Recognition of Invasive Characteristics of Areca triandra Roxb. ex Buch.-Ham. (Arecaceae), an Introduced Palm Species in Sri Lanka

Abstract

Areca triandra Roxb. Ex Buch-Ham native to the Southeast Asian region has been introduced to many tropical areas including Sri Lanka. Although the common occurrence of A. triandra is noticeable in the southwest region of Sri Lanka, there was no prior study and literature available to investigate the aggressiveness and invasive potential of this species. Therefore, the objective of this research was to identify the level of invasiveness and risk level of A. triandra in natural areas by (a) assessing the distribution range, (b) identifying the biological strategies for rapid colonization through a population assessment and reproductive biology assessment. An extensive literature survey was conducted to determine the distribution range of A. triandra in Sri Lanka. A population assessment was conducted in Meethirigala Forest Reserve (MFR) and Yagirala Forest Reserve (YFR). Mature A. triandra percentage, crown cover percentage, and reproductive biology assessment were conducted by establishing six 20 m×20 m plots, and A. triandra seedling percentage was evaluated by using twenty-four 1 m×1 m plots by covering different topographic conditions such as mid-slope and valley. To evaluate the invasiveness and risk level, a protocol for the prioritization of invasive species in Sri Lanka developed by the United Nations Development Organization (UNDP) was used. Results show that the common occurrence of A. triandra was noticeable in the southwest region of Sri Lanka. The abundance of mature individuals of A. triandra account for 57% with an average crown cover of 46% and seedlings account for 69% of the ground layer. The species thrives in locations subjected to natural and anthropogenic disturbances and the high crown cover and dominance of seedlings negatively affect the understory by suppressing native vegetation. This palm is clump-forming with 66% of plants with multiple stems. Sexual reproduction produced a large number of fruits; 150-200 fruits per infructescence and an average of 370 fruits per clump. Direct observation showed that the bright red fleshy pericarp of the fruit attracts frugivores, such as the Asian Koel and Green Imperial Pigeon. Protocol criteria evaluation has resulted in A. triandra being under ―Alert‖ status with the risk level of ―Moderate‖ for the invasiveness under natural conditions. Invasive potential with dense populations, clustering stems, high canopy cover, high fruit production, and effective seed dispersal confirms that A. triandra is displacing and threatening the native ecosystems. Immediate actions should be taken to control A. triandra populations for preventing further spread in natural ecosystems. 
 Keywords: Areca triandra, Arecaceae family, Invasive species, Frugivores, Infructescence