Botanist Newsletter

Issue No. 25, March to May 1999

Weed Training Program Proves its Worth

The city councils weed training program proved its worth last month when John Hopkins, who drives one of the weed harvesters, noted that there was a different weed growing in the river in the vicinity of Kerrs Reach. This was found to be egeria (Egeria densa).
Egeria is a major problem in the North Island but it had not previously been recorded this far South.

The long term saving in maintenance costs if we can eradicate this plant will be substantial.

Why is egeria a problem?

The volume of plant material that egeria is capable of producing could increase flooding.

The way that egeria grows right up to the surface will interfere with recreational use of the river, particularly rowing.

Increased oxygen demand, especially in autumn when plants are dieing back, could be damaging to the river ecosystem.

Egeria has a high potential to spread to all of our rivers, ponds and lakes and cause the same problems there. This would not be confined to Christchurch City either.

NIWA divers have now surveyed a stretch of river and recorded the amount and location of egeria patches. The distribution of egeria was found to be from the upstream end of Kerrs Reach extending downstream to Avondale Bridge.

Ice Plant Scale Insect

Another new pest record, this time an insect, is for ice plant scale (Pulvinaria mesembryanthemi) which is attacking ice plant on the foreshore. The first record in New Zealand for this species was in 1987. The scale is expected to be quite damaging in the first year or two and then the population should settle down. MAF note that the iceplant scale insect is likely to spread throughout New Zealand.

The choice of species used in dune planting will need to be reviewed. This is an example of the risks associated with using exotic monocultures.

Square Sedge

A more positive recent find was square sedge (Lepidosperma australe) near Spencer Park. This is the only definite record we have of this species within Christchurch City boundary, although it is thought to have grown here in the past.

Urban Ecology

There have been several recent events relating to urban ecology. The first was a seminar at Lincoln University and the second was a visit from Steward Pickett who is involved in a large urban ecology project in Baltimore. The benefits of studying urban ecology include:

Improved data

We are obtaining much better data on the distribution, abundance and association of plants, including both weedy and beneficial species.

Better understanding of environmental interactions

The plant data combined with the associated environmental data that we are collecting enable us to gain an understanding of the principle associations and gradients that explain the biological variation in the City.

More targeted management

Arising from these first two points we will be able to establish guidelines and strategies for management of different habitats.

One likely outcome is strategies for dealing with weeds. Another example is that we should soon be able to analyse and map the plant resources available to wildlife, which will identify if there are any gaps that would benefit from additional attention.

Resources for education

Most city dwellers, not surprisingly, spend most of their time in the city. So this is where their main experience of nature occurs. The ability to interpret and explain what is happening around them will enhance peoples appreciation of how ecological systems work.

Weed Poster

There has been significant interest in the Weed Guide. We are now working on a Weed Poster that will be available to the public.

Weed Identification

All of the Works Operations staff have now been through the weed training program. Following these sessions, visits were made to most of the teams in the field, to see how they were getting on. Additional training on particular species that are difficult to identify will be ongoing, e.g. the two umbrella sedges.

Waimakariri Wetlands

Several significant wetlands were visited recently, both of them near the Waimkariri River. One of these, "The Sanctuary" was previously known to the City Council but a second one, "Coutts Island Swale", has only just come to our attention. Both sites are of sufficient quality to rank as Ecological Heritage Sites- this classification may be sought as a future amendment to the City Plan.

The Sanctuary has a canopy of willow but the high value understorey is almost entirely native species such as tutu, coprosmas and ferns.

Coutts Swale is east of Coutts Island Swamp

It is situated within one of the old Waimakariri River course. This wetland has a great number of rush and sedge species. Some parts have a willow canopy but there are also large areas of rush and open sedgeland.

Mosquitoes

A recent workshop held by Crown PublicHealth has highlighted some of the potential for problems if exotic mosquitoes become established. Christchurch is an area of "medium risk" for incursion by new exotic, disease carrying species. This assessment takes into account population growth and density, climate, international visitors, port and airport movements.

Crown Public Health is facilitating an (informal) network of interested agencies. This includes group such as the CCC, MaF, CRC, Waimakariri District Council, AgriQuality, Lyttelton Port Company and Christchurch International Airport.

Monitoring of Ecological Heritage Sites

Several site visits were made to Ecological Heritage Sites as part of the monitoring required under the Resource Management Act. Sites visited included:
EHS 27.05 (Heathcote Valley East branch). This site includes some of the Mt Cavendish bluffs. Several plants of the rare fern Pleurosorus rutifolius were seen.
EHS 14.09 (Foreshore).

Brooklands Weed Plan

A draft of the Brooklands Weed Plan is now complete. Valuable salt marsh at Brooklands Lagoon is being invaded by weeds, including gorse, Spanish heath and pines. Weed control at this site needs urgent attention.

Brooklands Lagoon has very high wildlife and botanical values and is identified in the City Plan as an Ecological Heritage Site. Several invasive weed species are threatening the high ecological values of Brooklands Lagoon by significantly altering the habitat.

Bexley Wetland

The moat between the wetland and the subdivision has been partly formed. Work has stopped in the meantime because of wet conditions. A group of local residents have formed a trust to look after the wetland. It is great to see the increased level of interest in this area.

Related Information: Bexley Wetland News