Abstract:
The native New Zealand mangrove Avicennia marina var. australasica is part
of a prominent group of saltmarsh plants colonising the intertidal zone and
forms a major ecological component in many estuaries in northern New
Zealand.
Recently, after concerns raised by community groups and local councils about
a reduction in direct access to water, the recreational and commercial uses of
estuaries, it became clear this single species had become more abundant
within its accepted range as a result of accelerated colonization.
To assess these changes, as well as study the possible link with catchment
management, a forest structure-management model is hypothesized. The
model tests if forest physiognomy can be linked to changes in the aerial extent
of mangals, and consequently catchment management. The model is based
on the characteristics of the four developmental stages as proposed by
Jimenez et al. (1985) as well as a number of physiognomical variables (tree
density and the ratio between tree height and diameter).
The model is tested in four different locations throughout the natural latitudinal
distribution of A. marina. Each area has a different catchment management
history that will cover the full range of perceived catchment management
impacts on estuaries, ranging from minimally to heavily impacted.
Clear differences are detectable in forest structure between the locations, and
these appear related to past catchment management.
It is concluded, based on the interpretation of the findings, that one of the
main factors deficient in the management of mangroves has been the lack of
comprehension of the interconnectedness of coastal, estuarine and terrestrial
systems. Plans for sustainable management are offered for each area, as well
as an overall strategic catchment management plan.