Quirks & Quarks

Quirks Question: Why do some non-evergreens keep leaves in winter

As the seasons change, some trees buck the trend and keep leaves into winter.
Oak tree in front of National Gallery in Ottawa.

Dr. Madhur Anand is a professor in Global Change and Sustainability at The University of Guelph. She explains:

"The observation that some trees hold onto dead and dry leaves is actually quite normal for some species like oak and beech. There are several hypotheses out there as to why some trees do this. One is that it thought to be an adaptive significance for trees growing on in fertile sites, which could be a means of slowing down the decomposition of the leaves and then providing nutrients to the tree when it's most needed. 

Another hypothesis is that it could be an adaptive significance for trees growing in conditions where water is limiting and keeping these leaves on could allow the tree to trap snow during the winter months. That then becomes available in spring when the snow starts to melt. Well we know that temperature and other climatic variables can affect the timing of obsession processes like the cutting off of the leaves. So I think we can easily imagine a scenario where warmer than usual conditions in September and October could delay the obsession but then the sudden onset of extreme cold can then kill the leaves before they're quite ready to even fall off."