Facilitate tidal exchange to restore/create brackish/saline swamps from other land uses

How is the evidence assessed?
  • Effectiveness
  • Certainty
  • Harms

Study locations

Key messages

  • Two studies evaluated the effects, on vegetation, of facilitating tidal exchange to restore/create brackish/saline swamps from other land uses or habitat types. One study was in Australia and one was in Thailand.

VEGETATION COMMUNITY                             

  • Overall extent (1 study): One before-and-after study in an estuary in Australia reported that the area of mangrove forest on an island was greater 3–9 years after restoring full tidal exchange than in the years before.
  • Tree/shrub richness/diversity (1 study): One study in a former shrimp pond in Thailand reported the number of mangrove tree species that spontaneously colonized in the six years after restoring full tidal exchange (along with other interventions).


  • Individual species abundance (1 study): One study in a former shrimp pond in Thailand reported the number of mangrove trees, by species, that spontaneously colonized in the six years after restoring full tidal exchange (along with other interventions).


About key messages

Key messages provide a descriptive index to studies we have found that test this intervention.

Studies are not directly comparable or of equal value. When making decisions based on this evidence, you should consider factors such as study size, study design, reported metrics and relevance of the study to your situation, rather than simply counting the number of studies that support a particular interpretation.

Supporting evidence from individual studies

  1. A before-and-after study in 1993–2004 in an estuary in New South Wales, Australia (Howe et al. 2010) reported that after removing culverts to improve tidal exchange to an island, the area of mangrove vegetation increased. Mangrove forests covered 1 ha of the study area two years before culvert removal, 5 ha three years after culvert removal, and 12 ha nine years after culvert removal. Mangroves benefitted from the expansion of intertidal habitat, which provided a suitable physical environment. Other habitats present in the study site included salt marsh vegetation (before: 44 ha; after nine years: 53 ha), tidal pools/mudflats (before: 33 ha; after nine years: 32 ha) and upland pasture (before: 42 ha; after nine years: 22 ha). Methods: The study focused on an island in the Hunter River Estuary, which had been partially drained for agriculture. In 1995, two 0.5-m-diameter culverts in a tidal inlet were removed, restoring full tidal exchange to approximately one fifth of the island. Tidal exchange was slightly improved across the rest of the marsh, where culverts remained in place. Habitats were mapped from aerial photographs taken in 1993, 1998 and 2004.

    Study and other actions tested
  2. A study in 1999–2005 in a former shrimp pond in Thailand (Matsui et al. 2010) reported that six years after restoring tidal exchange (along with reprofiling and planting mangrove seedlings), 1,797 unplanted trees of 15 different species were present. The most abundant species were grey mangrove Avicennia marina (842 trees), Bruguiera cylindrica (486 trees) and Ceriops decandra (267 trees). Four species were represented by a single tree. Methods: In June 1999, full tidal exchange was restored to an abandoned 6,525-m2 shrimp pond by levelling the banks surrounding the pond. Previously, water could only flow in and out through a 10-m-wide channel. The pond was also filled in. In September 1999, seedlings of four mangrove species were planted in the pond (500–800 seedlings/species, 1.5 m apart). The study does not distinguish between the effects of these interventions on naturally colonizing vegetation, of restoring tidal exchange, reprofiling and planting. In October 2005, mangrove trees that had spontaneously colonized were recorded in a 300-m2 section of the site.

    Study and other actions tested
Please cite as:

Taylor N.G., Grillas P., Smith R.K. & Sutherland W.J. (2021) Marsh and Swamp Conservation: Global Evidence for the Effects of Interventions to Conserve Marsh and Swamp Vegetation. Conservation Evidence Series Synopses. University of Cambridge, Cambridge, UK.

Where has this evidence come from?

List of journals searched by synopsis

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Marsh and Swamp Conservation

This Action forms part of the Action Synopsis:

Marsh and Swamp Conservation
Marsh and Swamp Conservation

Marsh and Swamp Conservation - Published 2021

Marsh and Swamp Synopsis

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