Mangrove forest located at the Mai Po Nature Reserve in Hong Kong is impacted by the invasion of the South American vine- Mikania. micrantha. This species creates competition for light with mangroves because M. micrantha, climbs the mangroves and creates a dense layer of leaves on top of the mangrove’s canopy. Reduced light availability reduces carbon uptake, and can potentially result in carbon starvation and death of mangrove individuals. We hypothesized that lower light availability in invaded sections of mangrove canopy would decrease gas exchange, and that leaf structure might reflect lower light availability. We tested this hypothesis by taking the stomatal conductance, water potentials, specific leaf weight, and leaf area index for two species of mangroves- Aegiceras corniculatum and Kandelia obovata. We then tested two methods of clearing the vine, one by cutting off the lower half of the vine and letting the vine on top of the canopy die and the other by removing all of the vine from the canopy of mangrove individuals. We again measured stomatal conductance, water potentials, and leaf area indices about five days later after removal of M. micrantha to see if the change in leaf area index increased gas exchange. We saw that for both Aegiceras corniculatum and Kandelia obovata there was a higher stomatal conductance for the leaves that were not covered by the vine.
Results/Conclusions
Pre-dawn water potential of Aegiceras corniculatum was significantly less negative than Kandelia obovata. There was no significant difference between mid-day water potential. Stomatal conductance was greater for uncovered leaves realitive to covered leaves and the entire removal of the vine led to a reduced stomatal conductance of the leaves because when expossed to full light the leaves wilted. This result is supported by the significantly lower specific leaf mass of leaves from covered areas of the trees. Our results suggest that wholesale removal of the vine from the canopy may be disadvantageous in the short term, and that cutting the vine at ground level and leaving the vine on the canopy may be a better management strategy.