Forest Ecology and Management
Impact of anthropogenic disturbance on pollination and seed dispersal of canopy trees in the wet
evergreen forests of Western Ghats, India.
Investigator: T.Ganesh
Location: KMTR
Duration: 2 years
Planning long-term conservation of biological diversity in tropical forests
can be effective only if we understand the impact of anthropogenic threats
on ecosystem functioning. Two key ecosystem functions, involving plant-animal
interactions, are pollination and seed dispersal. These are essential to
maintain ecosystem health, especially in the context of forest regeneration.
Human induced forest degradation often leads to disruption of such interactions,
resulting in poor fruit production and seed germination, thereby affecting
forest regeneration. It is essential to study these two functionally linked
processes together, as it will identify interaction failure at the level of
pollination and seed dispersal. Unfortunately, there are hardly any studies
in the tropics that address these processes together. In the Western Ghats
of India, a mega-diversity site, large portions of forests are in various
forms of degradation and suffer from poor regeneration. This study proposes
to: 1) quantify the impact of rainforest degradation on the pollination and
seed dispersal success in a wet forest site, and 2) investigate the consequence
of pollination failure and poor dispersal on the regeneration of canopy
trees in the forest. This research will identify canopy and sub-canopy
tree species that are critically dependent on animals to maintain viable
populations and also species vulnerable to human-induced forest disturbance.
Progress
So far detailed results have been obtained for two climax tree species, a canopy tree
and an understorey tree. Both were pollinated by animal vectors, but one is dispersed
by birds while the other is passively dispersed. The species varied in their response
to disturbance. The passively dispersed species produced lower number of fruits in
disturbed sites while the bird dispersed species produced marginally more fruits in
disturbed sites. This could partly be due to the fact that the passively dispersed
species had a more diverse assemblage of flower visitors in undisturbed site while
the bird-dispersed species had greater visitor diversity in disturbed site. Clearly,
disturbance affects plant-animal interactions but this effect is not uniform across species.
Regeneration of the species across the undisturbed and disturbed site was quantified
for the passively dispersed species. Regeneration was at least 4 times less in a
disturbed site compared to the undisturbed site. Since the fruit production for this
species is also low in disturbed site, the fall in saplings could partly be due to
fewer fruits available for germination. Therefore it appears that even for species
that are not depended on animal vectors for seed dispersal, failure at the pollination
level can directly affect regeneration.
Outputs
Preliminary indications show that the effects of disturbance are not uniform across
species and one needs to be cautious when generalizing.
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