The humble termite might have a role to play in rainforest regeneration.
Termites, famously destructive, particularly in the tropics, are not popular in regenerated forests.
But ecologist, Dr Baptiste Wijas, of the US-based Cary Institute and the University of Queensland, and a team of collaborators, have been using termites and fungi, both decomposers, to help predict forest health and carbon sequestration rates in replanted sections of Far North Queensland’s Daintree Rainforest.
“People tend to think that by just planting a diversity of trees, these rainforests will regenerate,” Wijas says, “but it’s worth thinking about, should we actually be putting in other organisms as well, to restore other ecosystem processes that help the forest function? In the context of regeneration, no one really thinks about it at all.”
Decomposers such as bacteria, fungi, termites and other insects are essential for recycling nutrients and carbon. Without such organisms, any rainforest would be piled with dead wood and, in the Daintree’s case, cassowary and possum poo.
Wijas and team set up wood blocks in 3 areas in the Daintree National Park to work out how well decomposers were doing. They compared an old growth site, with two which had been replanted, one 4 years previously, the other 8 years before. The rainforest regeneration sites had been cleared for pineapple, bananas and oil palm around 1900, but abandoned in the early 2000’s and replanted with forest trees in 2010 and 2014.
Blocks were checked for fungi and termites at 6-monthly intervals for four years, and decomposition measured.
Tropical rainforest regeneration fieldwork can be challenging. “You’re sweating all the time, and there are plants that want to attack you everywhere,” said Wijas. In one year, the team experienced drought, flooding, fires, temperatures of 45oC, and “a zombie cyclone (Cyclone Nora) that caught us twice,” said Zanne. “It was an epic, biblical year.”
Fungi grew about the same in old growth and replanted forests, but termites were not so active in the new growth, with the wood blocks decaying more slowly. Wijas says this might have been down to number, diversity or maturity of termite colonies.
As slower nutrient and carbon cycling could harm regrowth health and future growth, he and the team came up with an innovative solution: transplant dead wood and its load of fungi and termites and other decomposers. New forests are short on dead wood, so this could stimulate decomposer communities.
“A young, regenerating forest doesn’t have a lot of deadwood in it,” says coauthor Dr Amy Zanne.. “So if you bring in these logs, you’re giving them some food to tide them over while they wait for parts of trees to start falling down.”
Termite mounds were also on the potential transplantation list, “which is something that no one’s really thought about either,” says Wijas.
Others are not so sure.
“I’m not sure I buy that,” says evolutional biologist Professor Nathan Lo of the University of Sydney. “You’d have to put in a hell of a lot to match the amount you have in Old Growth rainforests. I don’t think it’d be feasible to put in enough dead wood to get the termites going. I think you’ve just got to wait until those rainforests grow. It takes years for them to mature, and eventually you’ll get that dead wood being produced, then the termite numbers will rise accordingly. I’m not sure you can speed it up with the methods they’re using.”
Lo was not involved in the research.
The authors acknowledge that there are challenges in this approach to rainforest regeneration, not least of which would be convincing managers to transplant termites into their region. “Many people — forest managers included — don’t really like termites,” Wijas noted. “But they play an important role in having a healthy forest.”
“I guess a young rainforest might also have different termites to it to an old growth rainforest”, says Lo. ”It’s not really well known. No one’s really done that. So, it’s good that they’ve done this study, because it opens up interesting questions about how rain forests develop, and what insects are needed to help them develop.”
“We think termites might be locking up carbon in their nests,” says Wijas. “When they eat wood, they’re not able to digest all of it, and so the faeces they use to build their nests could be quite carbon-rich. They may even lock up more carbon than they emit, but we just don’t know yet.”
“Termites and fungi are absolutely critical to forest function,” said Zanne. “It would be interesting to see who else returns to the regenerating forests if the termites are there — perhaps ants, lizards, and gliders that eat termites. Right now, we just don’t have any idea whether these organisms are coming back in these systems.”
The rainforest regeneration paper was published in the Journal of Applied Ecology.
Rainforest regeneration
