• Once covered in vast tropical forests, East Kalimantan, in the Indonesian half of Borneo Island, is today the most intensively mined province in Indonesia.
• Surface mining for coal has left behind vast expanses of barren land across the province.
• Under Indonesian law, mining companies are responsible for rehabilitating their mining concessions.
• In this analysis, based on field work in mining sites in East Kalimantan, restoration ecologists David Woodbury (School of the Environment, The Forest School, Yale University ) and Arbainsyah (Environmental Leadership & Training Initiative, Tropenbos Indonesia) argue the rehabilitation of coal mines is far more difficult, and likely far less effective, than environmentalists, mining companies and policy makers might hope.

Sitting cross-legged on a rough, wood plank floor, Jaidun is clad in the light-blue, button-up shirt that identifies the rehabilitation workers at PT Singlurus Pratama, a coal-mining company in East Kalimantan province, on the Indonesian portion of the island of Borneo. With a cigarette in one hand and a ball of rice in the other, he explains how he and his coworkers have restored the forest surrounding the platform where he sits.

First, they trucked in topsoil to cover the regraded and hard-packed rubble that filled the spent coal pits. Then they planted two tree species, acacia (Acacia mangium) and sengon (Paraserianthes falcataria), and filled a small pit that remained from mining with water and stocked it with fish. Once the trees grew large enough to cast shade, they built the platform to have a quiet, green place to eat lunch within the heart of the coal mine area. Jaidun said he was happy to see birds return to the new trees around the pond.

Eating my own rice and sweating in the midday heat, I listened to Jaidun’s story of landscape transformation with a mixture of guarded optimism and resignation. I was there as a restoration ecology researcher from Yale University with my colleague, Arbainsyah, a botanist from the Tropenbos Indonesia Program. Together we were leading a project to evaluate the landscape rehabilitation strategy Jaidun had described.

In East Kalimantan, the most intensively mined province in Indonesia, mine pits expand across more than 5 million hectares (12 million acres) of land already zoned for coal concessions. The barren pits hamstring local economies because they are not viable for many local livelihood practices, like rubber plantations or agriculture.

Under Indonesian law, mining companies are obligated to restore the land they have torn open to extract coal. In reality, this responsibility is poorly enforced and often ignored, resulting in vast expanses of unproductive and polluted land that endangers local communities. According to activists, mining companies have left behind more than 87,000 hectares (215,000 acres) of abandoned mine pits in the province.

Unfortunately, even when companies do work to meet their obligations, the rehabilitation law itself is also problematic. The law states that coal companies must restore the “original condition” of the landscape — an unrealistic target that even in the best-case scenarios is not supported by current science on mine rehabilitation. By suggesting that restoring the “original condition” is possible, the law clouds the extent and scale of degradation left behind after surface mining. It misrepresents what is feasible through ecological rehabilitation. After studying former mine sites in East Kalimantan, Arbainsyah and I came to the grim conclusion that coal mine rehabilitation is not as simple, nor perhaps as successful, as environmentalists, coal mining companies or policymakers hope.

Hazards of coal mining in East Kalimantan

East Kalimantan is home to one of the world’s most biodiverse rainforests, including charismatic species of hornbills and orangutan that only exist on the island. These forests, called “lowland mixed dipterocarp forests” after the family of trees that dominate the canopy, have more plant diversity than almost any other place on Earth. East Kalimantan is also the greatest coal-producing province in Indonesia, the second-largest coal exporter in the world. Predictably, deforestation from mining poses a significant threat to the region’s unique biodiversity and the health and quality of life of local communities.

Coal extraction here happens by a process called surface mining, in which all vegetation, soil, and rock are removed by heavy equipment and explosives to expose coal seams. Once the mining process is over, vast, barren and polluted pits are left behind, leading to erosion and polluted runoff, affecting downstream fish populations and drinking water. These mine pits often fill up with water, which poses a safety hazard for locals when unstable banks collapse, trapping swimmers. At least 39 people, many of them children, have drowned in the last eight years in abandoned mine pits.

The widely accepted solution to address surface mining’s environmental dangers is ecological rehabilitation, the process of landscape transformation described by Jaidun. Indonesian law dictates that coal companies must set aside resources to pay for rehabilitation before mining. Companies are then required to conduct progressive rehabilitation in mining concession areas where operations are complete.

However, the law’s language can lead to multiple interpretations and confusion. The directive requiring mining companies to rehabilitate the land to “rona awal” or the “original condition,” often causes confusion among rehabilitation workers and local community members about what this terminology means.

