In the past five years an odd phenomenon has been observed on the bark of over twenty species of trees in New England — an intense reddish-orange coloration. It’s been determined that this is due to the presence of a microscopic green algae (Chlorophyta), tentatively identified as belonging to the genus Trentepohlia. A branching mat of thick-walled algal cells containing a bright orange-red pigment alters the color of the bark.
Red Bark Phenomenon is especially prevalent on White Pine, Eastern Hemlock, Red Oak and American Beech trees. Affected trees appear to be of varying ages and are often, but not exclusively,observed near bodies of water, such as swamps and rivers. Frequently (as pictured) only one side of a tree is affected.
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Beechnuts, high in protein and fat, are the primary fall and winter food for many forest wildlife species including Red, Gray and Flying Squirrels, Eastern Chipmunks, Black Bears, Blue Jays, Tufted Titmice, Wild Turkeys, and Ruffed and Spruce Grouse. The dependence of these animals on this food source makes them vulnerable to the American Beech’s cyclical nut production.
In the Northeast, American Beech (Fagus grandifolia) mast crops (amount of beechnuts produced by beech trees) have a two-year cycle: one year they produce an overabundance of nuts and the following year very few. Among other animals, Black Bears rely on these nuts to sustain themselves over the winter. That a bear’s nutritional health affects its reproductive health was documented in a study in Maine that showed that the mean proportion of female bears producing cubs decreased to 22% when a denning period followed a poor beechnut crop. During denning periods following good beechnut production, 80% of the productively available females produced cubs.
Many American Beech trees in the Northeast suffer from Beech Bark Disease which has seriously compromised their ability to produce nuts. Invasive scale insects (Cryptococcus fagisuga) invade a tree. Through a presently unknown mechanism, excessive feeding by these insects causes two different fungi (Neonectria faginata and Neonectria ditissima) to produce annual cankers on the bark of the tree. This disease decreases nut production, and eventually lesions around the tree girdle it and causes the tree’s death. The diminishing number of healthy beech trees will have a significant effect on consumers of beechnuts as well as a broad array of other organisms.
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The Tulip Tree,(Liriodendron tulipifera), one of our largest native trees, is a member of the magnolia family. There may not be a more appropriately-named tree in all the land, for the likeness of its orange and yellow goblet-like flowers and the shape of its leaves to that of tulips is undeniable. Although large in size (2” in length) the flowers can go unnoticed because they are usually found high up on the 60 – 90-foot tree, and they don’t appear until the leaves are fully developed.
Tulip Trees flower for only two to six weeks. Pollination must occur when the flowers are young, and they are often receptive only for 12 to 24 hours. The flowers produce large quantities of nectar for pollinating insects such as flies, beetles, honey bees and bumblebees, but they are not very efficient pollinators and many seeds do not develop. Those that do form cone-shaped seed heads that may remain on the tree after the leaves have fallen.
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Because tree buds tend to swell and increase greatly in size in the spring, this is often the season when we first notice them and assume that this is when they are produced. However, if you look in the axils of leaves on any deciduous tree right now, you will see full-size buds that were formed this summer. These little packages of miniature leaves, branches and sometimes flowers, will remain on trees all winter, tightly closed and often protected from the elements by modified leaves called bud scales. Come spring, when trees are once again taking up quantities of water, their buds will swell, scales will fall off (leaving bud scale scars), and tiny, pristine leaves or flowers will appear. (Photo is of American beech, Fagus grandifolia, bud.)
Just a quick reminder that the NC Calendar ordering deadline is November 10th.
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Congratulations to “Deb” – the first person to correctly identify the subject of the most recent Mystery Photo as young Eastern Black Walnuts!
Eastern Black Walnuts (Juglans nigra) produce abundant tiny male flowers on long, dangling, finger-like catkins. Female flowers, located on the same tree as male flowers, are fewer in number and are slightly larger. Being wind-pollinated, Black Walnut produces female flowers with stigmas (the top-most, pollen-receiving structures) which have a large surface area designed to catch pollen drifting in the wind. (These are the “rabbit ears.”) The stigmas often persist while the fruit matures — they are barely visible on the left walnut in photo.
By September, the walnuts will have matured. They then fall to the ground where their outer husk slowly decays. The fruits are well-known for leaching chemicals into the soil that inhibit the growth of other plants, an interaction known as “allelopathy” (literally meaning “making your neighbor sick”).
The fruits of the Hophornbeam tree (Ostrya virginiana), also known as Ironwood for its strong, hard wood, are drooping clusters of papery, bladder-like sacs each containing a nutlet. The “hop” portion of its name refers to the resemblance of these fruits to those of true hops that are used in the production of beer. Hornbeam refers to a related European tree whose wood was used to yoke oxen; therefore, its American counterpart wood was also used as a “beam” with which to yoke “horned” beasts of burden.
