Where were oak savannas and woodlands? How do you know?

Where and when did this ecosystem exist?

How do you know what the landscape was like anyhow, now that it is altered so drastically?

These two types of oak habitat may have occupied up to 900,000 acres in the Willamette valley alone, before European settlement. It is generally accepted that 20% of the oak woodlands and savannas that were here when Europeans settled the valley are still around – mostly on private land.

We know this because botanists have examined General Land Office surveys of the valley from 1851 – 1910. These surveys recorded remarkably detailed information on vegetation along survey lines. The reconstruction is an approximation, since the records don’t include the vegetation inside the section lines, but it gives a pretty good idea of how the valley looked when Europeans arrived. The landscape was a “mosaic” of vegetation types: the most abundant, and now the most rare (only about 1% of these unique habitats remain) were prairies. Wet prairies and drier upland prairies were places where a diversity of grasses, sedges, and herbaceous plants grew. Besides savanna and woodland, conifer forest grew at higher elevations, and forests of deciduous trees lined the rivers.