Flowering Periodicity at Four Altitudinal Levels in Eastern Ethiopia

This report compares flowering seasons in perennial woody plants at four altitudinal levels in the Harar Highlands of eastern Ethiopia. In this area a majority of woody species flower in the dry season only in the montane evergreen forest formation above about 2200 meters altitude. In the other three deciduous formations at lower altitudes flowering is primarily in the wet season. In the drier Acacia (microphyll) formations there is a burst of flowering at the beginning of the rainy season. THE AREA OF the Harar Highlands in eastern Ethiopia above 1000 m altitude and north of latitude 80 30' North experiences a single wet season with two maxima, in April and August. The that fall between March and June are called the rains by local people. They may be heavy but vary greatly from year to year and are dependable for agriculture only above about 2200 m elevation. The months of July, August, and September are the period of the big rains, and these permit the maturation of long-season (90 day) crops at altitudes of about 1700 m and higher. The long dry season, from early October to March or April, may total as little as 50 mm of rain at 2000 m elevation. The dry season in this area of Ethiopia is made more severe by the nature of the prevailing winds. From late September or early October to March the winds are usually quite strong out of the north and northeast. They are part of a large monsoon system bordering the Indian Ocean and sweep across parts of Arabia before moving southward over Ethiopia and Somalia. These winds are thus very dry. The ameliorating effects of higher elevations are pronounced and produce several easily distinguished vegetation types or life zones. The vegetation types in this area range from subdesert grasslands at 700 to 1000 m altitude to elfin forest and subalpine formations above 3000 m. The boundaries of these