The most common trees are the leafy Atlantic trees that tend to form single-species forests (large beech forests) or mixed forests (made up of oak, beech, elm, lime, maple, ash, etc).

Large areas of the landscape are covered by beech forests. The most impressive ones are in the “Sierra de Aralar” and surrounding the nearby villages of Basaburua, the Ultzama and Leitzalarrea, to the north of Leitza. The undergrowth in the beech forests usually consists of bracken, holly and hawthorn. Large expanses of yew trees can be found in the Putxerri Nature Reserve.

Oak forests are less common but some magnificant examples can be found in Larraun, Basaburua and Ultzama (Orgi, in Lizaso). Together with the oak forests you can expect to find chestnuts, ashes, hazels, birches and limes amongst an undergrowth of hawthorn, Holly, sloes, bracken, heather and blackberry bushes. The other type of forest to be found in the region flanks the riverbanks. These forests are generally made up of willows, alders, ashes, poplars, hazels and elms. Given the predominate Atlantic climate it is surprising to find examples of typically Mediterranean vegetation mixed in amongst the other plants and trees (The Betelu Oak Grove which has been declared a Nature Enclave).