Abstract:
Invasive species are the second largest threat to biodiversity loss in the world. Clidemia hirta is a
common invasive species found in disturbed sites such as along forest foot paths in tropical
lowland-wet evergreen forests of Sri Lanka. Comparative information on seed biology of
invasive species with that of the native species in the same habitat is crucial for the management
of invasive species. Thus, we studied the seed biology of Clidemia hirta with that of three native
species, Schizostigma hirsutum, Melastoma malabathricum and Plecranthus kanneliyensis that
share the same habitat of C. hirta. Mature, ripen fruits of all the species were collected from at
least ten individuals in Sinharaja rainforest and transported to the University of Peradeniya and
experiments were initiated within 2-3 days of seed collection. Seed Moisture Content (SMC) was
determined through the oven dry method. Seed germination was studied at 25 or 32o C in light/
dark (12hrs/12hrs), dark and green light regimes. SMC of all the studied species were <15%
indicating that they were orthodox in seed storage behaviour. Thus, they all have the ability to
produce a soil seed bank easily. S. hirsutum, P. kanneliyensis and C. hirta seeds germinated to
100, 77.5 and 95.5% in light/dark conditions, while only 53.3% of the M. malabathricum seed
germinated within 30 days, their T50 values were 26, 24, 32 and 36 days, respectively indicating
that seeds of all the studied species are nondormant. However, none of the seeds germinated in
complete darkness and under green light, except for S. hirtusum which show only 10 and 30%
germination under above conditions, respectively, revealing that seeds of all the study species
required full or partial light conditions for their germination. Thus, seeds that burry in the ground
could also easily form a soil seed bank. Further, the germination traits of all the study species
seemed to be adapted to their habitat conditions. Light requirement for germination may allow
them to select open disturbed habitats with suitable light conditions. Our study revealed that seed
germination behavior of the invasive species C. hirta is similar to the native species that share
the same habitat. Thus, introduction of native species adapted to same habitat soon after the
mechanical eradication of C. hirta could be suggested for management of C. hirta invasion along
the footpaths in the tropical lowland wet evergreen forests.
