Revegetation Techniques
There are three techniques that are commonly used for revegetation:
Natural regeneration is the term used to describe the growth of plants from seed naturally distributed to the site. Natural regeneration relies on existing seed sources, such as soil or canopy stored seed, or seed transported to the site by water, wind or animals in the area to be revegetated. This method of re-establishing vegetation is especially worthwhile for individuals and groups with limited resources. Natural regeneration is a good first choice, because native plants that grow from this method are likely to be well adapted to the site. If there is a good source of seed, natural regeneration can result in high species diversity, representing the original range of plant species.
Although the process of regeneration itself is 'passive', natural regeneration still usually requires facilitation and management. The areas to be revegetated are usually fenced to exclude stock and allowed to regenerate naturally. Some form of pre-treatment, such as a burn or herbicide treatment, may be applied to the site. If the regeneration fails or is poor, direct seeding or planting seedlings can be considered. As with other methods, implementation of a long-term weed management strategy is important.
Direct seeding involves sowing seed directly into prepared ground. Direct seeding generally is more efficient in terms of time, cost and labour, compared to tubestock planting. It also allows for a more diverse seed mix, leading to greater plant diversity. The main limitation with direct seeding is usually the availability of seed. Establishment of plants from direct seeding can be patchy and can take several years, especially for hard-seeded species, but the plants that do establish are often robust and have developed a good root system. There are two main methods of direct seeding:
- tubestock planting,
- direct seeding
- natural or assisted regeneration.
Natural regeneration is the term used to describe the growth of plants from seed naturally distributed to the site. Natural regeneration relies on existing seed sources, such as soil or canopy stored seed, or seed transported to the site by water, wind or animals in the area to be revegetated. This method of re-establishing vegetation is especially worthwhile for individuals and groups with limited resources. Natural regeneration is a good first choice, because native plants that grow from this method are likely to be well adapted to the site. If there is a good source of seed, natural regeneration can result in high species diversity, representing the original range of plant species.
Although the process of regeneration itself is 'passive', natural regeneration still usually requires facilitation and management. The areas to be revegetated are usually fenced to exclude stock and allowed to regenerate naturally. Some form of pre-treatment, such as a burn or herbicide treatment, may be applied to the site. If the regeneration fails or is poor, direct seeding or planting seedlings can be considered. As with other methods, implementation of a long-term weed management strategy is important.
Direct seeding involves sowing seed directly into prepared ground. Direct seeding generally is more efficient in terms of time, cost and labour, compared to tubestock planting. It also allows for a more diverse seed mix, leading to greater plant diversity. The main limitation with direct seeding is usually the availability of seed. Establishment of plants from direct seeding can be patchy and can take several years, especially for hard-seeded species, but the plants that do establish are often robust and have developed a good root system. There are two main methods of direct seeding:
- Hand Sowing: this method is useful for small areas or in inaccessible country. Handfuls of seed mixed with a bulking agent are thrown onto the prepared seed bed. Another method of hand-seeding uses cut stems of a plant with ripe fruit present, laid across a prepared site.
- Mechanical direct seeding: this method involves the use of specialised direct seeding equipment, which is calibrated for different seed sizes and planting depths. Large areas can be seeded quickly using this method - up to 50 hectares in one day using one direct seeder.
'Tubestock' is the term for seedlings that have been raised in small nursery tubes, for transport to the planting site. Propagation of seedlings can be by seed, by cuttings, or through division. Seedlings can be planted by hand or with a mechanical seedling planter at the prepared site. As with direct seeding, site preparation is essential and will involve weed control and fencing.
Even though tubestock planting is more expensive and requires more labour than direct seeding and natural regeneration, it is a widely used method of revegetation. Results are reliable and immediate, and plant placement is controllable. Because of the labour-intensive nature of tubestock planting (both in propagation and planting), fewer species tend to be planted than with direct seeding.
Specifications for healthy tubestock
Healthy seedlings of sufficent size are crucial to successful tree planting. Seedlings need to have healthy roots that are ready to grow as soon as they come into contact with the soil, so as they can establish a permanent water supply and not be reliant on supplementary watering. The shoot should have healthy leaves that can begin to provide the energy the plant needs for growth through photosynthesis. The ratio of the shoot to the root is important. Too big a shoot:root ratio means the root system is unlikely to provide enough water to support the shoot and the plant will be top heavy. Too small a shoot:root ratio and the leaves will not be able to provide enough energy for the roots to grow. Ideally a shoot:root ratio between 1 and 3 is ideal. Roots should not be circling in the pot. Plants with circling roots can "strangle" themselves in the field many years after planting, and growth is nearly always slower. Roots should also not be protruding from the sides or base of the pot. Modern nursery practices encourage air-pruning of roots as soon as they protrude from the pot. Any protruding roots should be cut off with a clean pair of secateurs before planting. Avoid plants with very thick roots protruding.
Seedlings should be hardened off to suit the conditions they will be established into. Nurseries provide an artificially benign environment for young plants to grow in. Unless plants are hardened, they will suffer transplant shock and are likely to die. Heat and frost are the conditions that plants must be most prepared for. Before planting, seedlings should be stored in the open, where they will experience temperatures closer to what they will experience after planting.
When seedlings are grown close together, as in trays or tubes stored close together, they usually only have leaves on the top third of the shoot. This will not affect growth if the plants are not too tall or if the shoot:root ratio is less than 3. Tall seedlings with only a few leaves at the top should be avoided.
Healthy seedlings of sufficent size are crucial to successful tree planting. Seedlings need to have healthy roots that are ready to grow as soon as they come into contact with the soil, so as they can establish a permanent water supply and not be reliant on supplementary watering. The shoot should have healthy leaves that can begin to provide the energy the plant needs for growth through photosynthesis. The ratio of the shoot to the root is important. Too big a shoot:root ratio means the root system is unlikely to provide enough water to support the shoot and the plant will be top heavy. Too small a shoot:root ratio and the leaves will not be able to provide enough energy for the roots to grow. Ideally a shoot:root ratio between 1 and 3 is ideal. Roots should not be circling in the pot. Plants with circling roots can "strangle" themselves in the field many years after planting, and growth is nearly always slower. Roots should also not be protruding from the sides or base of the pot. Modern nursery practices encourage air-pruning of roots as soon as they protrude from the pot. Any protruding roots should be cut off with a clean pair of secateurs before planting. Avoid plants with very thick roots protruding.
Seedlings should be hardened off to suit the conditions they will be established into. Nurseries provide an artificially benign environment for young plants to grow in. Unless plants are hardened, they will suffer transplant shock and are likely to die. Heat and frost are the conditions that plants must be most prepared for. Before planting, seedlings should be stored in the open, where they will experience temperatures closer to what they will experience after planting.
When seedlings are grown close together, as in trays or tubes stored close together, they usually only have leaves on the top third of the shoot. This will not affect growth if the plants are not too tall or if the shoot:root ratio is less than 3. Tall seedlings with only a few leaves at the top should be avoided.