Signs of spring: Samaras germinating
So many signs of spring! Some are big and glaring like the return of the dawn chorus, warm weather, or lengthening days, and others are subtle and easily overlooked. I typically miss sugar maple seeds germinating since I don’t spend much time in woods where sugar maples thrive, so I was delighted to find this little germinated sugar maple samara at Ethan Allen Park last week. Most of our maples overwinter their propagules as seeds and germinate the following spring rather than produce and drop seeds in the spring.
Here’s the general plan for most of our maples (see table below for a quick comparison): the species flowers in late spring to early summer, with the seeds ripening by summer/early fall. The seeds drop in autumn before trees lose their leaves. Deciduous trees then shed their leaves which blanket the recently fallen seeds, giving them a relatively warm shelter for the cold winter months. Those patient seeds that have survived without being eaten by squirrels or killed by cold temperatures then germinate in the spring. The cold weather in fact allows them to germinate; sugar maple need to be exposed to 100s of hours of sub-freezing temperatures (called stratification) before they’ll germinate.
The notable exceptions to this life history strategy are red and silver maples. These are among the first trees to flower each spring. The seeds then develop and ripen within a few short weeks after pollination and are then dispersed. In the image above you can see the tiny seeds developing even before the leaves fully emerge. Silver maples, which are a riparian species, time their seed drop with spring flooding. The seeds are only viable for a few short weeks, and the flooding both disperses the seeds down stream and ensures that the seeds don’t land in areas that might be dry one part of the year but totally inundated at other times. In the image below, you can see hundreds of silver maple seedlings are deposited at the high water mark of flooding along the Winooski River.
|Species||Flowers||Seed Ripens||Germinates||Persistent in winter?|
|Boxelder||Spring, as the leaves are developing||Fall||Following spring||Frequently|
|Mountain maple||June, after the leaves||Fall||Following spring||Occasionally|
|Norway maple||Spring, before the leaves||Fall||Following spring||Nope|
|Red maple||Early spring, well before leaves||Spring||Spring||Nope|
|Silver maple||Early spring, well before leaves||Spring||Spring||Nope|
|Striped maple||Spring, before the leaves||Fall||Following spring||Nope|
|Sugar maple||Spring, before the leaves||Fall||Following spring||Nope|