This is a clootie tree we came across near Leenane in Connemara. They are traditionally found near springs or wells and people often dip pieces of cloth in the water of the holy well and then tie them to a branch while saying a prayer to the spirit of the well. In modern times this is usually a saint but in pre-christian times it would have been a Goddess or local nature spirit.
This is most often done by those seeking healing, though some may do it simply to honour the spirit of the spring and it's a continuation of the old practice of leaving votive offerings to the Gods. It warms my heart to see an ancient Celtic practice still alive and well in this land.