Northland Nature: Basswood seeds still on trees

Feb. 2—With the obvious exception of conifers, the trees around us now mostly look bare. Pines, spruces, balsams, cedars and junipers continue holding their green needles throughout the winter, being adapted to handle the cold and snow cover.

While scanning the landscape, we might also notice that there are a few deciduous trees that keep their leaves during the cold season. They are definitely a minority and scattered in the woods; it is easy to overlook them. The leaves are curled and brown but remain attached to the stems. Many ironwoods fall into this category and walking some areas of the woods at this time, I am surrounded by these brown-leaved trees.

In addition to this, some sugar maples and red oaks still have leaves. I have noticed that it is the smaller and younger trees that retain the leaves. Perhaps this is a winter adaptation for the newer trees of these species.

To the south of us (within a hundred miles), another oak, the pin oak, keeps leaves through the winter, often thick on the branches. These trees keeping their brown leaves may last until being replaced by the new growth of spring.

But not all the other deciduous trees are bare. Looking at the branches, we might note the presence of bird and squirrel nests and some still hold the products of last summer: fruits, berries and seeds. Perhaps the most obvious of these are the crab apples. Dried and frozen, these little "apples" are still present and are likely to be discovered by birds and small mammals as we progress through the season.

Crab apples may be the most notable, but not alone. Also with berries and fruits are those of highbush cranberry, mountain-ash and sumac. Even a few apples are still with rotted frozen fruits, which may be eaten by hungry birds and squirrels. They may be retained on the branches until spring.

While many trees such as oaks and maples have dropped their seeds, others continue to hold them now in mid-winter. Samaras on box elders, unlike those of maples, can still be seen, as are the winged seeds of ash. Both may be quite numerous. And the strange-looking seeds of basswoods are often on the trees in winter, too.

Recently, after a light snow, I was scanning the branches of trees looking at the build-up on the branches. Until dispersed by wind, the snow hung onto these arboreal sites and made for excellent winter scenes. But when checking a nearby basswood, I noted that the seeds were so thick here that they almost looked like leaves.

Basswood (Tilia americana), also called American linden, is a large native tree and adapted to Northland winters. (Other non-native basswoods grow in the area as well, usually along city streets.) Stumps are often seen with second growths at the base, making for identification in the winter. In summer, trees grow huge, heart-shaped leaves.

On the stems nearby, they produce a group of pale flowers that hang down from a leaf-like structure. Not so colorful, but very aromatic, these late-blooming flowers attract bees. (Last to flower of our trees, basswoods do not bloom until July.) Once pollinated, seeds form where flowers were. The brown ball-shaped seeds, about the size of cherries, stay hanging on this growth after the leaves drop.

Upon falling, the leaf-like structure can hold the cluster of seeds and act like "hand gliders" as they descend. Some drop earlier in the season, but as I saw on this winter day, many also are still attached to these bare deciduous trees.