Why Do Some Leaves Persist On Beech and Oak Trees Well Into Winter?
Photo by Blake Gardner
Those dead, bleached-brown beech and oak leaves rattling in a January wind – but somehow still clinging to their twigs – are symbolic. Like ecological pennants, they announce that beech and oak are not quite finished; that these species are still works in progress.
To understand this, consider both the physiology and the evolutionary history of trees. All living trees shed their leaves at some time. Every leaf has a finite life span; each will fade and fall at some regular interval. But there is great variation in the timing of this leaf fall. At one end of the spectrum, there are evergreens. Though they appear to be fully leafed at all times, evergreen leaves are not always green, and entire age classes of needles die, turn brown, and fall every year. On the other end of the spectrum are deciduous trees, which seem to drop their leaves all at once after a pigment party every fall.
For a very long time, evergreen was the only way to be. Literally. Evergreens were the first trees on the planet. Populations of those earliest evergreen trees encountered changing growing conditions as they expanded their ranges and as the long march of time proceeded. As if to hedge their bets against future change, trees began to develop different ways of doing what trees do, including new ways of growing and shedding their leaves. Thus our colorfully famous, broad-leafed hardwood was born.
Today in our woods, we still have several evergreens, like pine, spruce, hemlock, and fir. And we’ve also got the relative newcomers with short-lived leaves – birch, maple, cherry, and aspen, for example. But then we have a third class of tree in beech and oak that seems to represent a middle ground of sorts between evergreen and deciduous. Their leaves die, but many don’t fall when they die. Botanists call this retention of dead plant matter marcescence.
Evergreen-ness is thought to confer an advantage to a tree by increasing the time available for its leaves to remain photosynthetic and by reducing nutrient losses associated with dropped leaves. Deciduous leaf fall, on the other hand, is considered an adaptation that evolved to allow trees in seasonally changing environments to reduce water loss and frost damage during unfavorable seasons while increasing their photosynthetic efficiency during favorable seasons. These are two strikingly different approaches. Each has its advantages and downsides, and over millennia, most species seem to have settled in to being one or the other.
The question remains then as to whether there is any ecological advantage to being somewhere in between. While physiologists agree that marcescence is a juvenile trait, most commonly observed on young trees and on lower branches, there is considerable debate about why some species would seem to be deciduous in all other respects except that they delay the physiological process of leaf shedding.
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.
We do not know whether marcescence provides a competitive benefit to beech and oak, but we do know that these two species are closely related; they are in the same family (beech). In fact, the beech family includes many, get this, evergreen species (live oaks and tanoaks, for example, which do not grow in our region). Marcescence may indeed be helpful to trees living in dry, cold, deer-infested environments. But it may also be simply a sign that beech and oak are evolutionarily delayed, still on their way to becoming fully deciduous from their more evergreen past.
Michael Snyder is the Chittenden (Vermont) County Forester.
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Discussion
Great article! I have a theory that Oak trees retain their leaves to protect the acorns as they develop. I have not documented it, but I have noticed in years when ther red oaks retain their leaves well in to January and February, they have a good crop the following year. I have not noticed this in white Oaks. I am not sure if this theory also pertains to the Beech trees, but I will be watching next year, because this year they seem very persistent in their leaf retention.
Tom Farrell in Connecticut | Jan 11, 2011
As a somewhat avid walker/hiker, I have always wondered why the leaves did cling to some trees longer. On a recent hike with a state forest ranger and a naturalist, they pointed out the mighty oak, and the beech trees and brought this to the groups attention. No one had a clear answer. So your article had made some sense to this mystery. I will be using your ideals as my new found knowledge on future hikes.
I enjoy reading your articles, and enjoy all the facts and especially the pictures and “What in the woods is that.” By far, my best reading. Thank you from a fellow woodsman down in Tennessee.
Bill Davis in Mt Juliet, Tennessee | Feb 11, 2011
I have a tree in my garden which I have always taken to be a white oak. Being from Windhoek in Namibia this is a highly unusual tree for our environment, indeed I am not actually aware of any other in Windhoek at all. Over the last few years it has been very noticeable that, although all the leaves turn brown in autumn (May/June here being in the southern hemisphere fewer and fewer are actually shed. With new growth in spring the old brown leaves stay on the tree and appear to interfere with new growth. Apart from being unaesthetic these areas of dead leaves harbor pests such as aphids and scale insects which afflict the tree during summer. Each year this has become worse. The winters here are generally mild with few nights of frost whilst the peak summer temperatures are up to 40 centigrade. Rainfall is also primarily late summer with little or no precipitation in the winter, certainly no snow. Last year I manually removed the dead leaves in late winter, which took some effort, but which the tree seemed to appreciate based on the strength of the new growth. I’d be interested to know whether the failure to shed the old leaves when the new leaves grow is a problem or just part of a natural process? Might it perhaps be caused by our climate? I have inquired from local nurseries but have not received any helpful comment due, I think, to the general rarity of the tree here.
