The Mountain Apple – An Invader’s Impact 100 years on
In about 1917 someone brought a small, fast-growing tree called Bellucia pentamera from South America and planted it in Indonesia’s gorgeous Bogor Botanical Gardens. Called the mountain apple, its fruits were used by some indigenous people in the Amazon to help with parasite infections.
Now, just over a century later, the mountain apple is flourishing across Asia, mostly thanks to its small seeds which are widely transported by birds and bats. And it is a familiar face on Borneo's Gunung Palung National Park, home to some of the last big areas of lowland rainforest in Southeast Asia and an area rich in seven different types of rainforest.
The mountain apple loves deforestation
Intense logging between 2000 and 2002 helped the invader spread, taking out most of the biggest, most valuable trees and leaving huge gaps in the canopy, which in turn heated the forest floor and ruined the essential shade beneath. But one resident really doesn't mind these new conditions. In fact the mountain apple withstands the hot sun, so much so that it actually out-competes native light-loving species.
PhD student Christopher Dillis of the University of California and his team compared the fruiting frequency of Bellucia to native trees. They found that, on average, 56% of Bellucia in Gunung Palung National Park produced fruit every month, against just 4% of native rainforest trees.
Why does Bellucia love logging?
Canopy gaps are not uncommon. So why is Bellucia more attracted to logged areas than natural canopy gaps? Bellucia trees in gaps created by logging produced more fruits than Bellucia growing in natural canopy gaps, and nobody really knows why. It might be that the intense light in logging gaps lets the trees grow particularly big leaves, which mean more photosynthesis and more energy, which gives it a competitive advantage.
We already know that plant diversity is vital for the health of rainforests, and every other kind of forest. Logging in Gunung Palung has decreased but still continues. Large-scale oil palm agriculture doesn't help. Thankfully, unlike some invaders, Bellucia doesn't run rampant through pristine jungle. It needs logging gaps. But it just goes to show how very damaging even the least dodgy invaders can be if left to its own devices.