marcescent [ mahr-SES-uhnt ] adjective: remaining attached although withered (leaves, petals, sepals)
As much as we may delight in the colors of autumn foliage, we may not find equal pleasure in raking up the fallen leaves, as it is often not a task once and done. Deciduous trees shed their leaves in autumn as they prepare for the severity of winter. Leaves fall off without harming the tree because a separation (abscission) layer forms between the leafstalk (petiole) and the branch. Yet, some trees seem to be laggards and hold on to their dead leaves until new growth dislodges them in spring. These marcescent leaves persist because the separation layer fails to form or complete formation.
Is this cause for concern? Leaf marcescence in winter is most common to specific species: Carpinus caroliniana (American hornbeam), Fagus grandifolia (American beech), Hamamelis (witch hazels), Ostrya virginiana (Eastern hop-hornbeam) and Quercus (oaks). Dead leaves may persist on younger trees or the lower branches of more mature trees, most often oaks. However, dead leaves that appear during the growing season are most likely an indication of a stressed or diseased branch or tree or insect damage (see Managing Cicada Damage to Trees) and should be examined.
Marcescent leaves cover a native Quercus rubra (northern red oak) sapling on Fairlington Community Center grounds in January. Photo © Mary Free 
Some leaves remain on the lower crown of Quercus palustris (pin oak) on a snowy Mount Vernon Trail in January. Photo © Christa Watters 
Marcescent leaves cover this small Quercus alba (white oak) tree in the Fairlington Historic District, Virginia in January. Photo © Mary Free 
Only lower branches retain leaves on a mature Quercus alba (white oak) in Bon Air Park’s Sunny Garden in February. Photo © Elaine Mills 
Marcescent leaves on a young native Fagus grandifolia (American beech) at the U.S. National Arboretum in March. Photo © Elaine Mills
Why do some trees retain their leaves in winter? Weather may be a factor when species other than those mentioned above experience marcescence, but no one knows for certain what benefit it is for those trees that routinely exhibit this characteristic. Some suggest that the marcescent leaves are a defense mechanism. The dead leaves, which surround tasty buds and young shoots, are unpalatable and rustle when disturbed, perhaps deterring browsers during the tree’s younger years when lower branches are most vulnerable. As for the marcescent leaves on the branches too high for determined deer, moose, and elk to reach—Doug Tallamy points out that most would have been within the reach of browsing mammoths and sloths that lived more than 10,000 years ago. After all, oak trees have existed in North America for about 44 million years. Others speculate that spring leaf drop decomposes in time to release nutrients during the plant’s growth period. What is known is that for some species, marcescence is a natural occurrence and some of us will have to break out our rakes or leaf blowers again in spring.
References
Salisbury KV. 2014. Why Do You Just Keep Me Hanging On? PennState Extension. (accessed December 2, 2020).
Tallamy DW. 2021. The Nature of Oaks. pp. 27–28. Timber Press, Portland, OR.
Williamson J. 2019. Winter Leaf Marcescence. HGIC Horticulture Extension. Clemson University.