Historically, most of East Kalimantan was forested, but today very little of that primary forest remains. Mining happens on various landscapes, including selectively logged forest, grasslands, and industrial timber plantations. This begs the question: must the mining companies return the land to the state before mining or return it to the native forest? In some cases, the land is classified for conversion to industrial timber plantations after mining, so what is the use in returning abandoned mines to their “original condition” first? And when the land is not classified for conversion to plantations, the law states that mining companies should negotiate with local stakeholders to determine the target of rehabilitation. What if local stakeholders do not want to restore the original condition?

However, from an ecological perspective, the biggest issue with the language of the law is that it assumes rehabilitating abandoned coal mines to their “original condition” is even possible.

Land degradation from surface mining

To reach PT Singlurus Pratama’s rehabilitation sites, which cover more than 100 hectares (250 acres), we had to drive through the heart of the mining operation. We made this trek every day for several months, and the process was always the same. A deep sinking feeling entered my gut at the gate, where we attached a flag and flashing yellow light to our truck and switched on the radio to a static crackle and air traffic control-like voices coming from heavy equipment operators inside the mine. Once the gate opened, exposed red earth stretched to the periphery of our vision ahead. After a minute, we reached a precipice where an open pit lay before us. Excavators worked sequentially to uncover and shovel coal into dump trucks that waited to carry it away for processing. Later, the coal would be carried again by dump trucks to the endless parade of barges that cross the passage from Borneo to Java, where, finally, the coal is used to fuel power plants or loaded onto much larger ships bound for distant ports in China.

The first time we made the trip, we pulled up to the edge of the pit and looked out across the expanse of environmental degradation. An alien landscape lay before us: bare, bright red earth with no vegetation and the occasional crater carved into the hillsides. When we drove further, the mine’s lifeless expanse spread in front of us as far as we could see. We splashed through large puddles colored saffron from acid mine drainage. High mounds of red soil, piled like landfills, with broken tree trunks and large rocks scattered throughout, marked by signs that read “stock topsoil,” were waiting to be dumped back into the pit once the coal resource was exhausted.

Forest recovery after this level of damage is prolonged, and humans need to facilitate forest regrowth to shorten the time frame. This “ecological rehabilitation” or “restoration” comprises a collection of management strategies to kick-start or accelerate the process of ecosystem recovery. And these interventions come at a high cost with mixed results.

The practice of ecological mine rehabilitation is derived from the study of how ecosystems recover after they are damaged, known as ecological succession. These practices are also informed by restoration ecology, the study of what interventions can be made to speed up the process of ecosystem recovery.

Ecological recovery starts after natural or human-made events cause plants to die. Ecologists call these events “disturbances.” In East Kalimantan, common natural disturbances include strong winds, periodic drought, and occasionally fire. Often, after these types of natural disturbances, ecosystem recovery can happen without any restoration interventions. New and surviving trees fill in the gaps that are left by the disturbance. These trees grow taller and broader, and the composition of species becomes more diverse with time.

However, in relatively recent ecological history, humans have become the leading cause of disturbance in tropical forests like those that blanket Borneo. Human-caused disturbances are often more destructive and take longer to recover from than natural ones. As a result, they can necessitate restoration management interventions like tree planting or invasive species removal. Coal surface mining, where miners remove all vegetation, soil and underlying rock across dozens or hundreds of hectares, is particularly destructive and requires intensive restoration management interventions to facilitate ecosystem recovery.

Conventional rehabilitation strategies

The primary challenge in coal mine rehabilitation is to repair the soil, which provides a place for vegetation to establish and forest trees to grow. It also holds water and supplies the nutrient building blocks needed to support plant growth. First, the soil needs stabilization with fast-growing plants such as grasses, sedges and vine-like spreading legumes often called “cover crops,” which prevent erosion and polluted runoff and can begin to replenish soil health. Soil damaged during mining has depleted levels of many nutrients, which are already limited in rainforest soils [1].

While current policy requires coal companies to respread the soil that they removed during mining, recovery of complex soil ecosystem components like invertebrates (bugs), microorganisms (bacteria and fungi) and nutrients are necessary before the soil can support the growth of native forests. To ecologists in East Kalimantan, only the top 1-5 centimeters (0.5-2 inches) of native forest soil is topsoil, which is the soil profile section where most of the nutrients and biotic life exist. For many mining companies, topsoil has a very different definition. It includes the entire soil profile from the surface down to the bedrock meters below, meaning they dump back tons of earth with few nutrients, which is not a replacement for the thin but relatively rich slice of soil that ecologists identify as important.

