A core turns depth into a sequence
A tree can disappear while some of its pollen remains in lake sediment. In a core, researchers examine samples at different depths and identify preserved pollen under a microscope. Dating supplies the connection between sediment depth and time. Without that chronology, a sequence of plant types would still lack a dependable calendar.
What happened at Chickaree Lake
A project summarized by the National Park Service used a sediment core from Chickaree Lake to examine vegetation and fire over about 2,500 years. Barrie Chileen identified 31 pollen types in 52 samples. Pollen represented plant communities, charcoal helped identify fires, and an existing radiocarbon chronology connected those observations through time.
Pine remained prominent, but the balance of pollen types shifted. The investigation could therefore ask about changes within a forest, rather than offering only a yes-or-no answer to whether trees existed.
Sources: s1
Do not turn a pollen list into a photograph
The National Park Service also describes pollen in Yellowstone lake sediments as evidence for changes in vegetation and climate. These are reconstructions from preserved material, not a complete visual inventory of every plant that stood beside a lake.
A botanical dossier for a proposed lost island would need to identify the actual core, its dating, the counted material and the reasoning linking those observations to a landscape. Where no core exists, regional ecology may constrain a fictional setting. It cannot supply a recovered pollen record.
Sources: s2