Establishing and managing hardwood plantations
Successful plantation establishment depends on:
- appropriate site preparation
- early and maintained weed management
- early fertiliser treatment
- watering in (when required).
The appropriate stocking rate (planting density) promotes optimum growth rates and efficient plantation management.
The recommended tree planting design is 4m between rows and 2.5m between trees, giving an initial stocking rate (planting density) of 1,000 trees per hectare. This density encourages the canopy to close rapidly, reducing weed problems and improving tree form and branching. This population density is high enough to allow trees with exceptional form and vigour to be selected to carry-through as the final sawlog crop.
Site cultivation and planting
Generally, increasing the level of site cultivation will result in increased tree growth and survival. Site cultivation depends on the degree of slope and level of soil compaction. Before cultivating, it is important to reduce the existing biomass (plant cover) by slashing, burning or disc cultivating. This will improve machinery access and effective soil cultivation.
Deep ripping (prior to cultivation) may be useful to improve soil drainage and root penetration on compacted sites with clay subsoil. However, deep ripping should only be done when really necessary, as it increases the risk of erosion on susceptible soil types and can increase establishment costs.
Ripping in winter or spring is recommended, when soils have optimum moisture levels for penetration and shattering. On dry sites, ripping should be done on the contour to increase moisture infiltration for tree use. On waterlogged sites, ripping should be done across the contour to encourage drainage, unless subsequent erosion is likely. Be aware that heavy machinery can cause soil compaction on wet sites.
- On highly compacted areas (e.g. former grazing lands), deep ripping to 60cm and soil cultivation (30-45cm) is recommended.
- On less compacted areas (e.g. former forest or plantation lands), soil cultivation to 30cm is adequate.
- On slopes of 0-15°, where water run-off is minimal and the soil type is not susceptible to erosion, strip cultivation is the cheapest and preferable technique.
- On slopes of 15-20°, or in areas where soils are easily eroded, spot cultivation is recommended.
Cultivation provides a better soil tilth for planting and can be achieved with a wide range of tools, including offset discs, rotary hoes and disc cultivators. Cultivation should be planned for when the soil is not too wet, avoiding soil compaction and damage to soil structure. Cultivate well ahead of planting to allow the soil to settle.
Mounding improves soil drainage and tilth. It can be beneficial to early growth and tree survival on most sites, particularly those that are waterlogged. Mounding improves diameter growth in trees by 54% on poorly drained soils. Mounds are generally constructed as part of the initial cultivation process and involve the use of specialised disc ploughs, which create a suitable mound in either one or two passes.
Build mounds along planting lines to at least 0.5m high and 1m wide. Construct mounds well ahead of planting to allow the soil to settle, reduce air content and therefore increase tree survival. Early weed control or mulching can be done in conjunction with mounding.
Adding gypsum while the trees are young will assist tree establishment on clay soils with poor drainage, waterlogging or high pH levels. This improves soil structure and permeability, root penetration and is particularly useful on sites with a hardpan clay subsoil and cracking clay soils.
For excessively acidic soils, incorporating lime or dolomite into the topsoil layers will raise soil pH. For highly alkaline soils, applying sulphate of ammonia will reduce soil pH in the top layer of soil.
Learn more about soil characteristics for plantation forests.
Competition from weeds severely reduces early tree performance, and weed growth can be prolific in sub-tropical and tropical regions. Controlling weeds prior to planting and maintaining control for at least 12 months is considered essential for successful plantation establishment. Establish a 2m-wide weed-free strip along each planting row during the first 2 years.
Fast-growing eucalypt plantations respond well to fertiliser application, and nitrogen (N) and phosphorous (P) have the greatest impact on growth. Where soils are already fertile, fertiliser application has less effect than on poorer soils. Generally, a fertiliser containing nitrogen (N) and phosphorous (P) should be used in a split application over 2 years.
Learn how to identify nutrient deficiencies in trees.
Although expensive and often difficult to conduct, watering-in is useful when soil moisture conditions are limiting. Watering-in extends the planting window and increases tree survival rates significantly.
Nursery trials have identified some drought conditioning techniques that significantly reduce the susceptibility of seedlings to low water availability after planting. Drought conditioned stock are hardier and should not require watering-in, except in extreme conditions.