Tree coverage in Ireland was at its lowest point a century ago. The
EU has nothing to do with it. In fact, Irish tree coverage has been
slowly growing since the 70s. The trees disappeared for farming, fuel
and for building (including ships), centuries ago.
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I'm confused as to why you would take the fictional series "Last of the
Summer Wine" as a guide. However the fields in the area it was filmed in
are grazed by sheep.

In the British uplands grazing by sheep and deer prevents regeneration
of forest. Where grazers have been excluded (e.g. Coire Ardair,
Abernethy Forest) regeneration is occurring.

In the lowlands the great majority of fertile land is used for
agriculture.


(Forest growth may well be slower in Britain; it's a lot further north
than the mid-Atlantic states - remember it's at the latitude of
Labrador.)
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OK. I understand. Thanks to all for your responses.