The next step of the rehabilitation strategy at PT Singlurus Pratama and similar mining firms involves densely planting two exotic tree species, sengon and acacia, that grow well in degraded soil. Both the cover crops and the tree species planted are nitrogen fixers that help replenish the nitrogen in the soil. Together these planting steps form the conventional post-coal mine rehabilitation strategy across East Kalimantan used by the companies that do not shirk their responsibilities to rehabilitate abandoned sites.

In mined areas zoned for conversion to industrial plantations, this strategy works because the trees planted are the same trees that comprise the plantation.

When targeting the restoration of native forests, conventional wisdom suggests using the same strategy because acacia and sengon can grow on post-surface mined sites and start to improve growing conditions so that native species can grow around them. Dense grasses begin to recede as the plantation canopy grows, blocking the full sunlight that the grasses need to survive. Meanwhile, the native forest tree species that enter the site from surrounding forests are generally more tolerant of shade and can grow in the plantations’ understory [2], [3]. This strategy’s logic is that native trees will dominate the understory and eventually replace the plantation trees in the forest canopy, restoring the native forest. Past research shows that this strategy is useful for restoring simplified native forests in other highly degraded tropical landscapes [2]–[4]. Our research team sought to validate whether this strategy was also effective for coal mine rehabilitation in East Kalimantan by looking at different aged plantations to explain the trajectory of forest recovery occurring there.

We found that the tree plantations did have some positive impact on soil recovery but whether these plantations are on a trajectory toward the “original condition” was unclear [5]. The forest recovery Jaidun described from the platform is mostly absent of native species, with only sparsely spaced native seedlings that may die before they ever reach the canopy. The oldest plantations we looked at, already nine years old, had no resemblance to the surrounding native forest. And although acacia is still widely planted, it is classified as invasive in many degraded areas of East Kalimantan and it is unclear whether it will ever concede space to native forest vegetation [6].

The ‘original condition’

The differences between a plantation forest and a native forest are striking. Several weeks after eating lunch with Jaidun, Arbainsyah and I set out to establish plots in the native forest to compare them to the other plots we had established in the plantations. We led our research team on a small dirt track through a nine-year-old coal mine rehabilitation plantation where grasses, sedges and small shrubs dominated the understory. The ground was hard and dry and cracked from the heat. After five minutes following the trail, we neared a small stream that marked the plantation’s edge. A wall of vibrant green vegetation rose before us. We crossed the water on a slippery, barkless tree and passed through a small gap in the vegetated wall to enter the native forest.

Broad dark leaves replaced the grasses and sedges of the plantation understory, encroaching on the path and tickling our ankles. In seconds, the air became thick with moisture, and steam rose around us. I blinked as my eyes adjusted to the low light. Only 50 meters into the forest and the songs of hundreds of birds rang down from the canopy. The buzz of insects hung in the air. We pressed on into the enveloping environment following the track, at times pushing aside vines hanging from the tree crowns in the sky above us.

This forest dripping with life is the “original condition” of the landscape where mining occurred at PT Singlurus Pratama. Clearly, the plantations have a long way to go before they resemble the native forest.

Being realistic about coal mine rehabilitation

It is still too soon to know whether these exotic plantations will develop to become the lush native forests surrounding the mine or whether they will ultimately collapse because of degraded soils. What is certain is this recovery will be slow, and any resemblance to the forest that was cleared for mining unlikely for at least several hundred to possibly thousands of years.

It is possible to make even more intensive management interventions such as trucking in topsoil or using heavy commercial fertilizer applications to speed up ecosystem recovery further. However, these methods are too expensive to be economically viable in most mining contexts.

Our research group concluded that with the current state of technology, restoring forests on abandoned coal mines is unrealistic in any tangible time frame, even in the best-case scenarios. In the reported cases of “successful” rehabilitation, the restored ecosystem is a highly simplified version of what existed before mining [7]–[9].

Current policy on restoration within the Indonesian forest estate is inherently flawed because current science indicates that truly restoring a mining site to its original condition is an impossible task, especially if the target is restoring the native forest [5], [9], [10]. Consequently, the law sets an unreachable target for companies while also promoting the unrealistic idea that the environmental damages wrought by mining can be fully reversed.

Considering these current ecological realities, if slowing the spread of landscapes degraded by mining is a priority for policymakers in East Kalimantan, then coal mining should be limited where possible. And where mining must continue, policy changes that allow coal companies to target achievable restoration outcomes and restore value and functionality to the landscape will be beneficial [9], [11]. These policy changes should prioritize restoration that prevents polluted runoff, drownings in abandoned pits, unproductive expanses of land, and mining in native forests.

