INVASIVE PLANT SPECIES IN THE DISTURBED FOREST OF BATUKAHU NATURE RESERVE, BALI, INDONESIA

Abstract

Patterns of invasive plant distribution and their underlying mechanisms are complex and vary with spatial scale. Within the mountainous tropical ecosystems of Bali Island, a local scale pattern of invasive plants is still poorly understood. This paper aimed to detect and investigate the presence of invasive species and to evaluate their relative abundance linked to forest site conditions along with an elevation range on Mount Pohen, Batukahu Nature Reserve, Bali, Indonesia. To identify the importance of environmental disturbances on species invasion, the disturbance-environmental factors and the species-environmental relationship were also measured and examined. Using the stratified random sample, 78 vegetation plots of 2 m x 2 m size were established in four forest sites. Ten invasive plant species belonging to ten genera and five families were identified. Of these invasive species, 40% were herbs, while shrubs and grasses comprised 30%, respectively. Austroeupatorium inulaefolium has the highest frequency (45% of plots); followed by Ageratina riparia, and Brachiaria reptans (40% of plots, respectively), Melastoma malabathricum (37%) and Calliandra calothyrsus (27%). Austroeupatorium inulaefolium was the most abundant invader, followed by Ageratina riparia, and the remaining invasive species were Pennisetum purpureum, Calliandra calothyrsus, Imperata cylindrica, Brachiaria reptans, Melastoma malabathricum, Lantana camara, Bidens pilosa and Blumea lacera, respectively. The distribution of invasive plants was strongly linked to the disturbance level of their respective habitat. The largest numbers invasive plants were present in burnt sites close to the forest edges with direct anthropogenic influence, while the undisturbed forest was the least invaded site. Further, the most invasive species mainly occurred at low elevations up to 1600 m a.s.l. and were rarely found at higher elevations. However, few invasive species such as Austroeupatorium inulaefolium and Melastoma malabathricum were able to colonize the highest altitude (2035 m a.s.l.), and to a lesser degree, Ageratina riparia and Brachiaria reptans were also distributed at high altitudes (1950 m a.s.l. and 1972 m a.s.l. respectively). This study provides a fine-scale analysis of invasive species distribution which will serve as a basis for conservation purposes, especially for strategic planning regarding the detection and management of invasive alien plants.