Hairs protect a leaf from drying, cold and animals. They are common in spring.
On many plants there are tiny hairs that trap a thin layer of air next to the leaf, which protects it from evapotranspiration – they stop the leaf drying out.
The boundary layer of air can also ward off frost, and in some leaves the hairs protect against insect attack. They always have a job to do. In many species, including the beech in my local woods, this downy layer is obvious when the leaves are young, but fades as they mature.
From the book, How to Read a Tree.
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How to Read a Tree – The Book
Autumn Appears First High in Southern Leaves
Leaves Are a Lighter Colour in Early Spring
