Changes in plant community and soil ecological indicators in response to Prosopis juliflora and Acacia mearnsii invasion and removal in two biodiversity hotspots in Southern India

Invasion of alien plant species can alter local plant diversity and ecosystem processes closely linked to soil organic carbon (SOC) and nutrient dynamics. Soil ecosystem processes such as microbial respiration and enzyme activity have been poorly explored under alien plant invasion and especially following invasive plant species removal. We studied the impact of Prosopis juliflora and Acacia mearnsii invasion and subsequent removal on local plant community composition and diversity and on soil microbial respiration and enzyme activity in two biodiversity hotspots in Southern India. Removal of Prosopis promoted recolonisation of local vegetation as indicated by a 38% and 28% increase in species richness and ground vegetation cover, respectively, compared to an unremoved site. Prosopis and Acacia removal led to a significant reduction in soil microbial biomass C (MBC), respiration, dehydrogenase and urease activity due to increased microbial respiration and N mineralisation rate. Higher metabolic quotients qCO2 in soil at Prosopis and Acacia removed sites indicate that MBC pools declined at a faster rate than SOC, resulting decreased MBC/SOC ratios compared to their respective removed sites. Natural and undisturbed ecosystems maintain more SOC through increased belowground and aboveground C input in the soil, resulting in a higher MBC content per unit SOC. Our results indicate that the interaction between above- and below-ground communities is a critical factor determining the structure and dynamics of local plant communities, especially in ecosystems affected by plant invasions

Re-colonizing Mangrove species in tsunami devastated habitats at Nicobar Islands, India

Mangrove habitats are crucial for maintaining the biodiversity of coastal ecosystem. Climatic change, sea level rise and anthropogenic pressures are the major threats to mangrove forests. The Nicobar Islands comprised one of the pristine mangrove stands in India. The mega earthquake of >9 M and subsequent tsunami during 2004 caused destruction of over 70% of mangrove vegetation in Nicobar Islands. The present study was carried out in the Central Nicobar Group of Islands (Camorta, Nancowry, Katchall and Trinkat), where tsunami has entirely wiped out the mangrove vegetation. Re-colonization started on its own course. We enumerated nine species of mangrove plants and 30 species of mangrove associates from the surveyed locations. Lumnitzera racemosa has been recorded for the first time from the study area. Rhizophora mucronata and Bruguiera gymnorrhiza were the common pioneer mangrove species. Long-term monitoring of re-colonization process will help us in understanding succession of mangrove forests

First report on the occurrence of Avicennia marina (Forssk.) Vierh. (Acanthaceae) in the Nicobar archipelago

The 2004 Sumatra-Andaman earthquake (9.2 Mw) and tsunami that followed it resulted in uplift and subsidence across the Andaman and Nicobar archipelago. This unusual natural event severely affected the mangrove and coastal ecosystems across the Andaman and Nicobar Islands. The tsunami and land drowning of 1.1-2.85 m resulted in considerable loss of mangrove habitats in the Nicobar archipelago. Meanwhile, the land drowning also created new intertidal habitats in the earlier terrestrial zones that are now providing suitable conditions for the colonization of mangroves. During the long-term monitoring of mangrove colonization in these new inter-tidal zones, we identified the first occurrence of the Avicennia marina (Forssk.) Vierh. in the Nicobar archipelago. The distribution of A. marina and the characteristics of its colonizing sites are discussed herein

Angiosperms of Nanmangalam Reserve Forest, an urban forest in Metropolitan Chennai, India

Humans have altered the forests of urban regions drastically, thereby reducing the original forests to isolated fragments. Such fragments may contain remnants of the original vegetation. Nanmangalam Reserve Forest (NRF), located in the Metropolitan Chennai, Tamil Nadu, India, is an example of such a forest fragment, covering an area of 321 ha. A total of 449 angiosperm species belonging to 313 genera representing 83 families were recorded from NRF. Amongst the species, 79% were dicots and 21% were monocots. The most genera/species rich families were Fabaceae (37/69) and Poaceae (34/52). The species rich genera included Cassia (10), Crotalaria (7), Erogrostis, Hedyotis and Phyllanthus (6 each). Six endemic species were recorded. This diversity amidst a rapidly expanding city has to be protected in order to enable the conservation agenda of urban areas