Did you know that blue oaks can be used to gauge rain? Daniel Griffin, Ph.D., at the University of Minnesota and his collaborators have found that the sizes of blue oak annual growth rings are highly correlated with annual precipitation. Dan is a dendroclimatologist, someone who determines past climates from the patterns in annual tree rings. Tree rings are wider when conditions are wetter and narrower when conditions are dryer. The patterns of ring widths in live trees can be correlated with known precipitation records to develop a statistical relationship that can then be projected back in time using ring-width patterns from old dead trees to look at past climates.
 

Using a long period of record developed from both living blue oaks and old dead blue oaks, some of which were collected from Tejon Ranch, Dan and his colleagues were able to estimate that the magnitude of the 2012-2014 California drought was greater than any such period in the last 1,200 years. To learn more about this exciting research, read this fivethirtyeight.com article.