It’s difficult to get things growing on degraded lands. Stripped of their original forest cover, drained of moisture, and often contaminated, acidified and/or plagued by salinification, these landscapes often remain bare for decades, leaching high levels of carbon dioxide into the atmosphere in the meantime.
Hence why Center for International Forestry Research (CIFOR) scientist Himlal Baral and his colleagues were thrilled at the sight of the native tree species Pongamia pinnata thriving just 1.5 years after being planted in a trial plot on degraded peatlands in Central Kalimantan, Indonesia. They also observed the native tree species growing well on land formerly used for mining there and in degraded areas in Central Java. “It’s a rocky area with very poor soil – hardly any topsoil – and the pongamia was growing everywhere,” he recalls.
Pongamia is a quick-growing, nitrogen-fixing, wide-canopied tree that is native across much of Asia and the Pacific and traditionally used for fuelwood, animal fodder, shade, soil improvement and medicinal purposes. In the Indonesian archipelago, “you can find it in most places,” said Baral, “but people don’t necessarily know its value or range of uses.”
Now, a new article in the journal Forests, which was co-written by a group of Indonesian and international forestry scientists including Baral, seeks to spotlight this under-sung tropical ecosystem hero by documenting its potential to meet contemporary energy-production, restoration and livelihood goals.
As part of its nationally determined contributions to the UN Paris Agreement on climate change, Indonesia’s government has committed to restoring 14 million hectares of degraded and marginal land – including over 2 million hectares of degraded peatlands – by 2030. According to the study’s authors, pongamia is a compelling option for these restoration efforts, as it is extremely hardy and can thrive in a range of harsh environmental conditions, including extreme heat and dryness, waterlogging, salinity and chemical contamination.
That’s not the only box it ticks, however. “While the government’s ambitions might be primarily about restoration, local people’s interest is in trees that can give them some value or income,” says Baral. Here, too, pongamia punches above its weight: recent studies have found that its high-yielding seeds offer significant potential as a source of biofuel – including as a renewable, bio-based jet fuel that is clean-burning, non-corrosive and has no sulfur emissions.
Because it can be grown on land that has little agricultural potential, the use of pongamia for this purpose avoids the common critiques leveraged at many biofuel crops: that they take up valuable, fertile-soiled spaces that could otherwise be used for growing food. Given the government’s aim to increase the proportion of its energy coming from local renewable sources, growing pongamia for biofuel could well be a wise livelihood choice for locals in degraded landscapes around Indonesia.
There are other potential benefits to smallholders of incorporating pongamia into their farming systems, too. The trees thrive at altitudes from sea level to over 1,200 meters, and as such could prove a promising choice for shade-grown coffee agroforestry. The tree species that Indonesian farmers traditionally use for coffee shading, such as Leucaena leucocephala, “are very prone to invasive pests like Heteropsylla cubana, which is now endemic in the islands,” says Budi Leksono, a professor who works at Indonesia’s Ministry of Forestry and Environment’s Research and Development Agency.
Using pesticides and herbicides to keep these challenges under control negatively impacts coffee’s flavor, and the health of the ecosystem in general. “So our farmers now need alternative species for coffee shading,” he says. Pongamia, with its natural pest resistance and soil-enhancing qualities, is an obvious choice: in 2022, the scientists plan to begin trialing the tree for this purpose in the Balinese highlands.
Carbon credits are another promising possibility for pongamia plantations. “At this particular global moment, you can imagine the carbon [sequestration and crediting] demand is huge – we are getting a lot of inquiries about pongamia for this purpose,” says Baral, noting pongamia’s advantages over other tree crops like teak and mahogany that struggle with permanence due to their high value as timber. “Because the interest [in pongamia] is in the seeds, it means the trees will stay in the landscape,” he says.
However, Leksono notes that “we still have to gather a lot more information on the carbon sequestering potential for pongamia” before accreditation can be properly explored.
And can we eat those vibrant, abundant reddish-brown pongamia seeds? “That’s an interesting question,” laughs Leksono. While locals have traditionally avoided the seeds because of their bitter taste and low-level toxicity, scientists at Californian agricultural technology company TerViva are currently experimenting with treating and processing them into nutritious, tasty, protein-rich oils and flours.
For food or otherwise, it’s clear that planting pongamia on Indonesia’s degraded lands could “fulfill a whole lot of ambitions and address the interests of many different stakeholders – at government, community and international level – all in one go,” says Baral.
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