Ecological Studies in Four Contrasting Lowland Rain Forests in Gunung Mulu National Park, Sarawak: III. Decomposition Processes and Nutrient Losses from Leaf Litter

Abstract

SUMMARY (1) Measurements of soil respiration, leaf litter decomposition and litterfall-standing crop quotients were made during one year in three rain forest types in Gunung Mulu National Park, Sarawak: alluvial forest (AF), dipterocarp forest (DF) and heath forest (HF). Comparative studies were also made in forest over limestone (LF) over a 6-month period. (2) At the three main sites soil respiration rates showed considerable variation which was not attributable to changes of soil temperature or moisture. Mean annual soil temperatures in the litter layers on the four sites fell within the range 24.3-25.6 IC and mean values for sampling occasions varied less than 1 OC over the year. Mean soil moisture values (wet wt) at 0-5 cm depth, of 60% (AF), 63% (DF) and 73% (HF) varied within 10%. The mean soil moisture of the limestone site was 71%. There was some evidence of a seasonal relationship between rainfall and soil respiration rates in the DF and HF. It is concluded on other evidence that soil respiration mainly represents CO2 efflux from the surface litter layers and the root mat. (3) Chemical analysis of freshly fallen, mixed leaf litter from each site showed the following ranges of element concentration (mg g-1): N, 4.4-11.0; P, 0.06-0-41; K, 0.9-3.8; Na, 0.03-0.11; Ca, 3.7-35.0; and Mg, 1 1-2.7. Concentrations inFicus and Parashorea from the AF were at the upper limits of these ranges except for Na (0.02) and P in Ficus (0. 72). Lignin concentration varied between 31% and 40% for the mixed leaves and between 27% and 28% for Parashorea and Ficus. The highest concentration of polyphenols was in the leaves from HF and the lowest in leaves from the LF, but Parashorea had the highest overall concentration and Ficus the lowest. (4) Weight losses after 10 months from mixed leaves in fine-mesh (40,um) litter bags were 41% (AF), 44% (DF) and 55% (HF). Mixed leaves in the LF showed lower weight losses over 6 months than leaves in the other sites over the same period. Weight losses were 67-75% for Ficus and 49-61% from Parashorea in the three main sites. Weight losses from coarse-mesh (20-40 mm) bags were ranked LF > DF > HF > AF and were not related to total population of litter feeding invertebrates or to the population of individual groups. (5) Litterfall-standing crop quotients (kL values) for leaves ranged from 1 . 7 (AF, DF and LF) to 1.4 (HF) and, for total small litter, were 1.7 (AF), 1.5 (LF), 1.3 (DF) and 1.3 (HF). The kL values for total litter, including wood 2-10 cm, ranged from 0.8 to 1.2 The litter kL values show no obvious relationship to estimated organic matter standing crop in the top 30 cm of soil of 320 t ha-' (HF), 240 t ha-' (AF), 200 t ha-' (DF), and 160 t ha-' in the top 11 cm of the LF. (6) Losses of K, Mg and Ca from litter bags were rapid while N and P were conserved; Na concentration increased in mixed leaves. There was evidence of the fauna increasing mineral losses from the leaves. Accession-standing crop quotients for elements confirmed the rapid flux of K and Mg at all sites; Ca had the highest quotient in the AF,