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Direct Seed Revegetation

Finnsarby Place, Sumner Port Hills
Area: 6000m2 over Three Zones
Date: August 2016

 

Backstory

The objective was to remediate the landscape by restoring native flora to the sites that were no longer suitable for residential habitation after the Christchurch earthquake of 2011.

Finnsarby Place in Sumner, with a footprint of 6000m2, was substantial in terms of scale. Twelve residential houses were demolished.

Finnsarby is a high-profile site so it was important to LINZ that the revegetation blended with existing plantings for high aesthetic value.

Challenges

The three major challenges working this site were:

  • Maintenance of this scale without chemical herbicides
  • Gradients 1-1 to 1-3 with rope access methodology to secure coir matting and planting on the steepest slopes.
  • Degraded soil conditions due to compaction and lack of soil ecology within cut and fill zones, these areas can become swamped over winter and baked dry over summer Contract delivery of these projects requires quantifiable results equaling 90% plant survival. Any required replacements are at the contractor’s expense, which is a motivating factor to get it right. Our direct seeding initiative was insurance towards this end.

Since 2006, Red Tree has been observing direct seeding methodologies used across New Zealand and has noticed inconsistent results. There are three major reasons for these inconsistencies: lack of suitable germination environments, inappropriate maintenance methodology, and incorrect species selection.

The Solution

Our approach was to utilize our experience to create suitable germination conditions. Native seeds were dispersed at known ratios using appropriate seed blends then the area was covered with a bio-degradable erosion control matting that doubled as a seed germination blanket. Understanding the process of stratification which breaks seed dormancy is another crucial step in the process.

Traditionally, natives introduced by hydro-seeding methods are accompanied by fast germinating grass species which, can cause smothering as native seedlings have a slower germination time. Within the Finnsarby trial we omitted the introduction of grass species as a nurse crop and instead selectively managed the sites exotic weed species without the use of chemicals. Mechanical topping and manual releasing was our maintenance methodology with manually cut bio mass harnessed as a resource to establish mulch circles around emerging seedlings which effectively created micro-climates conducive for growth.

Our Outcome

Within the survey site the planted specimens have demonstrated slow to medium growth rates and native seedlings are in varying stages of establishment ranging from 10 to 50 cm in the nine- month period.

Survey Area: 340m2
Date: May 2017 9 months on
Planted Natives: 162 = 95% survival rate
Direct Seeding has yielded 123 plants
A total stocking of 258 plants
Delivering 168%