If you look on the ground these days as yellow Trembling and Bigtooth Aspen leaves are falling, you may notice that small splotches of green remain in some of them. These chlorophyll-laden patches are usually found near the bottom of the midrib of the leaf. If you open the pocket of tissue at the base of the green section, it’s highly likely you will find a minuscule (2 mm long) translucent caterpillar (a microscope may be necessary to detect it).
The caterpillar (larva) first bores into the stem, or petiole, resulting in a swelling. When it reaches the leaf blade it makes an elongated blotch between the midrib and the first lateral vein. The larva is capable of secreting a chemical which prevents the natural deterioration of the leaf. As a result, chlorophyll is retained in this area and photosynthesis continues to take place, providing the larva with food. The leaf-mining larva (Ectoedemia sp.) will pupate over the winter (outside the leaf) and emerge next spring as a very tiny moth which will feed on the honeydew secreted by aphids. (Photo: Mined Bigtooth Aspen, Populus grandidentata, leaf)
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.
Poplar (also called Aspen) buds are an important winter food source for wildlife, but for none as much as the Ruffed Grouse. During the course of a year, a Ruffed Grouse may feed from as many as 100 species of plants, but in the winter, species of poplar are by far its most important food source. In fact, the relationship between grouse and poplars is such that the range of the Ruffed Grouse is practically identical to the range of Trembling (also known as Quaking) Aspen (Populus tremuloides) and Big-tooth Aspen (Populus grandidentata).
Poplars are dioecious – the male and female flowers grow on separate trees. Although grouse will settle for any poplar bud, it is the male flower buds of Trembling Aspen trees which they prefer, due to the buds’ high amounts of proteins, fats and minerals. (Female buds are smaller and have less nutrients, oddly enough.) Ruffed Grouse seldom feed on a poplar tree that is less than 30 years old. Perhaps these older trees have more vigorous buds, or perhaps their branches are easier to perch on because they are larger. (Information source: Ruffed Grouse: Woodland Drummer by Michael Furtman)
One associates Beavers with a fairly strict diet of bark and twigs. While their winter diet consists primarily of woody plants, they consume a variety of herbaceous and aquatic plants (as well as woody) during the spring, summer and fall months. Shrubs and trees make up roughly half the spring and autumn requirements, but as little as 10% of the summer diet when herbaceous plants such as sedges and aquatic plants become available.
Recent observation of a local active Beaver pond revealed that Interrupted Fern (Osmunda claytoniana), Jewelweed/Touch-Me-Not (Impatiens capensis) and grasses are high on the list of preferred foods of one Beaver family during the summer, although woody plants such as poplars (Populus spp.) and Paper Birch (Betula papyrifera) have also been consumed in fairly large quantities. All too soon Beavers in the Northeast will be limited to the bark of branches they’ve stored under the ice. Until this time, they take advantage of the accessibility of more easily digested herbaceous plants. (Thanks to the Shepards and Demonts for photo op.)
A leaf miner is the larval stage of an insect (primarily moths, sawflies and flies) that feeds on leaf plant tissue. Most of these insects feed for their entire larval period within the leaf, creating tunnels between the upper and lower leaf surfaces. Some will pupate within the leaf mine, while others cut their way out when they are full-grown and pupate in the soil.
The pattern of feeding tunnels, as well as the pattern of droppings, or frass, within them (darker sections of tunnels), combined with the species of plant on which they occur, can sometimes identify the species of insect that created the mines. A moth larva, the Common Aspen Leaf Miner (Phyllocnistis populiella), leaves delicate, serpentine mines (see photo) that are diagnostic of this species.
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)