| dc.description.abstracteng | Rainforest conversion to agricultural plantations such as rubber and oil palm in Indonesia is increasing in the last decades. In this thesis, I investigated effects of rainforest conversion to rubber and oil palm plantations in Jambi, Sumatra, Indonesia. The study area serves as model region for investigating consequences of land-use changes on biodiversity, the channeling of energy through soil food webs and changes in trophic niches of one dominant group of soil mesofauna, Collembola. Collembola are among the most abundant arthropods inhabiting the belowground system sensitively responding to changes in vegetation and soil conditions.
In Chapter 2, consequences of the conversion of rainforest into plantations on the channelling of energy through soil food webs was investigated by using neutral lipid fatty acid analysis from six dominant soil fauna taxa. Rainforest conversion changed the biomarker FA composition of soil fauna at the community level. Conversion of rainforest into oil palm plantations enhanced the plant energy channel and reduced the bacterial energy channel. The changes in energy distribution within soil food webs may have significant implications for the functioning of tropical ecosystems and their response to environmental changes.
In Chapter 3, I investigated effects of rainforest conversion on the density, species richness, functional and community composition of soil and litter Collembola. Land-use change negatively affected Collembola communities in the litter layer, but the impact was less pronounced in the soil layer. Water content and pH were identified as important factors driving Collembola community composition. Several pantropical genera of Collembola (i.e., Isotomiella, Pseudosinella and Folsomides) dominated across land-use systems, reflecting their high environmental adaptability or efficient dispersal calling for studies on their ecology and genetic diversity. The decline in species richness and density of litter-dwelling Collembola with the conversion of rainforest into plantation systems calls for management practices mitigating negative effects of the deterioration of the litter layer in rubber plantations, but even more in oil palm plantations. Specific traits, such as larger size, patterned or intensive pigmentation and number of ocelli may explain the adaptation of Collembola species to the environmental changes in particular to changes in soil water content and pH.
In Chapter 4, the effect of rainforest conversion on the trophic niche structure of Collembola was investigated using stable isotope analysis. Across Collembola species, ∆13C values (calibrated to litter) were highest in rainforest suggesting more pronounced processing of litter resources by microorganisms and consumption of these microorganisms by Collembola in this system. Lower ∆13C values, but high ∆13C variation in Collembola in oil palm plantations indicated that Collembola shifted towards herbivory and used more variable resources in this system. Small range in ∆15N values in Collembola species in monoculture plantations in comparison to rainforest indicated that conversion of rainforest into plantations is associated with simplification in the trophic structure of Collembola communities. Across the studied ecosystems, atmobiotic species occupied the lowest, whereas euedaphic Collembola species occupied the highest trophic position, resembling patterns in temperate forests. A dominant species of the euedaphic life form and of high trophic position (Pseudosinella sp.1) was found in high abundance across rainforest and plantations suggesting that this species is best adapted to the studied land-use changes. Euedaphic species generally appear to be better adapted to cope with seasonal fluctuations than other life forms.
Additionally, in Chapter 5, I investigated seasonal fluctuations of Collembola density and community composition in rainforest and plantation systems. Collembola density in the litter layer, was at a maximum at the beginning of the wet season. Euedaphic and hemiedaphic species, living in the lower litter layers and soil, fluctuated less with season than epedaphic and atmobiotic species, living in upper litter layers. Differences in community composition among land-use systems were most pronounced at the beginning of the dry season (June). Collembola community composition changed with season in all land-use systems, with the differences being more pronounced in the litter than in the soil layer. In line with the results from Chapter 3, water content and pH were identified as important factors driving Collembola community composition across seasons.
Overall, rainforest conversion to rubber and oil palm have negative impacts on soil and litter Collembola biodiversity, alter the trophic structure of Collembola communities and the channeling of energy through soil food webs. To reduce the negative impacts of rainforest conversion into plantation systems as revealed in this thesis, improved management of agricultural plantations is needed. | de |