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Appendix

The data

Cimino 9 March 2010

Sandspit Road survival bar chart 2009 Rabbits and Pukeko Take Toll: Browsing by rabbits appears to have caused the overall poorer survival of koromiko, at the Sandspit Road trial. The open-ground plants with their greater offering of foliage appear to have been particularly attractive. Root trainer tï köuka, on the other hand, just irresistible to pukeko. Bar chart data Mark Kimberley
Survival appeared to be the biggest challenge.

The survival of open-ground plants, because their roots are exposed during transplantation, presents a particular risk.

But rather than the open-ground, the most vulnerable proved to be the root trainer –raised plants.

This trend, across the three trial sites, and like so many aspects of the open-ground project, and the method itself, is entirely counter-intuitive. Logic would have suggested that the less a plant’s root system was disturbed during transplantation, the less transplantation shock, and associated mortality, would be involved.

It is possible that in trials where plants were stringently free from competing grasses and other weeds, open-ground plants would exhibit a higher mortality than planter bag/potted or root trainer –raised plants. However it was decided, including for purely pragmatic reasons, that the plants would be exposed to a level of competition that was broadly typical of indigenous plant establishment projects—as opposed to best practices, which are often not achieved in projects such as those funded under the Mahurangi Action Plan.


Silverdale Terrace survival bar chart 2009Where Weeds Were Worst: The rich soil of the Silverdale river terrace initially grew the most vigorous crop of competing grasses, compared with the other two sites. This is possibly the reason the grasses harakeke and toetoe fared comparatively poorly.
Bar chart data Mark Kimberley
The particular vulnerability of root trainer plants is the ease with which they can be dislodged, particularly the smaller of the two sizes in common use, Hillsons, which are used in the trial.

At Sandspit Road, tï köuka (cabbage tree) is vastly over-represented in the plants recorded as missing or dead.

Tï köuka roots are known to be of particularly interest to pükeko, suggesting that the indigenous swamp hen is the main culprit there. The trial situation whereby an entire row can consist of lightweight, root trainer tï köuka, and the adjacent wetland, must present unprecedented convenience for pükeko—illustrated by the pattern of greatest losses being contiguous and at the end of the row closest to the water.

In four of the six species, planter bag or potted plants (PB3-size) suffered negligible losses.

However only in three species did the open-ground plants boast negligible losses.

The one species that outperformed open-ground, over planter bag or potted plants, was karamü—it is known to strike very readily. But the difference over planter bag or potted (an average of a little less than six percent) was only statistically significant at the Silverdale Terrace site.


Silverdale Hillside survival bar chart 2009 All Downhill: Because competing grasses were initially light on the relatively infertile hillside site, plants were not released. Subsequent paspalum growth, falling downhill under its own weight, swamped the leaves of tï köuka and toetoe and is probably the cause of its higher mortality—stiffer harakeke leaves not as readily subdued.  Bar chart data Mark Kimberley
Open-ground and root trainer mänuka suffered uniformly large losses compared to 100% survival of the PB3-sized containers. This would appear to reflect the famous sensitivity of mänuka to having its root system disturbed.

The largest losses from a single species were of koromiko—open-ground fared worst, at 72.5%—probably the result of browsing by rabbits.

Given that the open-ground plants received no additional treatment aimed at reducing transplantation shock, the trial results showing them having comparable survival rates to planter bag or potted plants, and far superior to those of the Hillson-sized root trainers, are very positive.

Statistical significance

Biometrician Mark Kimberley has determined that the following results are statistically significant:
Sandspit Road spread bar chart 2009 Serious Sandspit Spread: Open-ground spread significantly exceeded all root trainer plants in all species, and planter bag/potted (although only significantly in the case of harakeke) in all but two species: Mänuka, with its famously finicky root system and tï köuka, inexplicably. Bar chart data Mark Kimberley


Sandspit Road spread bar chart 2009 Uneven on the Terrace: In spread, open-ground plants hold their own with planter bag/potted, and significantly surpass root trainer. The relatively poor showing of harakeke is possibly due to smothering a critical growth period. Bar chart data Mark Kimberley
Spread
The spread measurement is the average of the width of the foliage across is broadest axis, and the width of the axis at right angles to the first measurement.

While it is a broadly useful measurement within species, spread gives only a very rough comparison between species as different in form as toetoe and mänuka.

That said, toetoe was the standout, all the more impressive considering that little over 71% survived—when it is good, it is very, very good…



Sandspit Road spread bar chart 2009 More Even on the Hill: Although the pattern on the hillside site was more even than on the terrace it is unclear why harakeke, which is generally regarded as bombproof, open-ground, spread so much better at Sandspit Road than at Silverdale. Bar chart data Mark Kimberley

More measurements
It is clear that the trials should be measured at least once more, preferably before the spring growth surge in 2010.

This will determine whether significant mortality has resulted from the decision not to release in 2009, and whether the trend for open-ground to be greater in spread than planter bag/pot plants becomes statistically significant.




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