Spatio-temporal changes in fringe mangrove extent in Pondicherry, India after two phenomenal perturbations: tsunami and cyclone Thane

Narayanan Ayyappan (1) , A. Stephen (1) , Gowrappan Muthusankar (1) , S. Jeyakumar (1, 2) , J. Presena (3)

1 IFP - Institut Français de Pondichéry
2 VHNSN College
3 Indira Gandhi College of Arts and Science

Growing pressures on mangroves throughout the world, highlight the need for studies of vegetation across spatio-temporal scales even in relict patches for ecosystem conservation. Mangroves experience human pressure due to coastal development and are also subjected to environmental stress such as cyclones, tsunami, floods, and sea-level rise, often taking decades to recover from these stresses. We estimated changes in mangrove vegetation in the Ariankuppam estuary on the southeastern coast of peninsular India after two phenomenal perturbations, the 2004 tsunami and 2011 cyclone Thane. We compared land cover maps of mangroves from 2005, 2010, and 2011 with 2004 mangrove vegetation maps to detect change in areal extent of mangrove zones. We inventoried all stems ≥ 10 cm gbh in 34 quadrats (5 m x 5 m) prior to the 2011 cyclone, immediately following the cyclone, and eighteen months later to document damages and recovery. The site harbours 2988 trees ha-1 for stems ≥ 10 cm gbh. We found four distinct mangrove zones in 2005 (15.54 ha), and five distinct mangrove zones in 2010 (41.73 ha) and 2011 (40.65 ha). The tsunami and subsequent activities such as dragging the boats swept ashore and dredging resulted in 48 % loss of mangroves. The increase in mangrove area observed during 2010 and 2011 was due to the recovery potential of Avicennia and restoration programs. Cyclonic impact and recovery status inventories revealed that among the different zones, the monodominant Avicennia zone experienced severe damage and the mixed Avicennia zone showed slow recovery. The full impacts on the ecosystem from extreme stochastic events; however, can only be determined with long-term monitoring.

Mots clés: recovery; tree density; vegetation cover; Avicennia; disturbance; dynamics; monodominance

Domaines: Ecologie, Environnement

Narayanan Ayyappan, A. Stephen, Gowrappan Muthusankar, S. Jeyakumar, J. Presena. Spatio-temporal changes in fringe mangrove extent in Pondicherry, India after two phenomenal perturbations: tsunami and cyclone Thane. Tropical Ecology, 2016, 57 (2), pp.361-368. ⟨hal-01352517⟩