A biome is a distinct biological community that has common characteristics for the environment they live in. Worldwide there are five major biomes – aquatic, desert, tundra, grassland and forest. On a smaller scale, biomes may refer to areas where the predominant vegetation is characterized by adaptations to the particular local environment. For example, Howell’s marsh marigold plants (discussed in my previous post “Howell’s Marsh Marigold” on 12-13-2017) has adapted to live in wet habitats.
An ecotone is a transition area between two biomes where two communities meet and integrate. The boundary between the two communities may be narrow or wide, local or regional. This transition zone results when physical properties, such as soil type, moisture, light and temperature to name a few, undergo a change over a relatively narrow area. Differing species on either side signal an ecotone.
A ecotone is easily visible in a portion of our property that is set aside as a wildlife area (Modoc County CA). There is a small hillock with deep, well-drained soil surrounded by clayey, poorly drained soil. As seen in the photograph, atop the hillock are tall, grey-green sagebrush plants, while the sagebrush plants surrounding the hill are smaller and do not have a greenish color. Near the bottom of the hillock a line separating the two is distinctly visible. That line is a sagebrush ecotone.
The sagebrush atop the hillock is tall sagebrush (Artemisia tridentata) while silver sagebrush (Artemisia cana) surrounds the hill. Tall sagebrush is adapted to deep, well-drained soils while silver sagebrush grows in clayey, poorly drained soil or in standing water. Where the more fertile, drier soil of the hillock changes to wet, less fertile soil of the surrounding area the plant biome changes – a sagebrush ecotone.
Settlers in the 19th Century recognized that the presence of tall sagebrush indicated good agricultural soil and chose the sites for their farms accordingly.
More information about tall and silver sagebrush can be found in my previous posts: “After the Storm” on 09-17-2011 and “Silver Sagebrush” on 12-06-2013.