Site preparation is an essential prerequisite to seeding. The degree of preparation required depends on the weeds and animals present, but will be limited by site accessibility, timing, funds and the availability of labour.
Consideration should be given to what’s pragmatic and practical, and to what extent certain works (e.g. soil disturbance) may also encourage invasion by competitive weed species. Ongoing maintenance will improve the success rate of emerging native seedlings, and adequate resources must be allocated to achieve this.
As described on the Seed Islands page, concentrating seeding and subsequent maintenance activities in selected microsites is a much more effective use of time, money, resources and precious seed rather than trying to broadcast sparsely over a larger area.
Establishing communities of native species in these microsites encourages fruit-eating birds to the area, accelerates progress towards achieving canopy cover, and helps to create the right environment for subsequent seedings to spread.
To ensure maximum success, surveys of the site will need to be undertaken well in advance of seeding to locate the most favourable microsites for the chosen species. More information on how to select the right microsites is provided on the Seeds Islands page.
An assessment of the animals present, or likely to be present, is another essential prerequisite of any seeding programme. Animal exclusion is highly likely to aid in the success of the programme, and the extent to which animal control is required depends on what is present and which species are to be sown.
For example, hares and rabbits don’t tend to favour mānuka as much other native tree species, nor are rodents likely to eat the seed, and so if this is the only species being broadcast then the degree of animal control required may be minimal. However, hares and rabbits have the potential to completely decimate other palatable species. Deer, goats, wallabies, wild pigs and stock can also to do a lot of damage if present and are not controlled. A further complication of a seeding project is that rodents also need to be considered as they have the potential to attack the seed itself.
The method of animal control depends on what is being controlled, site accessibility, timing, funds and the availability of labour. If fencing is to be used, then consideration should be given to the long-term use of the site e.g. if there are aspirations to create an ecosanctuary one day, then it may be worth installing the necessary fencing now rather than installing a less-effective fence now and then having to replace it later.
Certain temporary fencing materials can be used to create a microclimate within the fenced area itself. For example, some protection against extremes of wind and frost can be provided in localised areas by using shade cloth along fence lines. Care must be taken not to make the fenced area too shaded though.
Native seedlings, like any other plant, need water, varying degrees of light and nutrients. Invasive weeds can reduce the chance of success by creating competition for, and reducing the availability of, these crucial ingredients for growth. Weeds can also cause smothering and overtopping of seedlings and can form dense cover on the forest floor preventing other seedlings from germinating. Neglecting to control weeds may result in failure of the entire seeding project, but effective control can result in faster and more sustained growth of native seedlings resulting in a much higher success rate.
Using appropriate herbicide is the quickest way to clear weeds in and around the selected microsite where the native seeds are to be sown. Weed-specific herbicides are safe to use if label instructions are followed and spray drift onto non-target plants is avoided. The residence time of the herbicide must be checked so that it doesn’t impact on the subsequent seeding operations. Weed spraying the site in late summer means that collected seed can be sown in autumn and doesn’t need to be stored over winter. Weed spraying in spring can delay sowing and means that the seed will need to be stored carefully over winter.
When weed spraying, it is advisable to spray a wider area than where the seed is to be sown so that the nearby seed source is removed and so that nearby rank grass and other taller weeds are less likely to collapse onto the seeding site and smother new seedlings. However, over-clearing is not recommended as this can make the site too exposed to pest animals, weed invasion and weather extremes. In certain parts of the country, some weeds such as gorse can actually be used as nursery plants as they are nitrogen fixers and provide shelter and protection against some pest animals.
Another way of removing weeds is through hand-pulling and screefing. This has the added advantage of clearing the area so that the seed, when sown, will come into contact with the soil quicker. However, this can also lead to an explosion of weeds because disturbed open sites are ideal for weed establishment, and so close monitoring and follow-up control will likely be required.
With any restoration project it is recommended to avoid over-clearing any area that can be dealt with in one year. Wilding control projects using herbicide tend to cover a much greater area than this, and so the fight against weeds will be ongoing until the native canopy has begun to form. This is another reason why efforts are best focused on microsites rather than trying to restore the whole site at once. The larger the area cleared, the more likely it is that a fast-establishing and hardy nursery crop will be required to help suppress weed invasion (see more on nursery crops on the Critical Success Factors page).
Wilding conifer control operations using herbicides tend to kill off anything beneath the wildings as well as the target wilding conifer trees, although work is currently being undertaken on more species-specific herbicides. There will be initial understory die-off when the herbicide is first applied, and there may be further die-off when the contaminated pine needles drop to the forest floor and start decaying. Depending on the herbicide used, no significant new growth would be expected on the forest floor in affected areas until any herbicide residue has attenuated, which may be anything from 6 – 24 months. There could be an opportunity at this point in time to introduce native seed in an attempt to establish native seedlings before invasive weed species take over the site. This is demonstrated schematically in the figure below.
The relationship between herbicide application, wilding decay and weed reinvasion
Taking advantage of this opportunity requires careful planning and close monitoring of the forest so that the optimal time for seeding (i.e. the “sweet spot”) is not missed. However, abundant, viable native seed may not be available every year. Ideally this would be planned as part of the initial wilding control operations so that seed can be collected and stored in advance where possible, bearing in mind that viability of many species does tend to diminish the longer the seed is stored.
Additional weed control will likely still be required even if the native seed is introduced before weeds reinvade. This is because wilding spray control operations don’t always kill 100% of the understory weeds, so there will be remnant patches of undesirable species which can spread quickly as the residual herbicide abates and decomposing wildings allow more light to penetrate through to the forest floor.
It is worth noting that simply killing weeds achieves little in terms of making the soil ecosystems suitable for native forest restoration. Furthermore, if the site is simply cleared of weeds without any associated native forest restoration efforts, then the weeds will return, resulting in an endless cycle of weed invasion and control. If large areas have been cleared, then it may be necessary to establish a quick-growing, hardy nursery crop to help suppress weed invasion and to help create the right conditions for the introduction of other native species (see more on nursery crops on the Critical Success Factors page). Establishing a closed canopy of native species may be an effective way to stop the wildings from reinvading (with the exception of Douglas fir due to its high shade tolerance).
Clearing away dead weeds, pine needles, leaves and other ground cover will ensure that broadcast seed is more likely to come into contact with the soil, and therefore more likely to germinate. Different methods may be employed depending on site accessibility, timing, funds and the availability of labour. Consideration should be given to what’s pragmatic and practical, and to what extent certain works undertaken (eg soil disturbance) may also encourage invasion by competitive weed species.
Simply raking away the ground cover or removing dense grass swards by screefing will increase the success rate, although these methods are not particularly upscaleable without a large workforce. Once again, concentrating activities to achieve good results in selected microsites is a much more effective use of time and money rather than diluting efforts across a whole hillside. Ongoing maintenance will improve the success rate of emerging native seedlings and adequate resources must be allocated to achieve this.