Tougher seeds and seedlings of invasive plant species

05 Nov 15 NUS scientists discovered that the tropical American tree that is rapidly spreading in Singapore has greater chance of germination and survival than the local ecological counterpart.

Species that are introduced from elsewhere can sometimes establish self-replacing populations, spread rapidly from the original site, and cause ecological or economic damage. Such invasive plant species often outperform local, or native, plant species in terms of attributes such as growth rates.

Snakewood, Cecropia pachystachya, is a tree found in forest edges and disturbed environments in tropical South America. This species has been documented to be rapidly spreading throughout Singapore and Java. In experiments carried out as part of his Honours Year Project supervised by Prof Hugh TAN and Dr CHONG Kwek Yan from the Department of Biological Sciences, and Prof YAP Von Bing from the Department of Statistics and Applied Probabilit in NUS, Mr Mark RAPHAEL found that seeds of Cecropia pachystachya germinate and grow faster than the native giant mahang, Macaranga gigantea, and the seedlings have higher rates of survival. Further, although both species are supposed to be light-demanding, Cecropia pachystachya was able to germinate under half-shaded conditions, while Macaranga gigantea seeds could not. These results raise the spectre of the non-native species displacing the native from forest edges and tree fall gaps here in Singapore and around the region.

Further work by the scientists have quantified the rate of spread of Cecropia pachystachya in Singapore. Aside from this, the team is also researching the possible impacts of the tree on the soil and other plant species.

A seedling of the snakewood tree, Cecropia pachystachya, recruiting in a reforestation plot in a nature reserve. [Image credit: Chong Kwek Yan]

Reference

Raphael MB, Chong KY, Yap VB, Tan, HTW. “Comparing germination success and seedling traits between exotic and native pioneers: Cecropia pachystachya versus Macaranga gigantea.” Plant Ecology. 216 (2015) 1019.