What Is Marcescence: Reasons Leaves Don’t Fall From Trees


By: Tonya Barnett, (Author of FRESHCUTKY)

For many, the arrival of fall marks the end of the gardenseason and time to rest and relax. The cooler temperatures are a much welcomedrelief from the summer heat. During this time, plants also begin the process ofpreparing for the winter ahead. As the temperatures change, the leaves of many deciduous trees begin to show bright and vibrant colors. From yellow tored, fall foliage can create absolutely breathtaking displays in the homelandscape. But what happens when the leaves don’t fall?

What Does Marcescence Mean?

What is marcescence? Have you ever seen a tree that hasretained its leaves through the winter? Depending upon the variety, the treemay be experiencing marcescence. This occurs when some deciduous trees, usuallybeechor oak,fail to drop their leaves. This results in trees that are full or partiallyfull, covered in brown, papery leaves.

Winter marcescence is caused by the lack of enzymes producedby the tree. These enzymes are responsible for producing an abscission layer atthe base of the leaf stem. This layer is what allows the leaf to easily bereleased from the tree. Without this, it is likely that the leaves will “hangon” throughout even the coldest periods of winter.

Reasons for Marcescent Leaves

Though the exact reason for marcescent leaves is not known,there are many theories regarding why some trees may choose to retain theirleaves throughout the winter. Studies have shown that the presence of theseleaves may help to deter feeding by large animals like deer.Less nutrient dense brown leaves surround the buds of the tree and protectthem.

Since marcescent leaves can be observed most commonly injuvenile trees, it is often thought that the process does offer growthadvantages. Smaller trees often receive less sunlight than their tallercounterparts. Slowing the process of leaf loss may be beneficial in maximizinggrowth before winter temperatures arrive.

Other reasons which trees retain leaves suggest thatdropping the leaves later in the winter or early spring helps to ensure that thetrees receive adequate nutrients. This seems especially true in cases where thetrees are grown in poor soil conditions.

Regardless of the reason, trees with winter marcescence canbe a welcome addition to the landscape. Not only can the beautiful leaves offertexture in otherwise bare scenery, they also provide protection for both thetree and native winter wildlife.

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Why Do the Leaves of Some Trees Turn Brown but Not Drop?

Have you noticed a tree around town that holds its brown leaves all winter instead of dropping them?

There's a term for this curious leaf-retention phenomenon. It's called marcescence. And if it's a conical-shaped understory tree with bleached, light tan leaves, it's probably an American beech (Fagus grandiflora).

"Basically, that means that things hold onto stuff," said Jim Finley, a Pennsylvania Extension Service forester who is also a professor of forest resources and director of the Center for Private Forests at Penn State. Marcescence occurs in other trees beyond beech trees. Leaf retention also occurs in many oak species, witch hazel, hornbeam (musclewood) and hophornbeam (ironwood), said Finley, who added that it's more common with smaller trees, or more apparent on the lower branches of larger trees.


Marcescent Leaves Whisper In Winter by Jason Lubar, ISA Board Certified Master Arborist

Walking in the Wissahickon last year during the windy winter months, I was enjoying the solitude when I heard a steady rustling that had been going onfor a while. Focusing on the sound, I could see American beech (Fagus grandifolia) leaves vibrating in the wind. These faded, thin, ghostly leaves created wonderful sounds in the otherwise quiet winter landscape.

I wondered why beech and other tree species, like the Arboretum’s large Bender oak (Quercus x benderi)sometime hold on so tenaciously to their leaves all through the winter months, many to drop only when new growth forcefully pushes them off in the spring.

It turns out that these leaves that don’t want to leave are called marcescent [mahr-sesuhnt].Marcescence is when plant parts, in this case leaves, remain attached to the plant whenwithered. If you walk through the woods in our area in mid-winter, you will find marcescent leaveson a handful of trees, especially young or juvenilespecies such as oaks (Quercus), American beech, eastern hophornbeam(Ostryavirginiana), musclewood (Carpinuscaroliniana), and perhaps maple (Acer). Each species’ leaves are different, and produce a different sound in the breeze. So if you listen closely, you can identify the tree species in the winter without looking, by sound alone.

But what functional or evolutionary adaptation caused this clasping characteristic?There have been many reasons proposed since the word appeared in the early 18th century.

Protection:Some speculate that marcescent leaves protect new buds and deter browsing animals such as deer or the Pleistocene magafauna that existed millions of years ago.The leaves may also absorb and radiate heat from the winter sun, which may provide frost protection or allow limited photosynthesis (energy production) in the chlorophyll under the twig’s thin bark.

Nutrient Boost:Another hypothesis is that releasing leaves in the early spring facilitatesthe release of nutrients to help the tree during the early growing season, whereas those nutrients may have been washed away or leached too far into the soil if the leaves fell and decomposed during the normal leaf drop.

Moisture Management:Others suggest that marcescent leaves can trap snow and reduce the velocity of dry winter winds, leading to more moisture at the tree’s base in the spring.

Regardless of the reasons that marcescent leaves exist, they are a wonderful feature of our winter landscape. Next time you are out in the winter snow near a young American beech, close your eyes and listen. It is remarkable what you will hear.

I leave you with the 2 nd stanza of the poem Reluctance by Robert Frost:


What is MARCESCENT?

This week’s word of the week is MARCESCENT (mar·ces·cent) and was suggested by not just one, but two BYGL readers, Sue Cook and David Sprague. Keep the suggestions coming. We have a nice list of words that keeps on growing.

MARCESCENT defined by dictionary.com is the withering, but not falling off, as a part of a plant. Marcescent comes from marcescere, and in Latin, means “to fade”.

