Ecological Tipping Points in Mangrove Ecosystems

Mangroves provide a wide variety of ecosystem services to some of the poorest people on the planet. Under natural conditions, mangroves can persist in an incredibly improbable edaphic (“soil”) environment, characterized by repeated wave action and high salinity, by modifying their internal environment with roots, stems and canopy.

Increasingly, however, mangrove systems are subject to over-exploitation, and these degrading systems are prone to passing ecological “tipping points” where positive feedbacks lead to irreversible ecosystem loss. Whilst these tipping points are recognized anecdotally, quantitative understanding is lacking. Consequently, the maximum “safe” level of exploitation is unknown, and, perhaps more importantly, the minimum design requirements for interventions to restore lost mangrove systems are also unknown.

Using a combination of computer simulation modelling, ground-based data collection, and remote sensing image analysis, this project will consider two such tipping points:

1) Wave energy - in relatively intact systems, stem density is high enough to provide suitable physical conditions for seed establishment, because high sedimentation rates allow the formation of soil, and low wave energy inputs allow seeds to anchor themselves. As stands are degraded, stems and roots are lost, incoming wave energy increases and eventually becomes too high for seeds to establish.

2) Solar radiation - As mangrove canopy cover is reduced, more solar energy reaches the soil surface, increasing surface evaporation, which leads to hyper-saline conditions, loss of tree productivity and a consequent further loss of canopy cover.

Fieldwork will take place in Madagascar in collaboration with Blue Ventures Conservation. Full training in simulation modelling, remote sensing and GIS will be given in partnership between Bangor and Lancaster Universities.