Figure 1. Alnus incana mature tree (6)
Description:
Alnus incana, more commonly known as the speckled alder, is a dicotyledonous perennial and a member of the Birch family Betulaceae. A. incana is named for its shiny gray bark and its white lenticels that give it its speckled look. The lenticels serve as openings where gas exchange can occur.The speckled alder can be considered a large shrub or a small tree. These plants can reach heights between 10.0 and 24.0 meters (32.8 – 74.7 feet). Its leaves have a dull dark green color on top and a grayish tint with fine hairs under the leaf. A. incana is a deciduous plant and, therefore, loses its leaves during the winter. Speckled alders are very tolerant of cold temperatures as they can withstand temperatures as low as -50.0°F.
Though both sexes may be found on the same plant, Alnus incana is considered to be monoecious as each individual flower has a determined sex, being either male or female. It depends on wind pollination in order to facilitate fertilization. The male structures are called catkins and are usually between 1.5 and 3.5 inches in length.
Figure 2. Depiction of reproductive strugtures (3), leaves (6), and bark with lenticels (6) of Alnus incana
Geographic and Elevation Distribution:
Speckled alders are most commonly found in regions around the Great Lakes and the St. Lawrence River in North America. However, they have now become common in Europe, Northern Asia, and throughout the rest of the North American continent within these continents’ mountainous valleys and sub-arctic forests. In Utah, Alnus incana can be located in elevations between 1,240 and 2,730 meters above sea level.Alnus incana are common understory shrubs and are successful in moist lowlands typically near significant bodies of water. As a result, speckled alders are commonly located near streams and lakes and in riparian zones, marshlands, and nutrient-rich swamps. Although they are typically found in the understory of forests, A. incana grows well under full sunlight conditions.
Ecological Importance:
The lumber derived from Alnus incana may not have commercial importance, but speckled alders do have important ecological uses. They are very commonly used in land reclamation in order to increase the fertility of poor soil. Although they require moisture-rich soil and like to live in nutrient-rich environments, speckled alders have some important biological adaptations that allow them to successfully live in nutrient-poor and disturbed habitats. Their symbiotic association with bacteria from the species Frankia helps speckled alders to fix atmospheric nitrogen. This important biological association helps these plants out-compete many of their competitors and establish in locations where other competing species may not be able to. Alnus incana also have an amazing ability to adapt to a wide variety of soils. They are adapted to acid, neutral, and basic soils. Speckled alders have been seen in locations with soil pH ranging from 4.8 to 7.7, a one-thousand fold difference in acidity.Alnus incana is a very fire-resistant plant. Although the plants may physically die within the fire, they are able to re-germinate from their root crowns if the environmental conditions are favorable. The stems need to be within two inches from the soil surface in order for it to be able to re-establish. Speckled alders also have the ability to delay plant succession in order to increase the ability of itself to re-establish. However, if the fire results in extremely high temperatures, it is possible that the heat from the fire could burn the root crown and extinguish the possibility for the Alnus incana to re-establish.
Alnus incana is also an important source of habitat and food for many species. Small animals such as snowshoe hares use these plants for cover. Many birds use these plants to establish nests in. Larger animals, except moose, use these plants as a source of food.
References:
1. Betulaceae. (2007, November 29). In Wikipedia, The Free Encyclopedia. Retrieved 23:32, November 29, 2007, from http://en.wikipedia.org/w/index.php?title=Betulaceae&oldid=174670842
2. Frankia Home. Retrieved November 14, 2007, from Frankia & Actinorhizal Plants Web site: http://web.uconn.edu/mcbstaff/benson/Frankia/FrankiaHome.htm
3. GreyAlderC. Retrieved November 13, 2007, from Grey Alder Web site: http://www.the-tree.org.uk/BritishTrees/TreeGallery/greyalderc.htm
4. Ramsey, R. D. Alnus incana. Retrieved November 12, 2007, from Digital Atlas of the Vascular Plants of Utah Web site: http://www.gis.usu.edu/Geography-Department/utgeog/utvatlas/family/betu/alin.html
5. Rook, E. J. S. (2004, August 29). Speckled alder, Alnus incana. Retrieved November 12, 2007, from Alnus incana Web site: http://www.rook.org/earl/bwca/nature/shrubs/alnusincana.html
6. Trees of Wisconsin: Alnus incana, speckled alder. Retrieved November 12, 2007, from Trees of Wisconsin Web site: http://www.uwgb.edu/biodiversity/herbarium/trees/alninc01.htm
7. (2002, June 20). pH Scale. Retrieved November 13, 2007, from The pH Scale. Web site: http://staff.jccc.net/PDECELL/chemistry/phscale.html