Witness Trees Tell A Story

March 25, 2020

Witness Trees tell how ecosystems in Silicon Valley have changed.

As the land was divvied up, surveyors documented the trees that rested at the imaginary corners and angles of the parcels to mark their boundaries. They were called “witness trees” – an expression also used today for trees that were present at key events in American history like Civil War battles.

Witness trees are valuable tools for scientists studying ecosystem change, especially when they are long-lived native tree species.  One Coast live oak witness tree can help tie together archival data for a study area.  That tree may be documented not only in a 1925 U.S. Geological Survey, but also in a postcard from 1890, a Mexican land grant from 1861, and the diary of Spanish explorer from the 1770’s.  This data provide descriptions of physical features of the study area at different time points, which helps scientist describe how habitat in the study area has changed over time.

A new study by Erin B. Beller and colleagues scientifically tackles an important aspect of the story of our urban landscape: how do ecosystems change from the time prior to first permanent settlement to today, after growing into a densely developed modern city?   Click here, to read about this work.  The story was found on Envirobites.org, a website dedicated to explaining how cutting edge environmental research advances the understanding of our world.

U.S.G.S. surveyors

Surveyors in the field ca. 1925 working with an alidade and a plane table.  The alidade was used to sight an object and draw a line or angle on the plane table during the construction of a topographic map. (Photo courtesy of U.S. Geological Survey)