By
Daniel M. Alongi
(
doi:10.1016/j.envsci.2011.02.004 )
Natural ecosystem change over time is an often unconsidered issue for PES and REDD+ schemes, and a lack of consideration of thermodynamic limitations has led to misconceptions and oversimplifications regarding ecosystem services, especially for tropical mangrove forests. Mangroves are non-linear, non-equilibrium systems uniquely adapted to a highly dynamic boundary where shorelines are continually evolving and sea-level ever changing, and rarely conform to classical concepts of forest development and succession. Not all mangroves accumulate carbon and rates of forest floor accretion are directly linked to the frequency of tidal inundation. Carbon payments in either a PES or REDD+ scheme are dependent on the rate of carbon sequestration, not the size of C stocks, so site selection must be ordinarily confined to the sea edge. Gas emissions and net ecosystem production (NEP) are linked to forest age, particularly for monospecific plantations. Planting of mixed-species forests is recommended to maximize biodiversity, food web connectivity and NEP. Old-growth forests are the prime ecosystems for carbon sequestration, and policy must give priority to schemes to maintain their existence. Large uncertainties exist in carbon sequestration potential of mangroves, and such limitations must be factored into the design, timeframe and execution of PES and REDD+ schemes.
