Witch Hazel (Hamamelis virginiana) is nature’s final fanfare of the fall. As colorful fall foliage disappears, the yellow strap-like petals of Witch Hazel’s fragrant flowers brighten denuded woods. These 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. (In photo, the yellowish-tan capsules were formed this summer, and the one brown, year-old capsule has opened and dispersed its seeds.)
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The falling of a leaf is the final step in an ordered series of events referred to as senescence. This process allows trees to conserve resources, prepare for a dormant period, and shed inefficient tissues. When leaves become unable to produce food due to a lack of chlorophyll, a process of shutting-down and sealing-off begins. Leaves are shed through a number of biological actions which take place at the base of the leaf’s stem, or petiole. The walls of some cells weaken, while those of other adjacent cells expand. The expansion of the latter causes pressure against the weaker-walled cells, resulting in these two groups of cells tearing away from each other, causing the leaf to fall. The tree forms a protective barrier on the wound where the leaf had been attached to the branch, sealing it off from pests and the environment and leaving a leaf scar.
Even though it snowed in Vermont this weekend, there is something else white and fluffy that is also being blown about, and it doesn’t melt when it hits the ground. The tiny white bits of fluff that are floating in the air are the seeds of aspens (also referred to as poplars), primarily Bigtooth Aspen (Populus grandidentata), that are borne in capsules that develop along a 3 to 6-inch dangling stem. These former flower clusters, and the capsules and seeds they developed into, are referred to as catkins. The capsules split apart when the seeds are mature, releasing the cottony-tufted seeds that are well-designed for dispersal by the wind. Looking into the fluff-filled sky, it’s not hard to believe that a single Bigtooth Aspen tree can produce over a million seeds.
Tree buds are formed in the summer, so if you look at a tree today, it will have buds on it, in the axils of where the leaves used to be (on deciduous trees). There are two kinds of buds – leaf buds and flower buds (flower buds are typically fatter than leaf buds). Both are usually covered with scales which help seal in moisture to protect the bud from drying out during the long, dry winters when water is frozen and therefore unavailable. Different types of trees have different types and numbers of scales. There are a few trees whose buds lack scales completely; these buds are referred to as “naked.” Witch hazel (Hamamelis virginiana), bitternut hickory (Carya cordiformis) and hobblebush (Viburnum lantanoides) all have naked buds. In the photograph, a hobblebush leaf bud is on either side of a flower bud.
American Hornbeam (Carpinus caroliniana) goes by many names, including Musclewood, Bluebeech and Ironwood. Its smooth, gray bark that appears twisted and somewhat muscular is very distinctive. This member of the Birch family usually has several trunks, and is usually less than 30 feet tall. Its fruit is in the form of clusters of small nutlets, each attached to a papery bract. A good seed crop is produced every three to five years, at which time it benefits ruffed grouse, cardinals, evening grosbeaks and American goldfinches, all of whom prefer it over many other seeds.
Witch Hazel (Hamamelis virginiana) is in flower, one to two weeks early this year, just as last year’s fruit is mature and ready to explode, sending seeds flying. This shrub may have gotten its name from its association with dowsing, which was once thought to be a form of witchcraft. (Witch hazel’s branches were once the wood of choice for dowsing rods, whose purpose is to locate water, or “witch” a well.) The bark, leaves, and twigs of witch hazel are all high in tannins, giving this plant astringent properties. It has also been used for any number of medicinal purposes, from treating hemorrhoids to laryngitis.
Many plants practice “delayed greening” of their leaves, including this Red Maple (Acer rubrum). An initial lack of chlorophyll prevents the leaves from photosynthesizing and making food, which means they have little nutritive value, and thus, appeal, to an herbivore. Most plants that delay greening have reddish leaves due to the presence of anthocyanin, a pigment which appears reddish. A majority of herbivorous insects and invertebrates cannot detect colors in the red range of the color spectrum. Young leaves suffer the greatest predation from invertebrate herbivores. Red leaves would be perceived by these leaf eaters as somewhat dark and possibly dead – not a choice food material. It is possible that the red coloration of new leaves allows the plant to make them unappealing to the herbivores that would otherwise eat them.