Peter Forster in Windhoek, Namibia | Jun 15, 2011
Nice article. One speculation: Could those clinging brown leaves create a little extra shade, thereby discouraging competing evergreens under the canopy of the young oaks and beeches? That would be particularly important in soils that don’t allow for as rapid growth of the oak/beech.
Chris Fanger in Massachusetts | Jan 23, 2012
IS there a way to strip the dead leaves from oaks?
Frank | Sep 28, 2012
Frank,
We here at Northern Woodlands are unfamiliar with any particular method for stripping dead leaves from oaks, as none of us have ever tried to do that.
Meghan Oliver in Corinth, VT | Oct 03, 2012
Is there a chemical that will remove marescent leaves from a tree? some witch hazels retain their leaves and hide the flowers
Fred Averill in Charlottsville, va | Oct 14, 2012
We have 8 large, old oak trees…and have often wondered why their leaves just seem to hang around and hang around….except for the multi-billions on the ground that we rake into huge piles. I can use SOME as mulch, but most get sucked up by big city machine that then takes them to the landfill to be turned into topsoil. Your article and the various theories are quite interesting. A few oaks are native to the tallgrass prairies here…perhaps after a long cold winter the remaining leaves added nutrients to give the prairie grasses a boost?
A related topic: acorns. Many more than usual this fall. A Master Gardener suggested the trees felt stressed by the drought and produced more “babies” to ensure long-term survival. Any thoughts?
Marti Garrison in Northeast Iowa | Nov 01, 2012
There are many beech trees behind our house. Some drop their leaves in the fall & some hold on to some leaves until spring. They seem to be the same type. Wondering if some are male & some female. If so, what is the purpose & which kind holds on to the leaves?
Gail brown in Piedmont region of nc | Jan 14, 2013
Gail,
Beech trees have male and female flowers on the same tree, so that wouldn’t be a reason. Typically, among trees that hang onto leaves after they’ve turned brown, it’s the younger ones that do this the most. You don’t often see leaves in winter way high up in a big beech tree. My guess is that it’s the usual small genetic variability that explains this. Beech and oak are believed to have originated in more southern climes and it’s been said that these species “have not yet perfected the deciduous habit.”
Ginny Barlow in Corinth, VT | Jan 16, 2013
You answered my question about beech leaf retention. Since you are really into trees, wondered if you know what a “Cork” pine is—actual species or type of White pine. I have one that I bought at a nursery in New Jersey—does not look like a white pine—bark definitely looks “corky”.
mitchel goldman in cheltenham, PA | Jan 21, 2013
Other than an axe or chainsaw, is there a forestry tool available that makes “ringing” or cutting the bark in a circle off a tree a little easier task to terminate undesirable species for forestry management purposes?
George
George Pruitt in Middle Tennessee | Feb 09, 2013
Girdling a tree, as George described in the above post, is a technique used to eliminate poor stock and undesirable trees without the involved work of felling. Girdling also allows smaller trees to have the support and shelter of the girdled tree while no longer having to compete with it for nutrients and sunlight. As the girdled tree decays, the smaller trees around it grow and take up the space once occupied by the girdled tree.
And George, I’m sorry to report that the tools for doing this work manually are indeed the axe and chainsaw. An axe can be effective on smaller trees especially in the spring when the bark is loose; for larger trees with tougher bark, a chainsaw is the right tool for the job.
Carl Demrow, Tricks of the Trade Columnist
Carl Demrow in East Orange, VT | Feb 12, 2013
Just curious, I was hiking in the woods one day and came across an ash tree with all its leaves still on it. The only thing strange about it was that the leaves were pure white. Is there an explanation for this or is it a phenomena, I have a picture of it. Kinda of gave me the creeps everything around it was dead. It was the end of March btw so those leaves have been there for quite some time and ive never seen leaves turn white. Any answers?
Jack in Northern New Jersey | Mar 27, 2013
I’ve lived here over 20 years and for a good part of that time have wondered about the young beeches keeping their leaves all winter. Today I noticed the leaves have shriveled markedly overnight, and are starting to fall. It looks like the new leaves are about to come out.
This article answered most of my questions, thanks.
I’m curious if the old leaves, though ‘dead’, could be directly supplying nutrients back to the budding branch, before falling off.
The change in the old leaves overnight was remarkable. I’ll start observing these things more closely each year to see if it happens this way every year. I’m also going to try to keep track of whether the leaf retention is due to the age of the tree or the height of the leaf, as higher branches are subject to more wind.
Dennis Farr in Clinton, TN | Apr 05, 2013
Thanks for answering a question I’ve been asking every winter as I admire the pinky beige leaves giving roadside woods color when otherwise pretty dull. Does anyone know how many years one can expect to enjoy the marcescence until the tree outgrows it? I would like to plant some to replace my dozens of Sandy victims and if I get them about six feet tall, could I hope for more than two or three years before they get too grown up for the look I admire?
Kathy in Westchester NY | Apr 13, 2013