When nature needs a helping hand: Different levels of human intervention for mangrove (re-)establishment

Abstract

Protecting existing mangrove forests is a priority for global conservation because of the wide range of services that these coastal forests provide to humankind. Despite the recent reduction in global rates of mangrove loss, high historical loss rates mean that there are at least 800,000 ha globally that are potentially suitable for mangrove re-establishment. Recently deposited mud banks or intertidal, previously terrestrial, land might provide additional habitat for expanding mangrove areas locally. There is a long history of mangrove rehabilitation. However, despite numerous good examples of, and growing expertise in, natural or assisted (re-)establishment activities, most mangrove planting efforts, for instance, either fail entirely or meet with only limited success. Exposed to waves and currents and subject to tidal inundation, mangroves differ from terrestrial forests, and approaches to, or tools for, terrestrial forest restoration cannot easily be transferred to mangrove forests. Successful mangrove (re-)establishment usually requires a robust understanding of the abiotic and biotic conditions of the chosen site, the ecological requirements of the mangrove species used or facilitated, the reasons for previous mangrove loss or degradation, as well as the barriers–both societal and ecological–that have prevented natural recovery to date. Because most mangrove forests are socio-ecological systems, with which local human populations are intimately engaged, (re-)establishment will normally require the support of, and engagement with, local communities and other local stakeholders. Here, we summarize where, when and why (re-)establishment of mangroves is needed and how to assess this need. We discuss a range of potential aims and goals of mangrove (re-)establishment along with potential pitfalls along the way from conceiving the initial idea to its realization. We compare different technical and conceptual approaches to mangrove (re-)establishment, their challenges and opportunities, and their design and financial requirements, as well as potential solutions. We ground our final outlook and recommendations on examples of successful efforts and the factors that rendered (re-)establishment successful in the past.

Functional composition outweighs taxonomic and functional diversity in maintaining ecosystem properties and processes of mangrove forests

“…Our findings, on one hand, pledge for protecting species‐rich mangrove forests that support MEPP without human intervention, such as in the old‐grown and highly diverse SRF (Rahman et al., 2019; Rahman, Hossain, et al., 2015; Rahman, Kabir, et al., 2015; Rahman, Khan, et al., 2015). On the other hand, our findings imply that well‐designed mangrove (re‐)establishment strategies (Zimmer, 2018; Zimmer et al., 2022) that focus on a few regionally dominant species, for example, with large leaf area and high leaf litter nitrogen content, along with adding some functionally different species to support a distinct functional composition of the community would help to enhance ecosystem service‐provisioning. This ecosystem codesign approach (Zimmer, 2018) aims to implement simple communities with traits that drive those ecosystem properties and processes essential to key ecosystem services that are most demanded by local societies (Zimmer et al., 2022).…”

What is the ecological footprint of aquaculture after 5 decades of competition between mangrove conservation and shrimp farm development?

“…Abandoned shrimp farms should be used to restore lost mangroves. However, as these shrimp ponds tend to be very deep, varied ecological engineering activities, which may involve the opening of tidal channels, flattening of pond walls or building up of islands inside the ponds should first be undertaken to make the area suitable for mangrove restoration (Zimmer et al, 2022). (Harkes et al, 2015) when implemented in Sri Lanka and other countries facing similar socio-ecological challenges will promote a sustainable shrimp farming industry.…”

Do ecosystems have functions?

“…This critique of an anthropocentric perception of ecosystems certainly goes in line with our argument. While Karr et al (2022), in their reply to Rohwer and Marris (2021), refer to the concept of ecosystem disintegration, meaning the loss of integrity, as being central to ecosystem conservation and re-establishment (sensu Zimmer et al, 2022) and even to our very understanding of human impacts on ecosystems, we follow Rohwer and Marris (2021).…”