An online resource based on the award-winning nature guide

Trees

Eastern Cottonwoods & European Honey Bees

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One species of tree you might encounter if you’re in a floodplain is the Eastern Cottonwood (Populus deltoids), a member of the Willow family and the Poplar genus. Because it can tolerate flooding, it often grows near river banks and disturbed wet areas. The buds of Eastern Cottonwood are large and somewhat sticky, due to the resin that they contain. Resin exudes from the buds during the fall as well as the spring, and is evident even in winter when you see it frozen in droplets on the buds (see photo). In trees, resin serves to seal wounds and defend against bacteria, fungi and insects.

European Honey Bees discovered that the properties of cottonwood resin which benefitted cottonwood trees could also benefit them. They collect the resin from the outside of Eastern Cottonwood buds, mix it with wax and apply it to the walls of their nest cavity. This “bee glue” is referred to as propolis, and, as it turns out, serves as an antimicrobial barrier as well as a sealant. Various bacteria, fungi and other harmful microbes are kept at bay by the resin contained in propolis. It also directly reduces two diseases of Honey Bees, chalkbrood and American foulbrood.

Interestingly, if a mouse or small rodent happens to die inside a hive, and the bees can’t remove it through the hive entrance, they often seal the carcass inside an envelope of propolis.  This prevents the hive from being affected by the mouse’s decomposition.

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Distinguishing the Hornbeams

1-23-17-hophornbeam-img_5028There are two trees, both in the Birch family, which, due to the similarity of their common names, are occasionally mixed up with each other. One is known as American Hornbeam (Carpinus caroliniana) and the other as American or Eastern Hophornbeam (Ostrya virginiana). Due to the hardness of their wood, they also both go by the name Ironwood, adding to the confusion. A perfect example of when Linnaeus’s binomial system, which gives each species two scientific names, one of which is unique to each species, is helpful.

While the fruits and leaves of both species are superficially similar, their respective bark is very different. Carpinus caroliniana’s bark resembles flexed muscles (see   https://naturallycuriouswithmaryholland.wordpress.com/2012/10/30/american-hornbeam/ ), earning it yet another common name, Musclewood, while Ostrya virginiana’s bark (pictured)  has a “shreddy” appearance, with the bark broken into small, narrow plates which curve away from the trunk. Look for C. caroliniana in valleys and along streams, and O. virginiana on well-drained slopes and ridges.

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Black Cherry Gum

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When the inner walls of cambium cells in a Black Cherry (Prunus serotina) tree (and other members of the Rosaceae family) are damaged by insects, enzymes can break down pectin, producing jelly-like lumps of clear sap that appear from beneath the bark. This “gum” is often the result of aborted attacks by bark beetles, particularly the peach bark beetle, for the tree uses it to seal off infection. Both direct feeding by insects as well as the process of egg-laying can cause this phenomenon called gummosis. Other factors, including fungi, stress and physical injury to a tree, can produce this reaction.

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Witch-hazel Cone Gall Aphids Laying Eggs

10-26-16-witch-hazel-gall-s20161017_5388At this time of year there is a species of aphid, Hormaphis hamamelidis, that is laying eggs on Witch-hazel branches. Next spring female aphids will hatch out of these eggs and begin feeding on newly-emerged Witch-hazel leaves. The aphids inject the leaf with a substance that causes the leaf to form a cone-shaped growth, or gall, around the insect, providing it with both food and shelter. The galls are hollow, and have openings extending out through the leaves’ lower surfaces. Within the galls the unmated female aphids produce 50 – 70 young. Eventually the galls fill with winged female aphids which emerge through the cone openings, disperse, and repeat the process. The third generation of aphids consists of both males and females which mate and lay their eggs on Witch-hazel. The aphids that hatch from these eggs create the conical galls found on Witch-hazel leaves.

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Abscission Layers Forming

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As the days grow shorter and the nights longer, cells near where a leaf’s stem joins a tree’s branch start to divide rapidly. This is the start of the creation of the corky layer of cells known as the abcission layer.

The annual growth of a tree ends with the formation of the abcission layer. This layer prevents the transport of materials such as carbohydrates from the leaf to the branch and it blocks the flow of minerals from the roots into the leaves. Chlorophyll, critical to the process of photosynthesis, breaks down with exposure to light and is replaced continually by the leaves during the summer. When the abcission layer forms, this is no longer possible.  The chlorophyll slowly breaks down and disappears, revealing the underlying xanthophylls (yellow pigments) and carotenoids (orange pigments) that the chlorophyll was masking. These pigments, in addition to the red pigments (anthocyanins) that are manufactured from sugars trapped in the leaf, provide us with our brilliant foliage.

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Witch Hazel Flowering

witch-hazel-20160917_0860Witch Hazel (Hamamelis virginiana) is nature’s final fanfare of the fall. As colorful fall foliage begins to disappear, the yellow strap-like petals of Witch Hazel’s fragrant flowers brighten denuded woods. This year, with a somewhat late peak foliage, they are both providing brilliant colors to the landscape at the same time.

Witch Hazel flowers are pollinated by moths that are still active this late in the season, and develop into small, hard capsules that remain dormant throughout the winter. During the following summer, these capsules develop to the point where they expel two shiny black seeds 10 to 20 feet away from the tree. The seeds take another year to germinate, making the length of time from flowering to germination approximately two years.

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More Buds

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The previous “bud scale” post engaged readers to an extent that made me feel another post with additional buds to scrutinize would be welcome. Apologies to non-woody plant aficionados!

When identifying woody plants in winter, one takes advantage of everything a tree or shrub has to tell you: bud/branch arrangement (opposite/alternate), bark, silhouette and terminal buds. Buds are so revealing that they alone can immediately tell you what species you are seeking to identify. Is there one bud at the tip of each branch (willows) or multiple terminal buds (red oak)? Are there bud scales (no-witch hazel; yes- bigtooth aspen)? If so, what are their number (willows – one) and arrangement (overlapping, like shingles – red oak)? Are the buds red (striped maple), brown (witch hazel), yellow (bitternut hickory), green, or some combination of these colors? Are they pointed (bigtooth aspen) or rounded (willow)? Every species of tree has buds with a unique combination of these characteristics.  Now is the time to observe them, as some will soon start to open.

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