trees growing on dry, infertile sites. Sure enough, that’s often where we see beech and oak growing well and outcompeting other species. The thinking is that retaining leaves until spring could be a means of slowing the decomposition of the leaves (they would rot faster if on the ground) and that dropping them in spring delivers organic material (think compost or mulch) at a time when it is most needed by the growing parent tree. Even small amounts at the right time could shift the competitive advantage toward these species on poor sites. 

Others suggest that retained leaves, particularly on young trees and the lower branches on bigger trees, is an effective means of trapping snow like a fence, leading to more moisture at the base of the trees come spring. Still others have hypothesized that persistent leaves might provide some frost protection for buds and new twigs over winter. And at least one study suggested that marcescent foliage could be a deterrent to browsing by deer and moose. Buds hidden by clusters of dead leaves do not get eaten and thus live to become new shoots and leaves in spring.