Afroalpine Extremes
As one observes the Ethiopian wolf moving through the landscape of
the upper portions of the Bale Mountains, one's attention is immediately
drawn to the remarkable environment the wolf inhabits. The vegetation
of the Bale mountains differs greatly from the surrounding plains.
In the uppermost elevations, above 4,000 m, a peculiar flora emerges
that is so different from the flora at lower elevations on the same
mountain that it has been treated as a separate floristic region,
referred to as the Afroalpine. Here we describe a sample of the
unique flora and several of its special adaptations to the harsh
conditions of the Afroalpine environment.
Few environments populated by plants on this planet have greater claims to extremes than the Afroalpine belt of East Africa and Ethiopia. The noted botanist Olav Hedberg describes the Afroalpine climate as having "winter every night and summer every day." This characteristic is fundamentally governed by two geographical circumstances, the close proximity to the equator and the high elevations above sea level. The combined effect of intense solar radiation and a thin atmosphere results in pronounced daily temperature extremes. Rapid heating after sunrise and cooling after sunset, as well as the occasional change in cloud cover, can mean violent temperature changes (up to 10 degrees C in less than half an hour). Night frosts are frequent, even in summer, and snow is also common. In fact, glaciers are present in the highest of these mountains, such as Kilimanjaro and Mt. Kenya. In addition to the temperature extremes, dry spells are prevalent and high winds are very common.
Within this extreme environment, you will find very specialized plants that are well adapted to the harsh conditions. On the Sanetti Plateau, the most conspicuous of these unique lifeforms are the giant lobelias. They are characterized by thick, unbranched stems, each carrying a continuously growing, large rosette of leaves, terminated by an immense flower. During the day, the outermost leaves are more or less flat and spread outward to capture sunlight. For protection against the cold nighttime temperatures, the leaves curl inward and are pressed up against the plant to protect the inner shoot. A thick and light colored waxy indumentum covering both sides of the leaves protects them against the intense solar radiation during the day. In other species, a dense pubescence can cover the leaves. The pubescence helps to reflect the intense radiation during the day and diminish outward radiation at night. The waxy surface of the giant lobelia leaves may also serve as a reflector in this regard. The giant lobelia is just one example of the array of specialized plants adapted to the harsh conditions of the Afroalpine. Return to Flora Home Page |
