More than 1.2 million trees are being planted, one for each household in the State, to mark the millennium.
Every household should receive a certificate by post in the coming weeks, pinpointing in which of 14 designated forests their tree is planted. It will give the number of the tree and its location.
The £5 million project, "The People's Millennium Forests", is the biggest attempt to restore Irish woodlands with native broadleaf species. The designated 1,500 acres include forests that are being extended, and native woodlands under threat of extinction, will be replanted. Species include oak, ash, birch, alder, hazel, yew and Scots pine.
The chosen forests are Ballygannon wood, Rathdrum, Co Wicklow; Shelton Abbey, Arklow, Co Wicklow; Camolin Park, Enniscorthy, Co Wexford,; Lacca, Mountrath, Co Laois; Coill an Fhaltaigh, Kilkenny; Glengarra, Cahir, Co Tipperary; Muckross, Killarney, Co Kerry; Rossacroo-na-loo, Kilgarvan, Co Kerry; Portlick, Athlone, Co Westmeath; Rosturra, Loughrea, Co Galway; Derrygill, Loughrea, Co Galway; Tourmakeady Wood, Tourmakeady, Co Mayo; Cullen tra, Sligo, and Derrygorry, Monaghan.
Presenting certificates to families representing 19 counties on Monday (the remaining seven were deterred by the weather), the Taoiseach Mr Ahern said: "It is a lasting millennium legacy that will be a source of enjoyment and inspiration for present and future generations well into this new millennium."
The project is sponsored by the National Millennium Committee and AIB, and managed by Coillte in partnership with the Woodlands of Ireland Group. It is supported by a number of other environmental organisations.
Certificates are being issued to households on the 2000 electoral register but are also available to those not on the register or without a fixed address. The certificate is also available in Irish on request.
A nationwide awareness campaign will include a roadshow, schools' programmes, video and other promotional material.
An information line has been set up - 1 850 248 848 - and is open from 9 a.m. to 6 p.m. Monday to Friday, charged at local rates. Or consult the website: www.millenniumforests.com