Boolong tree

"This is because we need the Mountain air and the Boolong trees to thrive."

- Merin, explaining the dwindling Kin newborns.

The Boolong tree is a stubby, evergreen tree that grows thickly throughout Dread Mountain. Their trunks and branches are covered in thick, sharp thorns that make passing through thick growths of them almost impossible. The tree's bark is impenetrable by the thorns and can be used as a shield.

Kin, creatures native to Dread Mountain, possess thick hides the thorns cannot penetrate and simply shove the thorny branches out of the way to feed on the seeds in the cones of the trees. This feeding makes natural paths through the mountain forest that travellers can use to pass without harm.

The Kin and the Boolong trees seem to possess a symbiotic relationship, as the Kin need to feed on the Boolong cones to begin their breeding cycle and presumably, the seeds from the cones are spread and fertilised by their droppings, allowing the trees to spread and grow.

Secrets of Deltora
Doran mentioned boolong trees in his book, Secrets of Deltora.

Dread Mountain
Upon returning to Dread Mountain with Lief, Barda, and Jasmine, Bruna, Merin, and Ailsa descended into a thicket of Boolong Trees to avoid fire from the Dread Gnomes. After depositing the companions, the three Kin stuffed their pouches full of Boolong cones to share with their friends back at the Dreaming Spring.

After Prin joined the companions at the mountain, she helped to clear a path for them through the Boolong trees. At a gnome rest, the companions used pieces of Boolong trees as shields to protect themselves from the Dread Gnomes arrows.

After the death of the Ooze Toad Gellick, who had been supplying the Shadow Lord with venom for its Grey Guard's blisters, the Dread Gnomes created fake blisters by mixing Boolong tree sap with water. They also gave the companions an arrow made of Boolong bark as a way of summoning the Dread Gnomes whenever they should need their help.

Dragon's Nest
Lief read a letter from the Dread Gnomes' leader, Fa-Glin, on the night of the full moon meeting. In it, Fa-Glin told about the lack of food on Dread Mountain, and lamented that the gnomes couldn't eat the Boolong trees like the Kin.