The dendrochronological scale of bristlecone pines extends back nearly 9000 years. Trees in the same area share bountiful and lean years which result in wide or narrow rings, respectively. Dendrochronology is useful to about 8000 years before the present. Trunks of dead bristlecone pines have been matched to live ones, creating a scale which extends back about 9000 years before the present. Creationists argue that trees can grow multiple rings - or none at all.
Tree ring dating is complicated but very reliable when properly done.
The authors also have a 1600 year old pine chronology which overlaps the end of the oak chronology. As interspecies comparison is difficult they have not yet fixed an absolute age for the pine chronology. If they are able to we will probably have a chronology going back 11,500 years. This will cover the whole of the Younger Dryas with even better resolution than provided by ice cores.