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.