Using poroporo as a nurse crop

Mt Chocolate is being used for a great big experiment to find faster and cheaper ways to establish native forest. Since mid-2017, different ways to propagate, plant and maintain native plants have been tried out.

Some ideas have worked and some have failed and lots of lessons learned. But each year the methods have been tweaked and progress is being made.

One series of experiments have been underway to find out if poroporo could work as a cheap and reliable nurse crop. A nurse crop is a bit like a scab. When you cut your finger, a scab helps with the healing but is only temporary.

Mike was told repeatedly by many people who plant natives that using poroporo would never work. In fact, it can work really well, but only if the right technique is used.

Mike has found out that poroporo can be used a bit like gorse, to provide shade from the sun and shelter from the wind for small native trees to get established. The idea came from learning from Hugh Wilson of Hinewai fame who is an advocate for using gorse as a nurse crop in certain situations.

It took a lot of trial and error to learn how to propagate poroporo correctly with careful seed treatment, sowing and then very specific planting methods. There were lots of failures involving around 5 litres of seed over the last 3 years.

The jury is still out on site preparation. Poroporo like warm soil in summer, and lots of shady weeds around its roots once it emerges up to the sun. 5-6 trials have been underway this summer to refine the existing technique to optimise success.

Winter at Mt Chocolate can mean frosts which damage poroporo plants. The roots are frost-sensitive and plenty of weeds, grass or mulch around the base of each poroporo is required by end of May.

Shade-loving trees and ferns are then planted under the poroporo, and poroporo can also be planted between trees that don't mind a bit of shade. Spacing and timing seem to make a big difference.

In the most successful test plots, within 12 months from the planting of poroporo, shade and soil moisture levels in summer are allowing for moss and ferns like "common pig fern" (Hypolepis ambigua) and Blechnum to self-establish  No lichens have been found yet on branches.

In the most successful plot of all, the poroporo bushes are 1 year old, 3m tall and ideal ground conditions have been created.  In other plots, poroporo plants might be 3 years old and only 1.5m high. The main problem here was plant spacing too far apart. Spacing too close has also led to poor results.

Regeneration is now kicking in with small seedlings emerging including native and weed species. Here are some photos of native trees emerging out of poroporo at Mt Chocolate.

450 poroporo were planted this summer. 2000 native trees and grasses will be going in this winter. Nursery production will then start to scale down with the emphasis on variety of niche species rather than bulk numbers of a few species.