To Plant or Not to Plant, That Is the Question: Reforestation vs. Natural Regeneration of Hurricane-Disturbed Mangrove Forests in Guanaja (Honduras)

Abstract

Background and Objectives: Mangrove forests offer many essential ecosystem services, including the protection of (sub)tropical coastlines, their inhabitants, and the infrastructure from severe storms and tsunamis. However, mangroves themselves suffer severely from such phenomena. After such events, reforestation efforts are widely undertaken to facilitate the recovery of the mangroves. Many of these laborious activities, however, fail for a number of reasons. Material and Methods: In October 1998, the Honduran Island of Guanaja was severely hit by Hurricane Mitch, and, after the storm, almost all of the mangrove forests (97%) were rated as dead. Seven years after Mitch, a longterm survey on the regeneration of the mangroves started. Field samplings in six variably disturbed mangrove zones was conducted in 2005, 2009, and 2016. Along permanent line-transects, all living plant species were recorded for statistical analyses and for quantifying progress. In this paper, the focus is on the three most severely hit areas. In two of them, planting efforts were carried out while the third one was left to regenerate naturally. This setting allowed a direct comparison between natural and human-assisted regeneration processes under otherwise similar conditions and equally severe previous disturbance. Results: Reforestation measures were characterized by high mortality rates of Rhizophora mangle L. propagules planted predominantly. Some, however, surely survived and might have contributed to regeneration after the disturbance. In 2016, roughly two decades after Hurricane Mitch, low-growing Rhizophora mangle forests, with high ground cover, were found. Surprisingly, the area without any planting also witnessed similar mangrove rejuvenation in the same period. Conclusion: Findings on the recovering mangroves in Guanaja confirm the lessons learned from other mangrove rehabilitation measures: planting mostly fails and commonly does not accelerate the revegetation of disturbed forests. In naturally regenerating forests, recolonization may occur after a certain time-lag only if few diaspore sources survived in the surrounding; as soon as established mangrove plants bear propagules, a quick return to viable forests takes place, proving the high resilience of these coastal ecosystems.