Obviously, sand dunes must stabilize (stop growing and moving) to some degree before vegetation can take hold. So it would have to have been after Bayocean started shrinking, as discussed in Pre-historic Geomorphology of Bayocean Peninsula.
Photos taken when the town was being built show trees; and sales brochures featured them. In Coastal Sand Dunes of Oregon and Washington, William Cooper noted that when he visited Bayocean Park in 1928 it was "fairly well covered with brush and grass, and there were a few young pines and spruces upon it."
|190 rings on a 38" diameter log along Dike Road|
At the other end of the spectrum, the natural ecological cycle has brought trees back to the southern dunes of Bayocean more recently. Photos taken by Bert and Margie Webber, and published in their Bayocean: The Oregon Town that Fell Into the Sea , show dunes covered with grasses and Scotch broom, but no trees. If the photos were taken before the original 1989 edition, the shore pine and shrubs present today are less than 36 years old in 2015. If the photos were taken just prior to the book's 1992 revisions, the trees are less than 23 years old. It's nice to see young'uns when admiring the old timers.