A short deciduous woodland and thorn bush cover the drier rocky slopes, while acacia trees flower in the taller floodplain forest. Ogaden 

 region, Ethiopia. 



always hot. True enough, if you remain in the low- 

 lands, but conditions change as one ascends the moun- 

 tains. Average temperatures decrease regularly as alti- 

 tude increases. For example, at 2,000 meters elevation 

 (6,500 feet, slightly higher than Denver) afternoon 

 highs average between 70 and 80 degrees F, with night- 

 time lows dropping into the 50's. 



Many higher elevation forests are cloud forests. 

 Warm winds, forced up the mountainsides, cool, lose 

 their ability to hold moisture, and form misting clouds 

 over the forest. The cooler overcast conditions allow 

 air-plants, or epiphytes (plants that use other plants as 

 a support), to grow high among the branches of the 

 trees. The strong winds and weight of the epiphytes 

 cause many branches to break, with the result that the 

 cloud forest is not as tall as a lowland rain forest, and 

 there is more light on the forest floor below. While 

 there may be as much rainfall in montane cloud forests 



as in the lowland rain forests, the two forest types are 

 very different in structure, climate, and species com- 

 position. Cloud forests are where epiphytes achieve 

 their greatest numbers. Orchids, bromeliads, ferns, 

 and mosses festoon the branches of trees in this cool 

 and misty world. 



Higher up the mountains (between 2,000 and 

 3,000 meters), the forest changes yet again. The cooler 

 nights reduce the number of species that can compete 

 in these forests and it is not uncommon to find domi- 

 nant species of trees, something rarely encountered in 

 the lowlands. The cooler temperatures of higher eleva- 

 tions are reflected in the smaller size of leaves and 

 decreasing stature of the forest. In addition, the thin- 

 ner air is a bit drier and mosses and lichens become the 

 major epiphytes. At elevations above 3,000 meters 

 (10,000 feet), night-time temperatures can regularly 

 fall below freezing. These high mountain habitats 



11 



