Plant Controls: Mangroves
In the past half century, mangroves have increased in extent in estuaries and tidal creeks throughout the upper half of the North Island.
While mangroves are native to New Zealand, and an integral part of functioning estuaries, their relative increase and association with fine sediments has resulted in many authorised (and unauthorised) ‘mangrove restoration’ trials. Unlike the rest of the world where mangroves are declining, in New Zealand these restoration trials involve the removal of mangroves, with goals of estuarine areas returning to prior sandier, unvegetated states, ideally with abundant shellfish resources.
Mangrove restoration programmes have been reasonably well documented by Environment Waikato and Environment Bay of Plenty, particularly those in Whangamata and Tauranga Harbours. NIWA is working with both councils to examine success of mangrove restoration methods and develop best practice for mangrove rehabilitation based on long-term analysis of locations where mangroves have been removed. We will look at identifying barriers to restoration after mangrove removal, for example sediments or organic material remaining from mangroves that result in long-term barriers for successful colonisation by shellfish. We are also looking at effects on neighbouring sandflats, shellfish beds, and seagrass meadows of the mangrove removal methods to make sure that the mangrove removals do not have negative effects on other important estuarine habitats.