The Dagshelgr Invocation was a custom practiced by the elves, in which they sang and performed planting spells. The influence of the Invocation was supposedly harmful to mortals. This also caused all creatures to find a mate, prompting Saphira's reflection of "I am alone", as there was no other known male dragon to her at that time other than Shruikan whom she swore she would not even consider as a mate.
This was the reason why Du Weldenvarden was filled with trees two to four times the size of normal trees found in other forests. Eragon, Orik, Arya, and their companions heard the elves perform this ceremony near Sílthrim. Arya cast a spell on Orik and Eragon to prevent them from being harmed by the magic of the ritual.