Moa may have been key to the spread of beech forests because they ate and spread native fungi essential for the trees’ growth.

A group from the University of Adelaide and Landcare Research in New Zealand studied fossilised moa dung from eight cave sites in Otago and northwest of Nelson.

In the dung of upland and giant moa, which were generalist browsers of the forest floor, they found the DNA of mycorrhizal fungi, a range of species of bright, truffle-like soil organisms critical for the healthy growth of beech forests.

Introduced mammals such as deer and possums eat both native and non-native fungal fruits and spread the spores in their dung—but native fungi don’t survive a trip through the mammalian gut. Rather, they evolved for the gentler gut of a bird.

Study author Alex Boast says the extinction of the moa may have affected the ability of the trees and their companion fungi to colonise new areas. Beech seeds need the right fungi in the soil, otherwise their expansion is limited to very slow growth outwards from the edges of existing forests.