Salvaging and replanting 300 mangrove trees and saplings in the arid Arabian Gulf

Abstract

Construction works along a causeway at Mubarraz Island near Abu Dhabi, United Arab Emirates, in the Arabian Gulf necessitated the salvaging and replanting of 300 mangroves (Avicennia marina). Mangroves were excavated manually by shovel (smaller trees and saplings) or mechanically using a backhoe excavator (larger trees), transported with the root ball wrapped in burlap and replanted in a newly created tidal channel. Relocated mangroves were exposed to two different watering regimes and two tidal inundation levels, and were monitored for survival, plant height and leaf health (percentage of green leaves) at 0 and 1 weeks, and then at 3, 7 and 12.5 months. Tree mortality was high in the first week (24%) in mid-summer, with further losses (43%) during the next 3 months. After 12.5 months, 31% of the transplanted trees had survived. There was a significant effect of the duration of tidal inundation on survival and leaf health (higher survival in shallow than deeper plots). There were no significant effects of initial tree height or freshwater treatment on survival or plant performance. These results demonstrate that salvaging of larger mangroves is technically feasible, potentially providing faster ecosystem services (e.g. shoreline protection, source of new propagules) than newly planted seedlings in arid regions where growth is extremely slow.

Quantitative Analysis of Methodological and Environmental Influences on Survival of Planted Mangroves in Restoration and Afforestation

“…Indeed, previous studies involving Avicennia marina have shown that larger transplanted seedlings survive better than or equal to medium-sized individuals and exhibit greater increases in plant height and leaf production than small individuals [45]. Saplings, being the largest life stage typically used in mangrove restoration projects (except for the few studies that have employed adult trees [31]), appear more able to withstand higher exposure to waves and wind that often characterize fringing habitats [23]. It is interesting to note that there were no reported studies using the less-developed propagules of pencil-rooted mangroves (i.e., seed capsules or fruits), although it remains unclear as to whether this is due to recording bias or whether this is due to experience learned by practitioners.…”

“…For each study, information was extracted in relation to the length of time plants were maintained in a nursery prior to planting, any reports of after-care, such as supplementary watering or the removal of debris, and the main reason for mortality, if available. After-care was defined as ongoing actions, such as monitoring, guarding the plantation to avoid improper use, removing plastic debris, restricting trampling and watering, all of which have been shown to enhance survival rates [30,31]. The reasons for mortality were grouped into five categories, described as: 'abiotic' (e.g., salinity, wave energy, light exposure), 'site suitability' (e.g., high or low inundation, planting area), 'competition' (e.g., nutrient limitation), 'predators' (e.g., monkeys, crabs, goats) and 'methodology' (e.g., use of artificial structures, plantation density), and the prevalence of these factors was calculated from all reported studies.…”