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Natural Regeneration in Irish Woodlands: Seed Production

Natural Regeneration in Irish Woodlands: Seed Production

Kevin O'Connell discusses the process of natural regeneration of trees and woodlands from seeds produced and germinated on site, focusing on four key principles: seed production, seed predation, germination, and establishment, and details factors influencing seed production such as tree age and size

Natural regeneration can be described as the establishment of trees and woodland from seed produced and germinated in situ (Harmer & Kerr, 1995).  Four important principles govern the fascinating process of natural regeneration: seed production, seed predation, germination and establishment (Harmer, 1994). Over a series of four articles, Teagasc Forestry Advisor Kevin O’Connell will delve further into each of these principals in turn.

Seed Production

Seed production can depend on many factors including age and size of tree, light conditions and climatic conditions. The period of a tree’s life when the best seed is produced has been defined by various authorities as during middle age or 10 to 20 years after principal height growth has been completed (James, 1989). According to Aldhous (1975), the age of the first good seed year for ash is 25-30 years, for beech 50-60 years and for oak species 40-50 years.  Subsequently, the age of maximum seed production is 40-60 years for ash, 80-200 years for beech and 80-200 years for oak species.  The interval between good seed crops is generally 3-7 years for ash, 5-10 years for beech and 2-5 years for oak.  The quantity of seed produced can vary with the height and the size of the trees’ crown.  Generally the taller the tree and the wider its crown spread relative to other trees, the higher its seed yield capacity (Anderson, 1953).  There must also be an adequate light supply to the tree crowns before flowers will form and seed develop.  Dominant and co-dominant trees, occupying the greatest heights in the canopy, produce the most seed in woodland.  Anderson (1953) gives broad figures for the probable number of seeds produced per hectare, based on continental figures.  Oak is estimated to produce from 29,400 to 441,000 seed per hectare, beech from 171,500 to 2,450,000 per hectare and ash from 294,000,000 to 392,000,000 per hectare. These figures are likely lower in Ireland due to the infrequency of mast years.

Flowering and fruiting take place only when trees have passed through their juvenile stage (Anderson, 1953, Matthews, 1963).  The juvenile period can vary both between species and within species depending on such factors as the climate, the health of the tree and its location.  Very old trees produce very few viable seeds.  Trees can produce an abundance of seed if they are under stress or close to death.  Open grown or edge trees in a woodland tend to flower earlier and more consistently.  Once trees reach reproductive maturity, climatic conditions play an important part in seed production.  Most of the trees in our woodlands are dependent on wind for flower pollination.  If conditions in spring are damp, with little to no wind, then pollination will be reduced.  Conversely, too much wind in spring can break off new flowers.  It is therefore important for seed production that the weather conditions are just right at the time of flowering and pollinating (Anderson, 1953).

The proportion of male to female flowers is also important to ensure pollination (Savill, 1991). Oak and beech are monoecious; each tree contains both male and female flowers.  Ash can either be monoecious or dioecious (i.e. has only one type of flower on a given tree).  In some instances the quantity of seed may be small even if climatic conditions are right due to a disproportion between male and female flowers (Anderson, 1953).

The mobility and dispersal of seed can vary with species and site (Blackstock, 2006). In open conditions, light windborne seed such as birch and willow can travel for over a 100 metres; heavy wind-borne seeds of ash and sycamore travel in the order of tens of metres (Harmer & Kerr, 1995).  Mobility can be greatly reduced within a forest stand.  Heavy seeds like beech and oak are mainly dispersed by mammals, birds, gravity and generally remain close to the mother tree (Anderson, 1953). In summary, there are many elements at play between flowering and subsequent germination of viable seed in a woodland.


Aldhous, J.R. (1975) Nursery Practice, Forestry Commission, HMSO, London
Anderson, M.L. (1953) Prerequisites for Natural Seeding, Quarterly Journal of Forestry No.47, pp159 -169
Blackstock, P (2006) Natural Regeneration, presentation given at the native woodland course June2006, Forest Service
Harmer, R. (1994) Natural Regeneration of Broadleaved Trees in Britain: I Historical Aspects, Forestry Vol.67 No3
James, N.D.G (1989) Foresters Companion, Blackwell Press, Oxford
Matthews, J.D. (1963) Factors Affecting the Production of Seed by Forest Trees, forestry abstracts 24 i- xiii
Savill, P.S. (1991) The Silviculture of Trees used in British Forestry, Rowe, Chippenham