Striped Maple (Acer pensylvanicum), named after the vertical white streaks on its bark, is often associated with Moose and White-tailed Deer, both of which feed on its bark. In some places it goes by the name “Moosewood” for this very reason. The shape of its leaves give it another common name, “Goosefoot Maple.” In the spring when Striped Maples are nearly in full leaf, bright yellow bell-shaped flowers appear on long, pendulous strings, or racemes. (The flower stalks of the similar Mountain Maple also materialize after the leaves have matured, but these flower clusters are upright, held above the surrounding leaves.)
Striped Maples have the unusual ability to change sexes repeatedly over their lifetime (as does Jack-in-the-Pulpit), a phenomenon called gender diphasy. Among five study populations located in New Jersey, approximately one in four trees exhibited a change in the sex of its flowers between flowering seasons. The flowers of most Striped Maples are predominantly male. If changes occur in the canopy and new conditions seem favorable, a predominantly male tree can become predominantly female (and vice versa, if conditions deteriorate). Size, injury, and carbohydrate reserves are thought to impact the frequency and direction of gender change. Another unusual trait of Striped Maples is that the final sex of a flower is determined within one month of flowering, in contrast to most woody perennials which set buds the previous year.
In 1935 Walter Rogers wrote a book on tree flowers (Tree Flowers of Forest, Park and Street) in which he described White Ash (Fraxinus americana) in the following words. “The Ashes are important trees with interesting features of form and foliage, but their flowers are among the least interesting.” I am of a different opinion, at least regarding White Ash’s male, or staminate, flowers.
White Ash is dioecius – individual trees have all male or all female flowers. Just before and as the tree is leafing out, the flower buds, located on the shoots of the previous season, begin to open. Male flowers are more noticeable than female flowers, partly because of the size of their clusters — there are between 200 and 300 flowers in each cluster – and their vibrant color (which resembles the fall color of some White Ash leaves). Being wind-pollinated, White Ash’s flowers lack petals as they would impede pollination. The stamens are a purplish-red, raspberry-like color until they mature, at which time the pollen’s yellow color is predominant. The flowers are soon hidden by emerging leaves, so now is the time to see if you agree with Mr. Rogers!
Aspens, cottonwoods, poplars – all are names for certain species of trees in the genus Populus. These trees, as well as birch, hickory, oak and willow trees, produce their flowers on spikes called catkins. Telling the catkins of these trees from one another is challenging, to say the least, yet some of NC’s readers correctly identified the catkins in the photograph as those of Bigtooth Aspen, Populus grandidentata. This tree blooms for one to two weeks in the spring and its mature male catkins open and extend to two to four inches in length. The wind, as opposed to insects, disperses the light, fluffy yellow pollen as the catkins dangle in the breeze. Some of the pollen remains intact even after the tree has shed its spent catkins onto the ground.
Because Bigtooth Aspen, and most species of Populus, are dioecious (male and female flowers develop on separate trees), there are only male flowers in this photo and beneath this tree. After fertilization, female flowers remain on the tree and form capsules which contain several small seeds embedded in tufts of fine, white hair. They will fill the air in several weeks looking like bits of floating cotton.
Red Maples (Acer rubrum) are celebrated in the fall for their vibrant colors, but they produce equally vibrant reds and yellows in early spring when they are flowering. Most Red Maples have dense clusters of either male flowers or female flowers (dioecious), although some have both male and female flowers (monoecious). Under certain conditions, a Red Maple tree can sometimes switch from male to female, male to both male and female (hermaphroditic), and hermaphroditic to female.
The showier male, or staminate, flowers contain between four and twelve stamens, with long, slender filaments and red (young) or yellow (mature) anthers at their tips. Both red sepals and petals can be seen at the base of the stamens. A staminate Red Maple in full bloom is a blaze of gold and red. (Photo: mature staminate Red Maple flowers)
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.
There 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.
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.
At 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.
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.
Witch 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.
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.
Much of this coming summer’s woody plant growth is contained in embryonic form inside a tree’s buds. Buds contain an undeveloped shoot, leaf, and/or flower. Formed last summer, these buds must survive the freezing and fluctuating temperatures, relatively dry air and the potential insect, bird and fungal damage that may occur during the fall, winter and early spring.
