Proving ‘open-ground’ worked would be the easy part.
The real challenge was always going to be to subsequently get anybody to take a blind bit of notice.
In particular, nurseries needed to be convinced to invest in the equipment and expertise required to raise indigenous species open-ground.
Transferring to Taupö, aside from ensuring a more focussed and robust trial, guaranteed that the work
would be noticed, given the high profile of the
Taupö Native Plant Nursery.
Fortunately for the initiative, a cornerstone of the
Sustainable Farming Fund’s approach is flexibility. Groups are urged to seek permission to change a project’s objectives, rather than persist down a particular path simply because that was the thinking encapsulated in the application.
The fresh approach permitted a more focussed and robust comparison of open-ground and container nursery methods.
The focus was now squarely on comparing how well the plants establish—with hindsight, this should have the first step in kick-starting the open-ground, forestry-style methods.
The economics of establishing indigenous species has to do with more than simply the cost of the plants. A much more useful measure is the cost of achieving canopy closure—the point at which the planted species are generally able to prevail in their competition with weeds.
Three methods compared
The three nursery raising methods are compared
- • Large containers—PB3-sized polythene planter bags or pots
- • Small containers—Hillson-sized root trainers
- • Open-ground.
PB3-sized planter bags and Hillson-sized root trainers are representative of the major container types commonly used for raising indigenous species.
Most indigenous revegetation species are raised in PB3 polythene planter bags or containers of similar size.
Root trainers are also a popular choice. These, by requiring less potting medium and space in the nursery are considerably cheaper than seedlings raised in pots or planter bags. Hillsons Rootrainers are the smaller of the two sizes in common use.
The open-ground technique being trialled is essentially that developed by the Forestry Research Institute in the 1960s and 1980s, adapted from the methods that have been standard practice for decades raising millions of radiata pine seedlings annually for the exotic forestry industry.
Six species trialled
Six indigenous species commonly used for restoration planting are trialled—three shrub hardwoods and three monocots. The three shrub hardwoods:
- • karamü—Coprosma robusta
- • koromiko—Hebe stricta
- • mänuka—Leptospermum scoparium
The three monocot species:
- • harakeke (flax)—Phormium tenax
- • tï köuka (cabbage tree)—Cordyline australis
- • toetoe—Cortaderia fulvida
More than three methods and six species could have been included. However, with the need for at least 100 individuals to be established, 18 combinations calls for a minimum of 1800 plants to be propagated. And that only provides sufficient plants for one trial site.
In the event, more than 21 000 plants were propagated, which subsequently allowed for three quite different trial sites to be established and for filler species trials.
Propagation
When the Forest Research Institute raised indigenous species open-ground, seed was first germinated in seed trays before being lined out—transplanted into rows in the open-ground nursery beds. In the Taupö trial, germination was performed in plug trays, which is now standard container nursery practice. It is also standard practice in forestry nursery for species that cannot be grown reliably from seed, as can radiata pine—one of the reasons it can be produced so comparatively cheaply.
Seed was mostly collected in the Mahurangi, in consideration of the establishment trials being located in that catchment. The balance of the seed was of Auckland regional provenance.
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The Open-Ground and Container-Raised Indigenous Plants Comparison is a Sustainable Farming Fund project.
Consistent Methods: Taupö Native Plant Nursery’s Philip Smith holding a Mahurangi karamü seedling ready to be transferred to an open-ground bed. Photographer Michael Bergin
Wide Open-Ground Opportunity: The trial might have transferred to Taupö, but the under-utilised land at the Ömaha wastewater treatment site could yet be deployed to produce millions of indigenous coastal plants, open-ground, to increase resilience to the inexorably rising sea level. Photographer Jonathan Barran