Benthic macroinvertebrates and logging activities

Abstract

At the beginning of the 21 century, the conservation of biodiversity and the sustainable use of natural resources remains a matter of concern. Within this framework, the aim of this research was to study the effects of logging activities on ecological water quality indicators in a tropical forest. The study was undertaken at both local (species/habitat) and landscape (watershed) scales. The study took place on Borneo Island, in East Kalimantan province (Indonesia), in a state-owned timber concession, on an area of 85 km2. In order to study the impact of logging activities at landscape scale, five satellites images (1991, 1997, 1999, 2000 and 2001) were examined. The ecological water quality was evaluate by a biological and a habitat assessment, which were performed at each stream reach. The biological assessment constituted in collected benthic macroinvertebrates. This protocol was conducted at 23 sampling sites on headwater streams in order to compare the impacts of logging in logged area versus unlogged area. Logged area were grouped by the time interval after logging. We examined several groups: recently logged (during logging and until 6 months after logging), 1 to 3 years after logging and, 4 to 5 years after logging and relogged for a second time. Two field seasons occurred in June-August 2000 and April-May 2001. During this eight months time interval, most of the timber concession was relogged for a second time, as a result of the decentralisation process at government level. The research took four years and the following main results have been obtained. Logging activities at landscape scale were quantified by the total length of logging roads. This underlined the intensification of the logging activities from one satellite image to the other over the time (from 1991 to 2001). Vegetation classification and vegetation index (NDVI) could not be used to assessing the impact of logging activities on forest quality because of the homogeneous forest cover in the study site (no visible patches). Benthic macroinvertebrates and environmental variables were considered an ideal tool to assess the ecological water quality in the study site. Macroinvertebrates richness was high with 115 taxa mainly identified at family and sub-family level (genera for Ephemeroptera), but abundance was low (mean density of 770 individuals per square meter, ranging from 86 to 2130). Multivariate analysis highlighted that the size of the streams and the impact of logging activities played an important role in ordinating the samples. A co-inertia analysis demonstrated that benthic macroinvertebrates and environmental variables were found to be strongly related to each others. The main results indicated that macroinvertebrate density, richness, diversity, composition and functional feeding organisation responded to logging activities. During and six months after logging, macroinvertebrate density was higher and diversity indices were lower compared to the reference samples (unlogged situation). One to three years after logging were found to be the most disturbed situation, indicated, among other things, by an even lower diversity indices. Environmental variables responded to logging activities by: an increase in opening, water temperature, amount in fine sediment and flow velocity and by a decrease in Fine Particulate Organic Matter (FPOM). The stream ecosystems seemed to recover 4 to 5 years after logging in absence of ongoing activities, density and diversity seemed similar but benthic macroinvertebrate composition is different compared to reference unlogged situation. Among the 115 taxa identified during the study, several were indicator taxa, meaning that they characterised the impact of logging activities at a given time. Indicator taxa were grouped in five categories: open canopy taxa (Platybaetis, Lepidoptera, Hydropsychinae); sensitive taxa (e.g. Caenodes, Limonidae, Potamanthus, Perlidae, Philopotamidae); pulse taxa (e.g. Psephenidae, Jubabaetis, Platybaetis, Megaloptera, Glossossomatidae) ; recovery taxa (e.g. Labiobaetis, Helicopsychidae, Platystictidae) and adaptive taxa (Diplectroninae, Simuliidae, Isca). A Tropical Stream Concept was proposed to take into account the paucity of shredders collected in the headwater catchment streams. The higher decomposition rate and terrestrial shredders provides the Fine Particulate Organic Matter as direct input from the washing out of the catchment during rainy events. In summary, macroinvertebrates can be considered excellent indicators, which were successfully used in this tropical environment for both objectives: they assessed biodiversity as an element of forest sustainability and they assessed disturbances due to logging activities, with the advantage to be indicative of recent and past events. Further research is proposed to test the identified indicator taxa to other regions in Borneo, to valid them and to prepare a simplified key to be used by local institutions as a tool for monitoring ecological water quality.