Abstract:
Invasive plant species exert a significant impact on natural regeneration of tropical forests
causing drastic changes in the future stand composition. Small isolated forest fragments
surrounded by human habitation are more prone to plant invasions. Halgolla Forest
Reserve (7018’N; 80031’E) is an isolated tropical lowland rainforest fragment in central
Sri Lanka which is highly disturbed due to logging and illegal land
encroachment. Clidemia hirta (L.) D. Don has established densely at the forest edges of
this lowland forest fragment. Although, many studies have investigated the effect of this
invasive species on standing vegetation, its effect on soil seed banks is poorly understood.
Thus, this study investigated the impact of C. hirta on a seed bank in three habitat types in
the forest; highly disturbed forest edge, less disturbed riverine area, and undisturbed
forest interior. In each habitat type, 30 soil samples (10 × 62.8 cm3
) were collected using
stratified random sampling during dry and wet seasons. The seed bank was estimated by
the germination method. Out of all emerged seedlings, 40.7% was represented
by C. hirta seedlings while identified native seedlings represented 35.7%. The highest
seedling density of C. hirta in the dry and wet season was recorded in riverine and edge
habitats, respectively, though the values were not statistically significant between
habitats. Species diversity and evenness were lower in highly disturbed forest edge in
which the highest relative abundance of C. hirta was observed. The percentage
emergence of native seedlings was negatively correlated with the emergence
of C. hirta seedlings during both seasons. Low representativeness of native plant species
in seed banks compared to C. hirta indicates the threat exerted by this invasive species on
the natural regeneration of tropical lowland forests. Thus, it is crucial to eradicating this
species to conserve the biodiversity of Halgolla Forest Reserve.
Keywords: Clidemia hirta, Invasive species, Regeneration, Soil seed bank, Tropical
lowland rainforest
