Morton (1976) has comprehensively summarized the widely ranging values of mangrove forests, as follows.
1. Ecological value
Mangroves constitute a highly productive estuarine ecosystem of vital importance in animal food webs. Their biological richness isn’t generally appreciated. Ritchie (1976) notes that New Zealand mangroves produce some 10 tonnes of organic plant debris/ha/year and enrich the nearshore environment by a factor of a least 10 over similar coastlines lacking mangroves. They are also the breathing areas of harbours, re-oxygenating water during the ebb and flood or tides.
2. Sedimentation and coastal protection value
With their expansive, shallow root systems festooned with pnuematophores,mangroves have the capacity to trap fine sediment and so build out coastal areas. They thus form an effective buffer zone protecting the shore from the erosive forces of wave action. Indeed, mangroves are often purposefully planted in shore protection works or to shelter wharves and marinas.
3. Wildlife habitat value
Mangrove forests are refuges for a host of bird species including forest birds in the canopy, and waders in the tidal muds. In addition to local species, global migrants, such as godwits and knots, also inhabit mangrove areas.
4. Economic value
There is essentially no direct economic use of mangroves in New Zealand. With several alternative sources readily available, there is no demand for the wood of mangroves for fuel, pulpwood, or building timber. According to Chapman (1976) and Walsh (1977) avicennia isn’t a preferred fuel, nor is it suitable for pulping. Elsewhere, especially in developing countries, it has a few specialized uses, in shipbuilding for example, and for various medicinal purposes. A. germinans is reported to have value as a producer of high quality honey. However, Walsh (1967) notes that honey from the New Zealand mangrove has a most unpalatable flavor and has no commercial prospects.
5. Coastal fisheries value
Much coastal fishery in New Zealand is fundamentally dependent upon mangrove forest. According to Ritchie (1976), at least 30 species of fish use mangrove wetlands at some stage in their life cycle. In north Auckland some commercially valuable species such as eels, flatfish, grey mullett, pipi and cockle are caught almost exclusively in mangrove areas.
6. Aesthetic value
Mangrove forests have traditionally been regarded as unpleasant wastelands. There is even evidence to suggest that clearing of mangroves was often an unwarranted fearful response to the supposed health hazard from mosquitoes and other inhabitants of mangrove wetlands. Despite this long tradition of disdain and fear, many people now view the mangrove forest as a scenically attractive one, making a pleasing panoramic contribution to the shorescape.
7. Scientific and educational values
As a unique amphibious intertidal forest, mangroves are of great botanical interest. They display a fascinating array of physiological and structural adaptions of their demanding and specialized environment, including peculiar breathing roots, or pneumatophores, underground aeration tissues for conducting and storing oxygen, resistant corky bark, and large viviparous seedlings which promote effective dispersal. There is also much scientific interest in the inter-relationships between plants and animals, vegetation dynamics and plant succession, and the role of geomorphic site and history in the establishment and development of mangrove forests. But, all, the new Zealand mangroves are scientifically important because here avicennia is at the poleward limit of its global geographic range, ie at its environmental extreme limits and possibly specially adapted to a temperate climate.