TRIP REPORT : Measuring indigenous riparian trial plantings

 Saturday 25 September 2004 :   Measuring indigenous riparian trial plantings

A team of eleven assembled at the Maoribank site (on the True Right of the Hutt River) to measure the height and crown spread of the following species planted in 2002 at 1 m spacing in rows of 50: riverside row Phormium tenax, then Phormium cookianum, then Cortaderia fulvida, then Podocarpus totara, then Plagianthus regius.   This bouldery site is overgrown with blackberry and in places silt has almost smothered some plants.   One of the conditions of the trial is that we must not weed the plantings except where weeds make it impossible to take measurements, so secateurs had to be used sparingly.   Maoribank is the best performer of the three sites and most of the indigenous plants are still there.

The second site, on the True Left, opposite Manor Park golf course, is more subject to flooding and is under a tall, dense infestation of fennel, as it was last Spring.   The riverside row here was Dicksonia squarrosa, now all washed away or buried deeply under silt.   Floodwaters have been up to three metres high on several occasions at this site, evidenced by the debris.   The second row is Pittosporum tenuifolium, then Pittosporum eugenioides, then Podocarpus totara, then Plagianthus regius.   Plant numbers are all reduced compared with last year’s results.

The third site, at Avalon, is on the True Left, in two halves, 3A and 3B, one upstream of the other.   Both were already closely planted in 2 m tall poplars when the trial began in 2002.   3A was destroyed by a flood in 2003 which removed about five metres of the bank width.   The substrate is bouldery and frequent floods deposited silty sand to a depth of at least 50 cm, burying many of our plants.   We don’t even know whether they are surviving underneath, because our job was just to measure, not exhume.   The species planted here were the same for 3B: the riverside row, Dicksonia squarrosa, has long gone, and the plants in the other 4 rows are much reduced in number.

The trials are in their second year of five.   Independent monitors Tim Porteous and Tim Park will check the results.   In the next issue of the Newsletter Ian Atkinson will provide statistics.

Participants:   Margaret Aitken, Peter Beveridge, Barbara Clark, Gavin Dench, Bryan Halliday, Dave Holey, Chris Horne, Rodney Lewington, Barbara Mitcalfe (leader / scribe), Darea Sherratt, Sunita Singh.   Steve Murphy represented the GWRC Flood Protection team, and Darryl Kee of Weedworks arrived to deal with OMB at Site 3B.   Apologies were received from Ian Atkinson, Stan Butcher, Patricia Tankersley and Vicky Froude.