Scientific Results of the BRYOTROP Expeditioni to Zaire and Rwanda 1. The ecology of epiphytic bryophytes on Mt. Kahuzi (Zaire)

Abstract

Along a transect from 900 m to 3300m elevation, various ecological parameters concerning epiphytic bryophytes have been studiesd. The most characteristic life form between 900 and 2300 m elevation is the dendroid, which is interpreted as an adaptation to better gas exchange under the unfavourable conditions (low light, high air humidity) of the rain forest. Above 2500 m, cushions are the predominant lif form. The cushion are 2-5 cm high but can reach 50 cm at the forest line. In spectacular cases, moss balls are formed up to 1 m in diameter. PH measurements of the bark of host trees revealed values between 4.1 and 6.2, which is in accordance with result from South America and SE-Asia. The bryophyte cover on soil is very low (<5%) below 2700 m but raises to 90% in the subalpine ericaceous belt, but not in the subalpine Senecio-belt. The percentage cover of bryophytes on bark increases from 5 to 80% in the transect with increasing elevation, and the light intensity increases from <1% to 50%. The mean annual temerature decreases continously from 20.6°C at 900 m elevation to 2.5° at 4500 m elevation. This allows a comparison of the growth conditions of bryohyte species occurring disjunct in the oceanic parts of the temperate regions and the tropical mountains. The phytomass of epiphytic bryophytes per m² and per ha increases synchronously in the transect. There is a sudden increase from 8-44 kg/ha in 900-1300 m to 100-600 kg/ha in elevationis between 1900 and 2900 m. Maximum values of 6 tonnes/ha are found at the forest line , being 750 time higher than the lowest value in the lower part of the transect. The water storing capacity of epiphytic bryophytes is 20-60 1/h at elevations between 900 and 1300 m, 130-2000 1/ha between 1900 and 2900 m and 18000 1/ha at the forest line. The latter is 18% of the estimated rainfall.