Scientists in my native state of California were handed a gift: a trove of detailed information about the state’s forests taken during the 1920s and 1930s and digitized over the past 15 years. When we compared this historical data – covering an area bigger than Great Britain – to current forests surveys, we found that California’s famed giant trees are suffering due to drier and warmer conditions.
This change to the forest landscape is important not only to the people of California. Large trees are huge sinks of carbon dioxide, provide habitat for many creatures and play a vital role in the water supply by, for example, providing catchment areas for snow. Forests that are denser with smaller trees are also more likely to burn.
Studying how the structure of forests is shifting over time provides us insight into how forests — a resource we depend on for many environmental and economic reasons — could change in a world of warmer temperatures.
Saved From Destruction
Researchers from the University of California at Berkeley and Davis, the Department of Forest Management at the University of Montana, and the US Geological Survey’s California Water Science Center worked together on a paper on California’s forests published last week in the Proceedings of the National Academy of Sciences.
The historical data for our study came from the Wieslander Vegetation Type Mapping (VTM) collection, which was created in the 1920s and 1930s. It’s been described in a 2000 paper as “the most important and comprehensive botanical map of a large area ever undertaken anywhere on the earth’s surface.”
This botanical map was pioneered by Albert Wieslander, an employee of the Forest Service Forest and Range Experiment Station in Berkeley, California. The collection consists of 18,000 detailed vegetation plots, over 200 vegetation maps, 3,100 photographs and hundreds of plant specimens. Overall, the collection covers about 280,000 square kilometers, or just over a third of the state. Combined, the data created a detailed picture of the state’s vegetation in the early 20th century — an important marker ecologists today can use for comparison.
During the 2000s, several groups, including my lab, launched efforts to digitize the plot data, maps and photograph portions of the collection. There still are some missing pieces. Indeed, the journey from paper collection to digital data has been a long one, with several cases in which documents were nearly destroyed either intentionally or by accident. It’s a cautionary tale about the importance of rescued and shared historical data in ecological and geographical analysis.
