Friday, April 01, 2016

What will climate change mean for Borneo’s carnivorous pitcher-plants?

  • Pitcher-plants of the genus Nepenthes are tropical carnivorous plants that trap and digest insects.
  • Some of Borneo's pitcher plants inhabit a broad altitudinal range in its mountainous forests, while others are limited to a narrow band.
  • Models indicate that one of these narrow-band species will go extinct by 2050 if current warming trends continue.

Nepenthes, or tropical pitcher plants, are a genus of carnivorous plants well known for their intricate and beautiful pitcher-shaped leaves that trap and digest insects. The genus is comprised of approximately 150 species, most of which are endemic to the Old World Tropics.

The greatest diversity of Nepenthes are found in Borneo, Sumatra and the Philippines. Plants within the Nepenthes genus grow within a broad altitude range from sea level to 3,400 meters (11,100 feet). But some species are restricted to narrower ranges, and may face extinction in a warming world.

At 140 million years old, the Borneo rainforest is one of the oldest rainforests in the world. Approximately 15,000 species of flowering plants and 3,000 tree species comingle and compete for space in this dense plant community.

The Borneo rainforest is also home to various indigenous peoples, a treasure trove of medicinal plants, and a rich collection of carnivorous plants. Carnivorous plants can be found throughout Borneo but one especially accessible area to visit tropical pitcher plants is in Bako National Park.

Bako National Park is the oldest National Park in the Sarawak region of Malaysian Borneo. The park is close enough to the city of Sarawak to visit in one day. Once in the park, hikers can explore the intertidal zone of the South China Sea and trek into steep regions of montane forest in the same day. Wildlife is abundant.

One particular trail, the Lintang Trail, leads hikers along mangrove boardwalks near the Park headquarters and up a steep sandstone escarpment. Hikers eventually reach a plateau area that is part keranga, or dry heath forest, and part bare sandstone rock. It doesn’t take a well-trained botanist to spot abundant tropical pitcher plants while hiking around the Lintang trail. 

Nepenthes are everywhere along the trail and appear quite healthy. Multiple Nepenthes species thrive in Bako National Park, but one species, Raffles’ pitcher-plant (N. rafflesiana), is particularly well represented along this trail.

Raffles’ pitcher-plants grow happily in various microenvironments: peat swamp forests, heath forests, cliffsides and keranga forest. Furthermore, this species lives within a broad altitude range, and is found at sea level all the way up to 1,500 meters (5,000 feet).

Thanks in part to its flexible altitude range, this Nepenthes species enjoys healthy population numbers and is currently listed as a Least Concern species on the IUCN list of endangered species.

Now, let’s compare this scenario with another tropical pitcher plant living in Borneo, the large-leaved pitcher-plant, (Nepenthes macrophylla). Unlike Raffle’s pitcher plant, this species can tolerate only a narrow range in altitude, growing exclusively on mossy ridges along Mount Trusmadi between 2,000 and 2,600 meters (6,500 and 8,200 feet) (Clarke, 1997.) Mount Trusmadi is located in Sabah, the eastern region of Borneo.

The peak of Mount Trusmadi sits at 2642 meters (8667 feet), so the narrow altitude range of the large-leaved pitcher-plant extends almost up to the summit. Due in part to this restrictive geographic range, the population of this Nepenthes species is in a precarious situation, and is currently listed as Critically Endangered on the IUCN list.

Okay, so what are the most probable fates of these two different Nepenthes species in the next 100 years as the world warms? Would populations of large-leaved and Raffles’ pitcher-plants be impacted by the predicted rise in global temperatures?