To quote Doran's complete description (items in [square brackets] are mine):
Among the simplest, and presumably most ancient, types of watercraft in Austronesia are boats made of bark. The simplest of all are formed of bark sheets plugged at the ends with clay [top image], whereas others are tied at the ends [center] and more complex ones have sewed ends [bottom]. The principle location [i.e., within Austronesia] of bark canoes is Australia, but a few relicts are found in Indonesia, probably indicating a much wider distribution.The sewn canoe shown differs from those of Arafura not only in the shape of the end but, significantly, in its having gunwale members lashed to the sheerline. The Arafura boats were entirely without added structural members.
The very simple bark rafts of the Tasmanians allowed some mobility on the water but became waterlogged in about six hours and were never used for distances offshore greater than about eight miles.
Although Doran says that bark canoes were "Among the simplest, and presumably most ancient types of watercraft" (emphasis added), he is not implying that they are the simplest or most ancient. That distinction he applies to log rafts, noting that true rafts rely on the inherent buoyancy of their material of construction, rather than on a designed, built structure that displaces water. Also in support of his argument: it is a simpler matter to tie one floating log to another, thus creating a raft without any tools at all, whereas even the simplest bark canoe requires tools of some sort to strip the bark from the tree.
Doran shows the distribution of the various types of bark canoes in the following map, along with the distribution of dugout-based outrigger canoes with constituted the focus of his study.