5.4.1 Today's ecology
Vegetation
Probably 99.5 percent (See footnote 16) of the original forest cover has now been lost. Only in the Botanic Garden are there remnants of the podocarp and broadleaf rainforests.
There are over 238 hectares of native-dominated vegetation on the Town Belt, most of it in an early stage of regeneration (see map on the next page). It is made up of native forest (186.2ha), native scrub/shrubland (24.9ha), mixed shrubland (exotic-native) and areas recently revegetated with natives (26.9ha). (Section 8 has maps of vegetation cover for each geographic sector.)
Town Belt vegetation generally has the following characteristics:
Plant communities are young (less than 150 years old), simple in structure and with a limited diversity of native species.
Podocarp and most native broadleaf species, and therefore their seed, are absent.
The areas of native vegetation are discontinuous.
A well-developed naturalised flora is present, including weeds.
Pest plants and other weeds are a widespread threat, with some major infestations of invasive weeds.
Areas not in native or exotic tree stands are either managed as grassed playing fields and passive recreation areas or they are scrub- covered.
There are around 600 plant species on the Town Belt, including plants indigenous to Wellington, naturalised plants and weed species. Surveys in 1991 found that at least 150 locally indigenous plant species were growing on the Town Belt. While weeds threaten the development of native vegetation, some exotic vegetation can contribute to the health of indigenous populations.
The eucalypts, for instance, provide a food source for nectar feeders; pine forests support orchids, ferns and native shrub understoreys in places; and areas of exotic scrub (often gorse and broom) can support the regeneration of native bush if left undisturbed and kept weed-free and safe from fires.
Animals
Indigenous fauna is reduced in its species diversity as a result of historic habitat loss and fragmentation, reduced food supply through the reduced diversity of native plant species, and pest competition and predation. Only common native bird species were present on the Town Belt in the early 1990s (of which only fantail, grey warbler and silvereye were numerous); five species of native lizard; and only common insect species. However, pest-control programmes and the conservation work at Zealandia appear to be benefiting the Town Belt's native birdlife. In addition to the common species, bird
monitoring in 2011 and 2012 has shown tui, kereru and kaka using the Town Belt. Whitehead, North Island robin and saddleback are also found in the Town Belt near Zealandia, and informal sightings of kingfishers and ruru/morepork have been reported.
Eight species of introduced mammal are present in addition to introduced birds and insects.
Footnote16: Natural Wellington. A Plan to Preserve and Enhance the Natural Treasures of Wellington City, Wellington Branch, Royal Forest and Bird Protection Society of NZ Inc, 1990. End of Footnote
Page 41 Map:
Native vegetation on Town Belt Transcriber's Note:
Map key follows.
End of Note.
Native Vegetation
Suburbs End of Map.
Page 42
Freshwater ecosystems
The Town Belt's freshwater ecosystems include permanent and intermittent streams, and seepages. Koura, eels, banded kokopu and other aquatic life occur in some streams but these ecosystems have been adversely affected by streams being piped underground for some or all of their length; by drainage works in stream beds; obstructions, such as culverts, to fish passage; and by pollution carried in stormwater runoff.
Forest succession
When forest re-establishes on a bare site, it develops in successional stages.
Typically, in Wellington's broadleaf/podocarp forests these stages would have been:
1. a short-lived phase when ferns and low-growing herbaceous plants colonise the site
2. shrubs emerge through the ground-level colonisers 3. young trees over-top the shrubs to form low-forest cover
4. eventually tall trees such as podocarps emerge through the low forest to form the mature forest canopy.
This process can take several hundred years. However, if the seed of a tall tree lands in a favourable site, courtesy of a passing bird or the wind, it may germinate and become established during an earlier stage of the natural succession.
On the Town Belt today, limited seed sources may delay the successional process from progressing beyond the low-forest cover and the healthy development of forest is threatened by plant and animal pests.
5.4.2 Ecological values
The Town Belt has long been valued as an easily accessible place where people can experience and view nature.
Historically, the mass plantings of exotic conifers and other amenity plants were promoted by councillors and citizens to embellish the Town Belt with trees for the ornamentation of the city and to create pleasant places for recreation. While these values still remain, an important shift in attitude has
occurred: 91 percent of residents surveyed in 2009 thought it was important to use native vegetation on the Town Belt and 93 percent valued the protection of native habitat for birds and other animals.
The importance of indigenous biodiversity and ecosystems in sustaining healthy living environments for people has also been recognised in such documents as the Council's Biodiversity Action Plan 2007.
The Town Belt is part of Wellington's urban ecology. It also plays an important role in linking habitats and ecosystems across the city.