Why do some deciduous trees keep their leaves?

Bend, OR(Zone 4b)

The pin oaks that line the streets of our downtown keep their brown leaves all winter. And our big ornamental pear tree hangs on to its leaves (still green) through all kinds of winter weather. The leaves of our hardy almonds and flowering dogwood also persist until late winter/early spring. What would be the evolutionary advantage? And what deciduous trees in your yard keep their leaves?

Scott County, KY(Zone 5b)

For Bend, Oregon - you can't hardly ask those questions of all those species that are not of your area. They are all imports, and will behave differently than they do where they "grew up."

That said: pin oaks (Quercus palustris) have marcescent leaves here, where Pin Oak is a native tree. All the other species you mention (Callery Pear, Hardy Almond, and Flowering Dogwood) are completely deciduous in the Ohio River valley region. So, I'm not sure that your question is entirely valid.

As to why some trees hold old dead leaves through the winter/dormant season (American Beech, Sugar Maple, White Oak, Shingle Oak, and Vernal Witch Hazel are some common species that come to mind for the central US), it may have something to do with the chemical processes in plants that cause complete abscission of these withered plant parts.

Danville, IN

I've always wondered if oaks in particular hold on to their leaves throughout most of the winter months to give them an advantage over pines, spruces, and hemlocks in forest settings. Since conifers can photosynthesize food as long as temperatures are warm enough, even into late fall and early spring, while most deciduous trees shed their leaves in the fall no matter the temps and leaf out late in the spring, this way oaks keep shading out nearby conifers. Gives them an evolutionary "leg up" on evergreens. I've never read anything about this, but seems logical.

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