Raising young trees in large-scale forest nurseries is a first stage in providing the new seedlings for establishing or re-populating woodlands.
The forest nursery aims to produce good quality plants in uniform batches and as cheaply as possible. By good quality, foresters mean a sturdy plant with a well-balanced root and shoot and a well-developed root system.
The first step is to treat the seeds if necessary and sow them out on prepared seed beds to give maximum germination and early growth. Seedlings are then lifted when dormant (in winter) and transplanted into lines where they have enough but not too much space to grow into well-shaped plants to be planted out when ready.
For most trees, seeds and seedlings start life best in light acid soils such as sandy loams or even sands. Seed beds need good preparation.
The tiny seedlings are planted or lined out by machines in rows and at a density of about 100-150 plants per sq.m. They may need fertilising, irrigating, weeding and protecting.
Young forest seedlings need a good root system if they are to survive when planted out. Instead of transplanting seedlings from their original seed beds out into the nursery, their roots can be severed by drawing a sharpened steel blade through the seed bed at an appropriate depth. This undercutting cuts or prunes the main root and stimulates the growth of a branched and fibrous root system.
Most seedlings are planted as bare-rooted transplants raised from seed, spending one or two years in seed beds and then being transplanted for a further one to two years before being lifted and planted out in the forest. Transplants are described as 1+1, 2+2, 1+2 etc. depending on the years spent in the seed bed (the first number) and in the transplant lines (the second number). So a 2+2 spent two years in the seed beds and two in the transplant line.
Where the seedlings were left in the seed beds and undercut rather than transplanted, two and three-year-old undercut plants are referred to 1u1 and 1u1u1 in forestry nursery catalogues.
Larger seedling plants are not always the best to use; the biggest is not always best when it comes to seedlings. A healthy fibrous root system is often as important as the green parts seen above ground.
Besides the main method of seed beds and transplant lines in open ground nurseries, more and more seedlings are produced in small containers or cell-grown each year. Unlike bare-root nurseries, container nurseries are not confined to places with suitable soil types.
Vegetative propagation of trees from cuttings is becoming commoner and is normal practice for some species such as poplars, willows, London plane, Lawson cypress and Leyland cypress.
Producing the massive numbers of seedlings needed for afforestation work is a different ball-game from raising trees in pots to plant out in ones or twos in a garden. Forest nurseries work on large scale and low costs. They sell plants by the hundreds and thousands, not ones and twos.