So have you ever noticed leaves on some trees hang on over the winter and sometimes even into the spring, while other deciduous trees lose theirs in the fall? While many may have noticed these leaves in late-fall, it is really evident now in the middle of winter, especially with a white carpet of snow. These dried brown leaves can remain attached, but usually spring growth will ‘encourage’ them to finally fall.

The leaf drop, also referred to as abscission, can happen at different times. It isn't a one size fits all, but rather lots of different ways and times this can occur and can even vary from year to year. Some trees may drop some leaves, but not other. If this occurs, trees will usually drop leaves from their upper canopy, but those lower limbs may hold on to their leaves longer. These persistent leaves do not readily form an abscission layer at the base of the leaf petiole, where it attaches to the twig. This allows these brown leaves to remain attached on trees much longer, often to the chagrin of autumn-rakers who want to rake once a season and be done.

In a typical year, leaf marcescence can often be observed on trees including oaks (Quercus spp.), American beech (Fagus grandifolia), hornbeam (Carpinus caroliniana), Eastern hophornbeam (Ostrya virginiana), and witchhazels (Hamamelis species). These trees can be termed marcescent ‘regulars’, meaning every season the leaves hang on longer which can sometimes cause stress on gardeners who just want to put that rake away in the fall. Instead of swapping that tool out for a snow shovel, they make space for both and sometimes alternating their uses as the leaves finally decide to drop.

Sometimes, marcescence is more pronounced on younger trees, but may be seen only on the lower, more juvenile limbs of larger, more mature trees, especially the oaks. However, a long warm autumn that is quickly followed by the onset of cold weather can prevent the formation of this abscission layer on other tree species as well.

People often wonder if marcescence is either helpful or harmful when it comes to plant health? If there are a lot of leaves present over the winter and snow or strong winds, or the combination of the two, that could have some negative effects and lead to some branch breakage. Some other theories that I discovered while reading about this topic include:

  • Some plant ecologists have suggested that leaves that drop later in the spring will provide a fresh layer of leaf mulch around the tree that helps conserve soil moisture in the spring, and these leaves decompose later during than those that dropped in the fall and will provide additional nutrients for growth in the new season.
  • Another theory that seems to make some sense is tied to wildlife, specifically deer. Experts believe that lower limbs hold onto these dry unpalatable leaves to deter browsing by these four legging “hungry herbivores.” Deer prefer to feed on the more tender and nutritious buds and twigs. It is thought that the bitter old foliage will protect what they really want.


A Marcescent Late Fall

I’m sure you have noticed that many more trees than usual have kept their withered leaves this year. Yes, there is a botanical term for this: marcescent! We had a most beautiful fall but before some trees turned fall color and dropped their leaves we had a deep freeze. In fact, we recorded the coldest November temperature in 20 years!

Virtually all locally native trees (except some oaks that normally hold marcescent leaves) had already dropped their leaves before our deep freeze and were unaffected. Most of the trees that were affected were strains from more southerly climates and their marcescent foliage is a signature that the plant is not fully adapted to our climate. Sweetgums and oaks from Southern sources were the main trees showing the abnormal “freeze-dried” green foliage that was prematurely killed. (Shumard Oaks in the Perennial Garden shown above, image from Dec. 3, 2013.)

Many of our native oaks normally hold marcescent leaves but they never do so while still green. They can be beautiful shades of brown from two-toned tan on Swamp White Oaks (right above) to rich pinkish browns on White Oak and medium brown on Shingle Oaks (left above). I rather like these leaves in the winter landscape and they can be a great place for birds and wildlife to find some shelter. Marcescent oaks can even make good windbreaks! The above image taken Dec. 3, 2013 near the Fountain Garden.

So why do oaks hold their leaves? Since a tree can’t speak we have to make scientific observations to learn why. It appears many oaks hold their leaves into winter to ward off browsing by animals like deer and elk. Hard to imagine that elk once roamed over the entire Midwest! The unpalatable and nutrient poor leaves make it difficult to get to the rich, nutritious buds for next season’s growth at their base. That is also why marcescent foliage is more often observed on younger oak trees or at the base of larger oak trees. The image above is of the lower branch of a rare native hybrid Shingle x Northern Red Oak (Quercus x runcinata) in the Rock & Waterfall Garden. Very few leaves can be found on the higher branches.

One of the downsides of the marcescent fall, especially on Sweetgums is that those trees will now be more likely to catch ice or wet snow and be damaged by a winter storm. None of Powell Gardens’ Sweetgums have this trait and I recommend to buy them in fall and only trees with timely and beautiful fall color. The same can be said for most oaks. The above shows a Sweetgum in normal fall color but shows a glimpse of a tree to its right that was still mostly green — trees that didn’t turn are now covered in marcescent foliage around town.

There is one Missouri Oak that displays a unique trait that is beyond marcescent: it is a fine line between tardily deciduous and semi-evergreen! It’s the Water Oak (Quercus nigra) native across much of the American South and reaching the Missouri boot heel (see the above image of one growing in Blue Springs). Water Oak’s leaves were not killed by this latest freeze and in fact the leaves are hardy down to zero. They gradually color and drop through fall and winter, a few staying alive and green on the tree all winter. Yes, the leaves and the whole tree for that matter can be killed by a severe winter here. It is one oak we don’t yet have in our Powell Gardens collection but we plan to grow a good hardy one grown from the local champion tree which has shown extraordinary hardiness. If you know of a Water Oak in Greater Kansas City let us know — we know of only a handful of trees and they are easy to spot this time of year.


Watch the video: Falling Autumn Leaves Background loop 2 Read Desc


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