Exploring litter dynamics as indicator of forest recovery in mangrove-recolonized abandoned ponds

Abstract

Aquaculture is the primary driver of mangrove loss in Southeast Asia. Across the region (in the Philippines in particular), most of these ponds are now abandoned and unproductive. Natural mangrove recolonization, post-pond abandonment, is possible, but its potential for mangrove restoration is often overlooked. Knowledge on the recovery (e.g. forest productivity) of recolonized stands is scarce. This study assessed the recovery potential of mangrove-recolonized ponds using litter dynamics as indicator. Litter is a major contributor to forest productivity in mangrove ecosystems. Rates of litter production and decay in mangrove-recolonized fishponds and natural stands (as a chronosequence of different age cohorts) in Oriental Mindoro, Philippines were compared. Production and decay were measured through the litter trap method and the litter bag experiment, respectively. Results indicate that the rates of litter production in natural mangroves (50- and 90-year-old) are two (9.10 ± 2.42 Mg/ha/year) to three (12.40 ± 2.30 Mg/ha/year) times higher than the recolonized ponds (10-year-old, 3.95 ± 0.80 Mg/ha/year). However, comparable rates were recorded between the 30-year-old recolonized ponds (8.86 ± 1.95 Mg/ha/year) and the 50-year-old natural stand. Decay rates between stand types were not significantly different (0.37 ± 0.03 g/day). This indicates that despite existing poor conditions from previous pond operations, naturally recolonized ponds can recover productivity and thus can regain ecosystem functionality. Ignoring or delaying the rehabilitation of abandoned ponds is a lost opportunity for recovering mangrove ecosystem services (e.g., carbon sequestration). Thus, prioritizing mangrove restoration in abandoned ponds is recommended in the Philippines.