Environmental change and peatland forest dynamics in the Lake Sentarum area, West Kalimantan, Indonesia

Abstract

Four short pollen and charcoal records from sites within and around Lake Pemerak on the margins of the Danau (Lake) Sentarum National Park in inland West Kalimantan, supported by modern surface samples from the Reserve, provide a partial picture of lowland equatorial vegetation and environments over at least the last 40 000 years. They demonstrate general stability in the distribution of wetland and ombrotrophic (or raised) peatlands through the recorded period with dominance throughout of peatland and swamp forest. However, there was marked variation in sediment accumulation rates and in the floristic composition of the vegetation. The period prior to the last glacial maximum appears to have been the time of most active peatland growth and contrasts with the perception, from previous studies on largely coastal and subcoastal peatlands in Indonesia, that the Holocene was the time of major tropical peat accumulation. A general increase in charcoal, just prior to about 30 000 years ago, suggests that burning became more frequent, and is attributed to initial human impact rather than climate change. The subsequent latest Pleistocene period, embracing the Last Glacial Maximum, is marked by a peak in montane-submontane rainforest taxa, strongly indicating a substantial lowering of temperature. It appears that much of the Holocene is not recorded but recommencement of peat accumulation is evident within the last few thousand years. At the time of fieldwork access to the central part of the Lake Sentarum system was inhibited by strong El Niñ o drought conditions, but this area has the potential to provide a longer and more continuous history of environmental change for the region.

Drainage and land use impacts on changes in selected peat properties and peat degradation in West Kalimantan Province, Indonesia

“…Selected radio Carbon ages of tropical peats in Kalimantan and Peninsular Malaysia are so variable, spanning from 30 000 to hundreds of years (Anshari et al, 2001(Anshari et al, , 2004Page et al, 2004;Wüst and Bustin, 2004;Wüst et al, 2008). The radio Carbon analysis indicates that coastal peat in the Kapuas River basin is formed around 3000-4000 years BP (see Table 2).…”

“…Anshari et al (2004) reported that the age of peat from Danau Sentarum National Park in the upper Kapuas River is greater than 30 000 yrs BP (see Table 3). Further, a basal radio Carbon date of peat from Sebangau National Park is 20 000 yrs BP (Page et al, 2004).…”

“…More radio Carbon dates are required in order to detect the initiation of peats in this region. Also, it is important to note that peat formations are intermittently in several phases of accumulations and decays of organic matters (Anshari et al, 2004). The rates of peat accumulation in Kalimantan and Tasek Bera of Peninsular Malaysia are estimated to occur from 0.1 to 2.5 mm yr −1 (Wüst and Bustin, 2004;Page et al, 2004;Hope et al, 2005).…”

Forest contraction in north equatorial Southeast Asia during the Last Glacial Period

“…In addition, model results for the region greatly vary, with some indicating that a broad continuous lowland tropical rainforest was maintained and others suggesting savanna over major portions of Sundaland during the LGM (6,7). Surprisingly, there are no records from peninsular Malaysia and, in places where LGM sediments with suitable proxies are recovered, they may be compromised by biases such as riparian gallery forest vegetation and wind-blown tree pollen dominating riverine and offshore deposits (6,8,11,12), or lowland swamp regions being biased toward indicating wetter conditions (13). Hence, even the general distribution of LGM vegetation is disputed.…”

Modern humans in Sarawak, Malaysian Borneo, during Oxygen Isotope Stage 3: palaeoenvironmental evidence from the Great Cave of Niah

“…Pollen diagrams from Lake Sentarum and Setia Alam in west-central and south-central Borneo (Anshari et al, 2004;Kershaw et al, 2001) provide evidence for tropical rainforest during the Late Glacial Maximum (LGM) in those areas. It is suspected, however, that during these times dry dipterocarp woodland and savannah expanded into regions now occupied by humid lowland rainforest (Hope et al, 2004;Bird et al, 2005).…”