Biodiversity 2003/04

Key points

• Planting alongside streams produces a measurable drop in water temperature
• For the Wairarapa wetlands we have established a benchmark (the number of wetlands and their quality) against which we can measure improvements in their health
• Deer and gots continue to harm our indigenous forests

What is biodiversity?

Biodiversity simply means the variety of all life – plants and animals. New Zealand’s biodiversity is unique because it evolved in isolation from the rest of the world over 80 million years ago. We have a wonderful ‘cargo’ of internationally significant biodiversity. Much of it is vulnerable to the impacts of human activity, habitat destruction and introduced plant and animal pests. The decline in New Zealand’s biodiversity has been described as our “most pervasive environmental issue”.

Since the launch of the New Zealand Biodiversity Strategy in 2000, Greater Wellington Regional Council has been actively working to strengthen regional biodiversity by seeking to protect and improve the ecological health of ecosystems, such as lowland forest, wetlands, rivers and their margins and coastal dunes and escarpments.

Riparian restoration: it works!

Greater Wellington is working on three riparian restoration pilot studies to work out what works best in what places, and to demonstrate the ecological benefits of planting riparian margins. This study has been in progress since 2001. While this is a long-term study, we are already seeing some promising improvements in the overall health of these stream ecosystems.

Bank stability has increased and water temperatures in the planted sections of the streams are less likely to exceed temperatures that are detrimental to fish and macroinvertebrates (insects that live in the water and are a major food source for fish). Along some replanted reaches there has been a decrease in algal biomass and a reduction in siltation. This, as well as an increase in bits and pieces of wood in the stream, has improved the quality of available habitat and consequently increased species diversity and allowed for the return of some of the more sensitive invertebrate species. We expect to see further improvements when the riparian plants grow big enough to start shading the stream.

Click on the thumbnail below to see a graph showing the daily variation in water temperatures upstream and downstream of a planted reach of the Enaki Stream in the first week of February 2003. Temperatures are generally two or three degrees cooler in the planted section than the unplanted section. As the riparian plants grow bigger, they will be able to provide more and more shade so that eventually water temperatures may be kept under 20 degrees throughout the summer. This should bring about continued improvements in stream health and an increase in aquatic biodiversity.

Wairarapa wetland benchmark established

We completed the first comprehensive survey of the state of wetlands in the Wairarapa in June 2004. This will provide a benchmark so that future monitoring will show us whether our programmes are ‘making a difference’.

What did the survey find?

• Wairarapa wetlands have been reduced from a pre-human extent of 78,000 hectares to just 10,000 hectares
• Lake Wairarapa makes up 7,000 of this 10,000 hectares
• 133 wetlands remain (that we know of) with 75% in private ownership
• most wetlands are small – two to three hectares
• nearly half are grazed
• weeds are a problem in many wetlands.

Greater Wellington has established a wetlands programme to address these issues and get the region’s remaining wetlands fenced and well managed.

Pest pressures in lowland forests

Possums

The pie charts show the degree of damage to palatable trees before (left) and after (right) possum control.

Greater Wellington has 17 Foliar Browse Index (FBI) sites in Key Native Ecosystems (KNEs) around the region. Key Native Ecosystems are areas of native bush, dune vegetation and wetlands that we have assessed as being vital to the long-term viability of the region’s unique plant and animal life. At these FBI sites we measure the damage to tree health from possums eating the leaves.

The good news is that many low to moderately palatable species and a few highly palatable species have shown improvement in foliage cover since possum control began (see pie charts above). Foliage damage has reduced significantly in tawa, mamaku, lancewood and totara. The average amount of leaves eaten on all species is low to moderate.

The bad news is that a few moderate to highly palatable species, such as fuchsia, kaikomako, kohekohe and fivefinger, are showing signs of continued susceptibility to feeding by possums. With all trees, possum feeding continues to be a strong influence on low canopy cover scores, with some trees of some species still showing signs of severe browse.

In areas where there used to be a lot of possums, the health of palatable tree species is continuing to decline. It seems that even low numbers of possums may be reducing the ability of some trees to recover from past damage and compete with the vegetation around them.

Goats and deer

Many people are aware of the damage that possums can cause to the indigenous forests. The effects of forest-floor browsers, such as goat and deer, are less well-publicised. Goats and deer selectively graze young, palatable seedlings and disrupt the regeneration process. This causes a change in composition of the forests, which will ultimately affect the abundance of the indigenous birds, lizards and insects - because they need to feed on the fruit and seeds of the trees. On land managed by Greater Wellington, there are a fenced-off areas. These areas exclude goats and deer so that the abundance of seedlings at different growth stages can be measured over time. We can then compare the results with data collected from similar vegetation plots outside the fenced areas (see photos below).

An intensive goat control programme has been underway since 2001 in some of the forested areas managed by Greater Wellington. There has been an increase in the number of palatable seedlings growing past the browse height of 75 cm. If hunting pressure can be continued, biodiversity gains can be expected.

The bush inside the fenced-off area (see photo below left) has many young plants growing while outside the exclosure (see photo below right), there are few seedlings growing more than 75cm high. This is because deer and goats eat the young plants.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

What can you do?

Consider getting together with your neighbours to undertake co-ordinated possum control in your neighbourhood - remember possums eat roses and damage vegetable gardens as well as native bush! Greater Wellington pest animal officers are available to give advice on the best approach. Contact them through our Masterton (06 378 2484) or Upper Hutt (04 526 5327) offices.

If you are fortunate to have a wetland, block of bush or other natural area on your land, consider legally protecting the area by way of covenant. Such protected areas are eligible for assistance with managing any weeds and pests. Assistance is available in some cases to help fence the area from stock. At the very least, Greater Wellington staff can offer advice on how best to manage your special area.

More information

For more information about Greater Wellington’s biodiversity programmes, contact our biodversity co-ordinator, phone 04 384 5708.