Simulated effects of site salinity and inundation on long-term growth trajectory and carbon sequestration in monospecific $Rhizophora\; mucronata$ plantation in the Philippines

TL;DR

This study presents a mathematical model to evaluate how salinity and inundation affect long-term growth and carbon storage in mangrove plantations, introducing an index to optimize restoration strategies.

Contribution

The paper introduces a novel index, $\xi$, to assess and guide long-term growth and carbon sequestration in mangrove restoration, based on a stochastic growth model.

Findings

If $\xi > 1$, plantations can reach 1000 t/ha biomass in 200-250 years.

Current strategies with $\xi < 1$ lead to declining biomass without intervention.

The index $\xi$ can serve as an early indicator for restoration success or failure.

Abstract

A mathematical model of coastal forest growth is proposed to describe and test the effects of salinity and inundation in the long-term growth performance and carbon sequestration of monospecific mangrove ($Rhizophora\; mucronata$) plantation in the Philippines. We used allometry in expressing the mangrove growth equation, and stochasticity in scheduling population-level events that drive the development of the mangrove forest. Analysis of the model unveils an index, $\xi$, that could be used in assessing a strategy which could promote optimum carbon-stock accumulation in the long run. If initial plot is configured such that $\xi > 1$, the $R.\; mucronata$ plantations could achieve an above-ground biomass per hectare (AGB) of $1000\mbox{ t/ha}$, or about $500\mbox{ tC/ha}$, in approximately $200$ to $250$ years post planting. In contrast, the current restoration strategy implemented in the Philippines corresponds to the case that $\xi <1$. Consequently, the restored mangroves could not achieve stable growth without the support of costly human assistance such as frequent replanting. Rather, through that typical strategy and in the absence of assistance, the AGB decreases with time until all trees die. Mangrove restoration could therefore be planned strategically to mitigate costly and wasteful implementation. The proposed index $\xi$ thus serves as an early indicator for the progress or demise of restored mangroves.