A S
You also mentioned the relationship of Lake Towuti and the Wallace Line when you told us that you were researching some specific “climate refugia” in the area. Can you tell us about these refugia in relation to Wallace’s research on evolution, speciation, and biogeography? It would also be interesting to learn more about the term “climate refugium” itself.

S W
In a paper that I published recently,³ I concluded that elevation played an important role in determining the ecological manifestation of climate change in Indonesia. Based on two sets of climate and environmental proxy data from Lake Towuti and another lake located at a higher elevation (Lake Matano), there was a substantial difference in terms of rainfall and plant ecosystems surrounding the two lakes in the past. During the last ice age, when the climate in central Indonesia was generally drier and more seasonal, higher-elevation regions such as Lake Matano’s catchment were wetter and had a higher percentage of rainforest taxa compared to lower elevation regions.
   
Since those high-elevation regions served as a home for rainforests amidst grassland expansion due to the drying climate, we may call them “climate refugia.” When the climate became more favorable (i.e. wetter), the rainforests might have expanded, encroaching on lower-elevation regions at the expense of the grasslands. Given that there are multiple highlands in Sulawesi, as well as other Indonesian islands, there might have been multiple “climate refugia” during dry periods.
   
Our data point to several cycles of drying and wetting in the past, implying that a series of rainforest expansion and contraction cycles might have occurred around the refugia. The expansion of rainforests from nearby highlands could have played an important role in the evolution of plants. Different refugial peaks might have contained distinct plant species as they underwent different climatic and biological histories. Thus, when expansion occurred during wetter periods, and different yet still-related species intermingled, new plant species might have been produced. We thus hypothesize that the presence of climate refugia in Sulawesi played a crucial role in maintaining the high biodiversity in the region.

A S
We imagine that in 800,000 years there have been quite significant changes in Sulawesi and the ancient lake you are studying. Yet, we wonder if the more recent changes to Indonesia’s rainforests, biodiversity, and land-use are even more extreme, but on a much shorter timescale. To change the direction of our thought for a moment, what does the future look like given the current land-use practices in Indonesia? In another 100,000 years, what might one find if the Towuti Drilling Project occurred again at the same site?

S W
If you look at the landscape around Lake Towuti now, you will see patches of barren, cleared land. It isn’t difficult to pinpoint what the culprit was. Almost every day, and peaking on the weekends, you see smoke coming from the hills bordering the lake. Farmers want to clear the land to cultivate pepper, currently a very profitable crop, so they ignite the fires, essentially destroying all the trees in certain parcels of land. There are also illegal loggers who fell the trees around the lake. The loggers are slightly more environmentally friendly than the pepper farmers since they only selectively take down the big trees. These two activities are certainly worrying, given the potential environmental impacts on the lake ecosystem. It is also saddening given that Lake Towuti is actually a conservation area under the jurisdiction of the Ministry of Environment and Forestry.
   
If one were to drill the lake sediment at the same site 100,000 years from now, one might encounter cores that have much higher sedimentation rates during the Anthropocene than the Holocene because of the increase in erosion. There is also a possibility that by then Lake Towuti will be much shallower than today. Chemical fertilizers that are used in pepper farming may also increase the amount of nitrates and phosphates, thus increasing the biomass of phytoplankton and algae. As a result, sediment cores extracted in the future may have a substantially higher percentage of organic matter than what we found in 2015. Finally, we would see plenty of trash that humans threw in or near the lake. Plastic bags, bottles, and other relatively non-degradable materials could be easily seen in future sediment cores.