Why do native plants keep or lose leaves?

Asked January 25, 2020, 10:30 AM EST

I am new to Portland. I've noticed that some broadleaf native plants have leaves in winter (such as blackberries), whereas others are deciduous (such as maples). I understand that conifers, and other plants with smaller, "tough," waxy leaves can withstand freezing conditions. But what determines whether the less "tough" natives keep or lose their leaves? I'm looking for a specific (technical) answer, such as adaptations to light. temperature, moisture, if possible. Thank you for your help!

Multnomah County Oregon

5 Responses

Thank you for your question. The technical answer that applies to all plants is explained in this article: http://www.loyno.edu/lucec/natural-history-writings/abscission-reason-why-leaves-fall You can do more research on abscission and its genetic roots, but the bottom line is that all plants lose their leaves (and needles). Good luck!

Thank you for the very good article on the process of leaf fall. Still, I wonder why some broadleaf plants remain leafy through the Portland winter, while others drop their leaves. Specifically, I wonder about big-leaf maple. Do they have leaves that are less tolerant of freezing temps and snow than, say, blackberries? Or are winter light or temp levels too low overall for the maples to do efficient photosynthesis? Or...?

There are several very technical books and book chapters that explain the “whys” but they are not available online. Here is a preview: https://www.sciencedirect.com/topics/agricultural-and-biological-sciences/abscission Perhaps you’ll find your answer when reading about why maples often do not drop leaves: https://www.arboretum.harvard.edu/leaves-dont-leave/

Thank you again. Your links point in some interesting directions. Certainly, water loss is a problem in many areas in winter, where the water is locked up in ice and snow, and frigid winds blow. Not so much here in lovely Portland! (BTW, trees such as native sycamores in California lose their leaves starting in fall, even though winter is mild and the least dry season.)
I am interested in the idea that being leafless in spring facilitates pollination for some species. However, I've not been here for spring yet to see that.
Or maybe there is some benefit to the maples to have leaf cover on the ground?
Or -- just musing here -- maybe losing old leaves and growing new leaves could help the trees fend off the effects of disease/herbivory or improve photosynthesis. Losing leaves in fall might allow maximum time for the fallen leaves to return nutrients to the soil before new growth.
Anyway, I'll continue to research around, with your articles as a springboard.
Thank you for your ideas!

On the latter note: http://news.mit.edu/2012/leaf-decay-1004 As you research, here is a tip. To get science-based answers, type in “[topic] site:edu”. That will reduce, but may not eliminate, ads and popular literature on the topic, which may or may not be substantiated. Good luck!