A way forward

Ongoing explorative research conducted by the Indonesian environment ministry’s conservation R&D unit (Balitek KSDA) and others includes native species trials to determine which native plants grow best on abandoned mine sites, whether mine pits can become fishponds after remediation, or whether agroforestry systems (the inclusion of trees in agricultural systems) might be viable alternative land uses for abandoned surface mines. Preliminary results from these studies are promising, but whether they will be viable at scale remains a huge question.

There is no silver bullet solution for repairing the damage to landscapes done by surface coal mining in the tropical forested landscapes of East Kalimantan. This degradation level means that restoration is exceptionally challenging, time-consuming and expensive, especially at the scale needed in the region. Therefore, mining should be limited and necessary changes to mine restoration policy should reflect the realistic expectations given the ecological constraints of coal mine restoration. Perhaps the best outcome for abandoned coal mines is for companies to create a mosaic of land uses that all benefit local populations so that people like Jaidun will have avenues to pursue their livelihoods once the coal resource is exhausted.

Acknowledgements:

The authors thank Vivian Breckenridge, David Neidel and Eva Garen for comments and edits on drafts of this article. We also thank PT Singlurus Pratama coal mine for allowing us access to coal mine rehabilitation sites. And finally we thank Balitek KSDA for providing us with resources and research space that made writing this article possible.

Editor’s note: The authors of this article were given access to mining and rehabilitation sites and the assistance of two technicians by mining company PT Singlurus Pratama, and received transportation to the mine and research space from Balitek KSDA. Neither organization was allowed to review this article or had any control over its content.

References:

[1]            Sheoran, V., Sheoran, A. S., & Poonia, P. (2010). Soil reclamation of abandoned mine land by revegetation: A review. International Journal of Soil, Sediment and Water, 3(2). https://scholarworks.umass.edu/intljssw/vol3/iss2/13/

[2]            Otsamo, R. (2000). Secondary forest regeneration under fast-growing forest plantations on degraded Imperata cylindrica grasslands. New Forests, 19(1), 69-93. doi:10.1023/A:1006688022020

[3]            Parrotta, J. A., Turnbull, J. W., & Jones, N. (1997). Catalyzing native forest regeneration on degraded tropical lands. Forest Ecology and Management, 99(1), 1-7. doi:10.1016/S0378-1127(97)00190-4

[4]            Lamb, D., Erskine, P. D., & Parrotta, J. A. (2005). Restoration of degraded tropical forest landscapes. Science, 310(5754), 1628-1632. doi:10.1126/science.1111773

[5]            Woodbury, D. J., Yassir, I., Arbainsyah, Doroski, D. A., Queenborough, S. A., & Ashton, M. S. (2019). Filling a void: Analysis of early tropical soil and vegetative recovery under leguminous, post‐coal mine reforestation plantations in East Kalimantan, Indonesia. Land Degradation & Development, 31(4), 473-487. doi:10.1002/ldr.3464

[6]            Koutika, L.-S., & Richardson, D. M. (2019). Acacia mangium Willd: Benefits and threats associated with its increasing use around the world. Forest Ecosystems, 6(1). doi:10.1186/s40663-019-0159-1

[7]            Parrotta, J. A., & Knowles, O. H. (1999). Restoration of tropical moist forests on bauxite-mined lands in the Brazilian Amazon. Restoration Ecology, 7(2), 103-116. doi:10.1046/j.1526-100X.1999.72001.x

[8]            Novianti, V., Choesin, D. N., Iskandar, D. T., & Suprayogo, D. (2017). Plant species from coal mine overburden dumping site in Satui, South Kalimantan, Indonesia.  Journal of Degraded and Mining Lands Management, 4(4), 927-936. doi:10.15243/jdmlm.2017.044.927

[9]            Ahirwal, J., & Pandey, V. C. (2020). Ecological rehabilitation of mine-degraded land for sustainable environmental development in emerging nations. Restoration Ecology. doi:10.1111/rec.13268

[10]         Parrotta, J. A., & Knowles, O. H. (2001). Restoring tropical forests on lands mined for bauxite: Examples from the Brazilian Amazon. Ecological Engineering, 17(2), 219-239. doi:10.1016/S0925-8574(00)00141-5

[11]         Chokkalingam, U., Bhat, D. M., & Von Gemmingen, G. (2001). Secondary forests associated with the rehabilitation of degraded lands in tropical Asia: A synthesis. Journal of Tropical Forest Science, 13(4), 816-831. http://www.jstor.org/stable/43582374