Bud scales, which are small, modified leaves, cover and protect many of these buds. The number of scales, their arrangement, color, presence or absence of hairs or sticky substances are often distinctive. Willows have one visible bud scale (actually two fused into one), whereas pine and fir buds may have anywhere from 100 to 350. The scales on a bud can either be arranged in pairs facing each other edgewise (American Basswood, pictured) or overlapping like shingles (Sugar Maple, pictured). Colors range from the wine-colored bud scales of Striped Maple to the mustard yellow Bitternut Hickory scales. The texture of bud scales has great variation, including the satiny-smooth hairy bud scales of Box Elder (pictured). Many bud scales, such as poplars, are covered by a gummy substance which serves as added protection.
A few trees and shrubs have buds that lack scales. These are referred to as “naked” buds, and often the embryonic leaves are quite hairy. Witch Hazel, Hobblebush and Staghorn Sumac (pictured) are species of woody plants lacking bud scales.
Most buds have multiple scales which, upon falling off when the bud opens, leave a series of horizontally-elongated scars on the surface of the growing stem. By means of these scars one can determine the age of a young branch, since each year’s growth ends in the formation of a terminal bud which produces an additional group of bud scale scars. Continued growth of the branch causes these scars to be indistinguishable after a few years so that the age of older branches cannot be determined by this means.
Paper birch (Betula papyrifera) produces separate male and female flowers on the same tree, both in the form of catkins (cylindrical clusters of flowers). The catkins form in the fall and overwinter in a dormant state. In the spring they mature as the leaves develop, becoming pendulous. Male catkins are 2-4 inches long, whereas female catkins are usually 1 – 2 inches long. Both lack petals, enhancing wind pollination. After fertilization occurs, the male catkins wither away, while the female catkins droop downward and become cone-like.
The female catkins consist of tiny winged nutlets that are located behind three-lobed, hardened, modified leaves called bracts (yesterday’s blog post) and are usually dispersed by the wind during the fall and early winter. Birch bracts are species-specific — different species of birch have different-shaped bracts, allowing one to identify the species of birch that a bract comes from.
Black Cherry, more than most tree species, often has several identifying features even after it loses its leaves. The buds of Black Cherry have about ten scales, each of which is brown at the tip and green at the base. The bark of young Black Cherry trees is typically smooth, reddish in color and covered with grayish, horizontal lines called lenticels — small openings that allow the passage of gases in and out of the tree. The bark on older Black Cherry trees consists of squarish scales, curved outward at their vertical edges, somewhat resembling burnt potato chips. Black Cherry is one of several trees on which the fungus Apiosporina morbosa causes Black Knot Galls. Lastly, Black Cherry is the primary host for the Eastern Tent Caterpillar moth. These moths encircle Black Cherry branches with their egg masses, and the eggs hatch just as Black Cherry’s leaves emerge from their buds, providing food for the young larvae.
The flower buds of Trembling Aspen (Populus tremuloides) look a lot like pussy willows when they first open up and the tip of the catkins (flower spikes) emerge. Long before the leaf buds open, the flower buds swell and their scales open to reveal male and female flowers that mature into pendulous catkins (male and female catkins are on separate trees). In a month or so, after pollination, the seeds that have developed on the female catkins will be dispersed by the wind and the air will be filled with cottony fluff. (photo: male Trembling Aspen catkins)
Cold nights and warm, sunny days increase the amount of the sap flow in a Maple Sugar tree, making weather an important factor in the quality of a sugaring season. But it’s not the only factor. Both the amount of sap flowing as well as its sugar content affect a given season’s maple syrup production.
Recent research indicates that the size of a tree’s seed crop in the fall is a good predictor of the sugar content of its sap the following spring. A tree, through photosynthesis, produces and stores a given amount of carbohydrates. These carbohydrates are utilized in the production of seeds as well as the production of sugar. Once the carbohydrates are used up, over a year is needed for the tree to replace them. If a lot of seeds are produced in the fall, there are fewer carbohydrates available for the production of sugar the following spring. Hence, while the weather in a given spring may be conducive for the ample flow of sap, the sap that flows may have a very low sugar content if a tree produced a lot of seeds the previous fall, making it necessary to boil more sap to achieve the desired sugar content in the maple syrup. (Source: Northern Woodlands magazine)
White ash, Fraxinus americana, is relatively easy to identify in winter, between its stout, opposite branches and buds and the corky ridges that form diamond shapes on its bark. There are several species of ashes, however, and one feature that distinguishes White Ash is the shape of its leaf scars (located beneath leaf buds) on well-developed branches. Each leaf scar (left by a leaf that fell off the tree) is round at the bottom and notched at the top, resembling the letter “C” on its side. (No other ash has c-shaped leaf scars.) It is often concave along the upper edge and the lateral buds are located within the curved portion of the leaf scar.