A Comparison of Montane and Lowland Rain Forest in Ecuador: II. The Climate and its Effects on the Distribution and Physiognomy of the Forests

Abstract

The climates of 2 rain forest sites, 1 montane (altitude 1710 m) and 1 low-land (altitude 380 m) are described. There is a cooler, wetter season at both, lasting approximately from April to July. Detailed observations were made on the temperature and relative humidity during 3 wk. periods in the undergrowth of the 2 forests and also in large clearings where the conditions are believed to approximate those in the upper part of the forest canopy. The results probably represent a generally valid comparison of montane and lowland forest climates in the part of Ecuador visited. The importance and general occurrence of dry periods as well as frequent fog, even in Upper Montane Forest, is stressed. The factors controlling the distribution of the 3 rain formation-types on tropical mountains (Lowland, Lower Montane and Upper Montane) are discussed. A consideration of the Massenerhebung effect leads to the conclusion that the forest types are primarily correlated with the frequency of fog (stratus or cumulus cloud close to the ground) rather than with any aspect of the temperature regima. The Massenerhebung effect arises in the tropics because clouds form at lower altitudes where the air masses are moister before lifting and cooling, i.e. when over the sea or approaching the foothills of a large massif. Exposure to high winds and soil factors are important in producing stunted facies of each of the three types, including so-called "Elfin woodland". The greater abundance of epiphytes in the montane forest than in the lowland is related to the more frequent wetting with liquid water from fog rather than to a constantly higher humidity.