Over the last decades, the lowlands of Jambi province in Sumatra (Indonesia) have undergone a major transformation from forests towards a crop-dominated landscape of rubber and oil palm plantations. EFForTS is a Collaborative Research Centre 990 funded by the German Research Foundation (DFG) that investigates the ecological and socio-economic effects of such transformation based on research carried out in the Bukit Duabelas and Hutan Harapan area in Jambi province focusing on smallholder systems (Drescher et al. 2015). In the EFForTS project, more than 160 researchers from the University of Göttingen in Germany and the Indonesian universities IPB (Bogor Agricultural University), UNTAD (Tadulako University) and UNJA (Jambi University) work in close cooperation, representing a wide range of disciplines including ecology, forestry, agriculture, remote sensing, economics, human geography, and cultural anthropology.
The first six years of research of the CRC 990 revealed complex trade-offs between ecological and socio-economic effects. Here we summarize the key findings.
When rainforests are being converted to commercial land-use systems such as jungle rubber (a local agroforestry system where rubber trees are planted in a logged-over forest), or rubber, or oil palm plantations, carbon is lost. In each of these examples (jungle rubber, rubber or oil palm), carbon losses resulted as follows: 116 Mg C ha-1 (tonnes of carbon per hectare), 159 Mg C ha-1, and 174 Mg C ha-1. Most of the carbon loss originated from above-ground carbon pools and represented a loss of 41%, 56% and 61% in carbon respectively (Guillaume et al. 2018; Fig. 1B). Oil palm cultivation resulted in the highest carbon storage losses, but due to the high oil palm yield it was actually the most efficient land use, i.e. oil palm had the highest yield per unit of carbon storage loss (Guillaume et al. 2018; Fig. 1A; see also Dislich et al. 2017). Ecosystem water cycling was also affected by forest transformation. Compared to selectively logged rainforests, plant water use (‘transpiration’) was 12% lower in jungle rubber agroforests, 43% lower in rubber monocultures and 19% lower in smallholder oil palm plantations. In commercial, intensively managed oil palm plantations, transpiration was 40% higher than in forests (Röll et al. 2019). Total water loss from commercial oil palm plantations (‘evapotranspiration’), as assessed by eddy covariance measurements, were also substantial (Meijide et al. 2017). Soil structure degradation and associated erosion after forest conversion (Guillaume et al. 2015, 2016) strongly reduced soil water infiltration and increased surface run-off, more so in oil palm plantations than in rubber plantations (Tarigan et al. 2018). Together with high water losses from (evapo)transpiration, this can lead to additional reductions of available water and even occasional water scarcity in oil palm dominated landscapes (Merten et al. 2016). Converting forest to plantation also affected the local climate. The air inside oil palm and rubber monocultures was warmer (by about 2.2°C) and drier (about 12% less relative humidity) than inside forests, and forest conversion amplified the diurnal range of all microclimatic variables studied (Meijide et al. 2018). Remote sensing data further indicated a local warming effect after forest conversion (Sabajo et al. 2017), with land surface temperature differences of up to 10°C between natural forest and land after clear-cut (Sabajo et al. 2017). The analysis of the land surface temperature trend of the past 16 years indicated that the average daytime surface temperature in Jambi province increased by 1.1°C exceeding the effects of climate warming (Sabajo et al. 2017).
Jambi province has lost most of its lowland rainforests since selective logging and conversion to other land-uses intensified in the 1970s. The period between 1990 and 2000 was characterised by particularly high rates of deforestation and land-use change (Clough et al. 2016). Today most of the province consists of monoculture plantations. In terms of area covered, rubber and oil palm are the two most important crops in Jambi, with the oil palm area expanding particularly fast.
Our field studies showed that different indicators of naturalness and species richness were highest in the forest, and successively decreased in jungle rubber, rubber plantation and oil palm plantation (Fig. 1C, D). A comprehensive analysis of the biodiversity of different taxonomic and functional groups, including plants, bacteria, fungi, protists, soil and canopy invertebrates as well as vertebrates, documented an overall strong decrease in local diversity in oil palm and rubber plantations as compared to rainforest (Rembold et al. unpubl. data). However, at the plot scale, birds and bats showed no response to land-use change and soil bacteria and archaea (Schneider et al. 2015) as well as certain protist groups (Schulz et al. 2019) had higher diversity in rubber and oil palm plantations than in forest.
Besides strong negative effects on local diversity, land-use intensification also affected the composition of biological communities. For instance, oil palm and rubber forests differed markedly from those of rainforest, while jungle rubber agroforests shared more similarities with forests and were characterised by a relative high proportion of forest species (Prabowo et al. 2016, Rembold et al. 2017, Drescher et al. unpubl. data). Another important trend was the increased abundance and dominance of invasive alien species in the monoculture plantations (Rembold et al. 2017, Drescher et al. unpubl. data).
Important ecological functions including tree biomass, litter decomposition, root health, microbial activity and biomass were significantly reduced in monoculture plantations (Clough et al. 2016, Sahner et al. 2015). Similarly, nutrient-leaching fluxes were higher in oil palm plantations. While the harvested biomass increased from forest to jungle rubber to monoculture plantations, total biomass shows the opposite pattern (Kotowska et al. 2015, Clough et al. 2016). Multidisciplinary research also showed up to 51% reduction in the flux of energy to higher trophic levels of litter food webs in monoculture plantations than in rainforest, indicating strongly reduced predator control of prey species (Barnes et al. 2014). However, the flux of energy into detritivore animal species (i.e. those that feed on dead organic matter) was strongly increased in monoculture plantations, mainly due to earthworms benefitting from higher pH in plantations (Potapov et al. 2019).
