Long-term dynamics of tropical rainforests, climate, fire, human impact and land-use change in Indonesia
A focus on the montane rainforests in Central Sulawesi and peat-swamp rainforests in Sumatra
von Siria Biagioni
Datum der mündl. Prüfung:2015-05-11
Erschienen:2016-05-09
Betreuer:Prof. Dr. Hermann Behling
Gutachter:Prof. Dr. Hermann Behling
Gutachter:Prof. Dr. Erwin Bergmeier
Gutachter:Dr. Dietrich Hertel
Zum Verlinken/Zitieren:
http://dx.doi.org/10.53846/goediss-5639
Dateien
Name:Biagioni_PhD_thesis.pdf
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Description:Siria Biagioni PhD dissertation
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Zusammenfassung
Englisch
The research conducted and compiled in this thesis contributes to the knowledge of the long-term vegetation, climate and fire dynamics as well as human impact on montane and peat-swamp rainforests of Indonesia. We applied multi-proxy palaeoecological methods to three sediment/peat cores taken from Lake Kalimpaa and Lake Lindu in Central Sulawesi and from Air Hitam peatland in Jambi Province, Sumatra. The Lake Kalimpaa record is the first archive from Central Sulawesi providing information on palaeovegetation dynamics under the background of reconstructed palaeoenvironmental and palaeorainfall conditions throughout the past ca. 1500 years. The palaeovegetation as reconstructed from the palynological analysis reveals that around Lake Kalimpaa the Fagaceae family dominates the entire recorded period, as it still does today. Two disturbance events (ca. AD 1090-1190 and ca. AD 1450-1620) occurred in the catchment area of Lake Kalimpaa as reconstructed from sediment grain size and geochemical analyses. Comparison with fire frequency derived from macro-charcoal analysis indicates that these events were caused by forest fires. The regional correlation of these events with periods of drought registered elsewhere in Sulawesi and in Java suggests that centennial-scale increases in fire frequencies at Lake Kalimpaa were consequences of the vegetation being more prone to fire, probably due to more frequent and/or longer El Niño events. Despite that, Fagaceae did not decrease, indicating resilience towards droughts of at least one species of the family. However, palynological diversity values indicate that within-landscape diversity (Whittaker’s gamma diversity) decreased when fires increased. Palynological rate of change and compositional turnover indicate that vegetation communities were more resilient to fire disturbance during periods of average high rainfall. Palynological, charcoal and diatom reconstructions of the Lake Lindu core reveal that humans have modified the landscape at the Lindu plain for at least 1000 years. Evidence of frequent burning and possible shifting cultivation from an earlier phase from ca. AD 1000 to 1200 might be related to the metal age population which erected the megaliths in the province of Central Sulawesi. From ca. AD 1200-1700 decreases of macro-charcoal concentrations and pioneer vegetation indicators show that the use of the landscape of the Lindu plain had become more permanent. Due to the little research conducted so far on the megalithic culture of Central Sulawesi, it remains uncertain whether the architects of such a cultural change were the megalith people or a different ethnic group. A phase of forest recovery from ca. AD 1730 to 1910 correlated with a decrease in human activities in the valley, which historical reports describe as mostly limited to fishing and cattle grazing. These results suggest, that when human pressure on the landscape decreases as a consequence of different strategies of subsistence, the montane ecosystems possess a great capacity of recovery and fagaceous forest communities can expand within a relatively rapid time scale. The multi-proxy palaeoenvironmental and palynological results from the Jaw SPT core in the Air Hitam inland peat in central Sumatra show a picture of a highly dynamic system. Since the beginning of peat accumulation around 7800 years ago net balance accumulation exceeded degradation, and the system remained a carbon sink. At first the peatland in Air Hitam was fed by fluvial run-off and the vegetation gradually changed from mixed Dipterocarpaceae swamp to marshy swamp communities dominated by Durio trees around 5300 years ago. A marked change in the vegetation community’s composition occurred at the beginning of the late Holocene about 4500 years ago. A pole forest established, with Pandanus thickets colonizing the area as the dome developed into a rainfall-fed ombrogenous system. At the same time, macro-charcoal peak detection analysis reveals that fire frequency increased, possibly a consequence of the ENSO-onset. Peat accumulation rates and hence carbon storage in the dome of the Air Hitam was considerable in the past. Higher rates of peat/carbon accumulation were found to correlate with Pandanus expansion under ombrotrophic settings. The testate amoebae assemblage indicates that the phases of ombrogenous Pandanus-pole forest were characterized by lower water table fluctuations. Despite the lower biomass input the peat accumulation rate was in average higher than during the mixed-swamp community phases. The correlation between high peat accumulation and relatively drier phases linked to ENSO makes the area of Air Hitam potentially one of the most effective carbon sequestering ombrotrophic peatlands in the view of future climate scenarios. The results of charcoal analysis in montane (Lake Kalimpaa) and peat-swamp (Air Hitam) ecosystems show that although rare, wildfires did occur in the past in Central Sulawesi and Sumatra. The regime of fire, in particular the frequency, was found to correlate with regional scale drought episodes in Central Sulawesi. Both, fire frequency and magnitude of events, increased at Air Hitam in correlation with the increase in the number of El Niño events in the late Holocene. These results indicate that fire regime of montane ecosystems in Central Sulawesi and peat-swamp forests in Jambi can change in the long-term following changes in rainfall patterns and ENSO variability. However, our results indicate that the effects of fire and droughts on the carbon storage functions of the two systems under study might not have been marked. In particular, Fagaceae representation around Lake Kalimpaa was not affected by increases of fires caused by drought and carbon accumulation capacity of the ombrotrophic-Pandanus dominated ecosystems in Air Hitam did not change (but rather increased) when frequency and magnitude of fires increased. These results suggest that under natural conditions, fires occur in these ecosystems, but the effects on their carbon storage functions in time can be relatively low. A strong acceleration of disturbance driven by human activities is underlined by the results in both the regions under study for the past decades. The overall results of this research highlight that the pressure exerted over millennia on montane and peat-swamp rainforests in Indonesia has been of a different magnitude than the modern anthropogenically driven changes. The results from the research compiled in this thesis highlight the value of using a multi-proxy approach in order to better understand dynamics and functions of tropical ecosystems and to identify the most important drivers of long-term changes.
Keywords: palaeoecology; palynology; pollen; spores; vegetation history; climate change; charcoal; fire; rainforests; Indonesia; Sumatra; Sulawesi; tropical peatlands; montane rainforests; megaliths