Successful establishment of trees depends upon a wide range of interacting factors including climate, soil, competing vegetation, pests and plant characteristics. The likelihood of successful establishment can be improved by appropriate cultivation, drainage, weed control, and correct species choice. Aspects that are increasingly recognised as contributing to good establishment are planting stock quality and seeding technique.
Historically much of the British and Irish uplands, below 600 metres, were covered by broadleaved woodland. Today, remaining areas of native woodland and scrub are mostly confined to narrow, steep-sided valleys in places where pressure from agriculture is sufficiently low to allow trees to re-establish.
Establishing trees and woodland on reclaimed land is a complex process which depends on the success of many activities. Allowing the wood to regenerate naturally can take many years, and should only be used where there is a reasonable diversity of shrubs and trees in, or close to, the site. Natural regeneration can be assisted by collecting tree seed from the local area, and sowing it on site.
Conventionally tree establishment has usually been achieved by tree planting, using tree stock grown from seed or cuttings in the nursery. Planting may be the best approach if there are no nearby sources of seed, or if only a limited range of species are present. Ideally, plants should have been grown from seed originating from wild trees in the same, or an adjacent, area. Chosen species should naturally occur in the area; these will be suited to the soil and local climate, and beneficial to local wildlife. However, alternative methods have been proposed and used in land reclamation, which involve the direct sowing of tree seed onto the site in question.
Compared to conventional tree planting, direct seeding is said to have a number of advantages:
- Tree seed of many species is comparatively inexpensive, and so woodland created from seed can be cheaper than using the equivalent nursery stock
- Growth from tree seed is more ecological and mimics nature more closely than artificial planting. Also, woodland emanating from seed is more natural looking
- Growth from tree seed results in rapid ground coverage and reduced herbicide use. Tree seeding and associated operations can be mechanised, using modified agricultural machinery
- Woodland created by seeding may be more robust, and gives more opportunities for selection of quality timber trees.
However, a disadvantage of this is seeding has a tendency to produce uncertain results, even if carried out according to best practice. The technique is prone to the effects of weather extremes, and seed depredation by some mammal and bird species.
Direct seeding, also referred to as direct sowing, is the process of sowing tree seed by hand or machine directly onto a seedbed in the final growing position for the woodland. Direct seeding is not always suitable on all types of substrate. Heavy textured, clayey soils, spoils that are subject to winter waterlogging and low-lying areas in the landscape should be avoided. However, these soils are often used for vegetation establishment on reclaimed land such as landfill sites.
To achieve sustainable woodland using direct seeding or conventional planting, the underlying substrate must be capable of allowing tree roots to penetrate and exploit the nutrients in the substrate. Direct seeding requires suitable soil preparation so that decompaction of the soil surface does not take place, and this can be carried out using complete cultivation or deep ripping, followed by rolling to re-compact the surface.
For successful establishment of woodland it is necessary to carry out the following operations:
- Seed pre-treatment
- Seedbed preparation
- Sowing at appropriate depth(s)
- Protection against mammal damage
- Weed control
- Thinning and re-spacing
- Monitoring and inspection.
Forest Research aims to increase the quality of commercially grown species and to ensure that stock of the most appropriate genetic origin is used in forest establishment. They are utilising new methods in biotechnology to deliver the products of its tree breeding to the industry and an appreciation of underlying genetic structures to policy-makers.
Edwards, C. (1998). Testing plant quality (PDF-131K). Forest Research, Farnham.
Forestry Commission (2006). Seed sources for planting native trees and shrubs in Scotland (PDF-995K). Forestry Commission, Scotland.
Gosling, P. (2007). Raising trees and shrubs from seed (PDF-648K). Practice Guide. Forest Research, Farnham.
Hutchings, T. (2002). The opportunities for woodland on contaminated land (PDF-1017K). Forest Research, Farnham.
Moffat, A. (2006). Tree seeding (PDF-1150K). Best Practice Guidance note for Land Reclamation. Forest Research, Farnham.
Willoughby, I., Jinks, R., Gosling, P. and Kerr, G. (2004). Creating new broadleaved woodlands by direct seeding (PDF-647K). Forestry Commission, Scotland.