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Direct seeding in New Zealand.
 Aerial seeding of pasture grasses was developed in the mid 1940’s and direct seeding of trees was utilised extensively during the early 1960’s.

During this time the Forest Service used wide scale seeding by to control the severe erosion on the Hawkes Bay side of the Ruahine and Kaweka ranges. This had impressive but controversial results. Pinus contorta was the species sown by helicopter on bare and seriously eroding mountain slopes but by the late 1970’s it was decided this prolific seeding exotic pine was an invasive weed due to its capability of growing above the native treeline. However it did solve the erosion problem and clearly demonstrates the huge power of direct seeding and selecting appropriate native species.

Over the years direct seeding has not found a lot of favor with the large scale tree planting in this country  because in forestry plant spacing is important and cloned material or superior genetic seed is in short supply and more suited to container culture. Using native plants for rehabilitation of damaged sites is a new idea that has emerged in the last decade. Planting of native trees to date has used a transplant system the same as the one developed for forestry. Most of these plantings have grown and all of them have cost very large sums of money to establish (a minimum of $20-30,000 per ha). Various methods have been tried with direct seeding natives including hydroseeding, fabric seeding and pelleting seed. In most cases its worked more or less. A very low rate of seed which is not very viable (rather than the application method) is the most likely reason for failures. Getting good viable native seed can be difficult but with the involvement of experienced plantsman totally achievable. Direct sowing specially selected species dry is easy, fast and closely mimics what happens in nature (where there is no need for fancy expensive polymas or fabric). 

Plants sown from seed have some huge advantages apart from costing far less.  The plants have no weeds, insects or diseases brought in with them and this is what makes it scientifically interesting and desirable to direct seed as opposed to planting trees. Direct seeding is especially useful on sites where it is doubtful that tree planting in the conventional way is worth the effort or where tree planting is not working or practical for any reason.

Direct seeding is highly suitable for barren sites such as those created from mining  or roading. Sites which have been recently disturbed and have no (or few) weeds present and/or no weedy top soil work best. However, techniques have been developed to adapt direct seeding to weed infested fertile low land sites as well. In Northland, fertile pasture has been successfully seeded even in the presence of severe weeds which normally make even tree planting a real challange. Here the soil has been turned using giant disks behind a crawler tractor and clean seed has been applyed to the exposed subsoil.

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Disking and sowing in weedy conditions
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Regrowth on the same site 4 yrs later

 

Successful direct seeding depends on:

  • Choosing the correct species for the site, region and purpose
  • Obtaining high quality viable seed (correct cleaning and treating)
  • Sowing at the right time
  • Controlling pests

Advantages

  • Rapid and cheap revegetation of desired areas
  • Seed is easier and cheaper to transport and store than seedlings. 
  • A greater range of species can generally be established than with planted nursery stock
  • Direct seeded plants tend to have better root growth and are therefore more prepared for climatic extremes
  • Less disturbance of site to generate weeds

Disadvantages of direct seeding include:

  • Difficult to get the seed, training and labour is required.
  • Direct seeding is not as suited to weathered steep surfaces or certain non-wetting or heavy textured soils that can have problems with surface drying and sealing. Recently disturbed ground has the best result.
  • There is a low survival of viable seed – lots of seed is required
  • It often takes 9 to 12 months to see the results of a direct seeding project as plants are small and slow at first.
  • Requires a great deal of background knowledge or training.
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Bushman inspects 6 yr old direct seeded Manuka