Rubber and oil palm are clearly the two most important income sources for the population in rural Jambi. This holds true for farm households and also for non-farm households that often find employment on rubber and oil palm plantations (Euler et al. 2016, Bou Dib et al. 2018a). While rubber has been a traditional crop in the region for more than 100 years, oil palm was only introduced in the 1980s and has expanded rapidly since then (Gatto et al. 2017). Both crops are grown on large company plantations as well as by smallholder farmers. Smallholder oil palm cultivation in Jambi started as a result of the transmigration program of the Indonesian government in the late 1980s. This program moved people who had no land from densely populated areas to less populous areas of the country. Initially, smallholders produced oil palm under contract with large companies. However, nowadays most of the smallholder oil palm cultivation takes place independently, without company contracts. It is estimated that smallholders currently produce around 40% of the total palm oil in Indonesia (Byerlee et al. 2017, Euler et al. 2017).
Comparing the economic effects of rubber and oil palm in the smallholder sector, rubber led to higher profits per unit area than oil palm when a lot of family labour is used (Fig. 1E). However, rubber was much more labour-intensive than oil palm, so that the return per unit labour cost was higher in oil palm cultivation (Euler et al. 2017; Fig. 1F). Our representative data from smallholder farm households in Jambi showed that oil palm was more profitable than rubber and that households that cultivated oil palm had higher incomes and enjoyed higher living standards than households that had not adopted the oil palm crop (Krishna et al. 2017). These economic gains from oil palm cultivation were also the main reason for the rapid expansion of the oil palm area in the small farm sector (Kubitza et al. 2018).
Rural non-farm households benefited from the shift from forest to monoculture rubber and oil palm plantations through additional employment opportunities (Bou Dib et al. 2018a). The associated gains in employment incomes were important from a social perspective, because non-farm households typically belong to the poorest population segments in rural Jambi. Our data showed that poverty rates are close to 20% in villages where little rubber and oil palm were cultivated. In villages where rubber was the dominant land-use type, the average poverty rate was around 14%; whereas in villages where oil palm was the dominant land-use type, the poverty rate was only around 8% (Bou Dib et al. 2018b).
Our qualitative case studies showed that the expansion of oil palm plantations and the simultaneous expansion of protected areas have fostered tensions over land (Hein et al. 2015; Hein 2018, Kunz et al. 2017). The research results demonstrated that land tenure regulations are complex. We found that regulations, which were added over time by various political authorities at different levels of governance, to customary laws created a situation of legal pluralism (Kunz et al. 2017). Recent territorial conflicts mirror the contradictory interests of different governmental organisations, transnational actors, and local people, influenced by conservation-oriented and development-oriented groups of the society (Hein et al. 2018, Hein 2019). This also resulted in smallholders being deprived of access to land due to the allocation of concession areas for development or conservation purposes by the state, often lacking secure title deeds for sustaining their livelihoods (Beckert 2017).
The presence of native trees within oil palm plantations may have a positive impact on biodiversity, but may also be associated with economic losses. The trade-off between ecological benefits and economic losses, however, is least pronounced in intensively managed plantations, where an increase in tree density had the largest positive effect on the diversity of birds and the fewest repercussions on farmers’ revenues (Teuscher et al. 2015). To evaluate the ecological and socio-economic impact of tree planting in oil palm monoculture, the EFForTS project established a biodiversity enrichment experiment in 2013 (Teuscher et al. 2016). Six multi-purpose native tree species were planted, oil palms were partly thinned, and fertilizers and herbicides no longer applied.
Survival rates and tree height varied widely among species. Shortly after planting, beneficial effects on bird and invertebrate communities could already be observed (Teuscher et al. 2016) with the number of planted tree species increasing the structural complexity of the vegetation and thereby presumably also other ecosystem functions (Zemp et al. 2019a). Notably, the yield loss associated with oil palm removal was compensated by per-palm yield gain, which was attributed to oil palm thinning, whereas tree planting had no effect on yield (Gérard et al. 2017). This positive effect, however, was restricted to the first years after planting. Trees grew less well in the proximity of oil palms, suggesting a trade-off between tree growth and palm oil production (Zemp et al. 2019b).
In order to support tree planting in oil palm plantations, smallholder oil palm farmers were identified as key actors due to their growing importance in the oil palm sector in Indonesia. Missing knowledge about how to manage trees in oil palm plantations and missing markets for high quality tree saplings appeared to hinder tree planting. These barriers can be overcome with the help of information and seedling provision. Both of these interventions increase the number of trees planted per hectare in smallholder plantations (Romero et al. 2019).
The transformation of the lowland forests of Jambi province towards a crop-dominated landscape had pronounced effects on ecological and socio-economic functions. While the environmental effects were predominantly negative, the cultivation of rubber and especially oil palm contributed to higher income, poverty reduction, and improved living standards among smallholder farmers and rural workers although at times this contributed to increased conflict over land ownership. These trade-offs between the ecological and socio-economic effects need to be accounted for in sound policies for more sustainable land use. Management measures, such as enriching monoculture plantations with other tree species, are able to mitigate some of the negative effects and deserve further study.