The Rim Fire. The Ferguson Fire. These and many others cause us to look and say “why?” Is it climate change? Fire suppression? Too little logging? Good answers require a broader perspective than just the trees and just the time since the last fire. Just what has gone on in the Sierra Nevada?

First note that none of European descent ever laid eyes on truly pristine wilderness–lands untouched by human activity. As those who study recent prehistory have recognized for a long time, and as many land managers now also grasp, Native Americans managed much of the landscapes we today mistake for purely natural ones. Between setting frequent small fires and planting and cultivating some species, Native peoples built the forest we now see turning to ash before our eyes. To figure out how to nurture and protect that forest, we need to understand the changes they made to a purely natural environment.

So what did fires look like before the native peoples of California started to manage forests? You might hope that records in meadows and lakebeds from the past few thousand years might give a clear answer, but there is another layer of human intervention that sits beneath the more obvious burning and cultivation, and that layer clouds the view of what the forest would become if we left it alone. The modern forests emerged from the depths of the last Ice Age fully accompanied by human presence. What is more, that forest had a whole different set of inhabitants than previous iterations: cave bears and mastodons, saber-toothed cats and giant sloths and other large  animals vanished from the earth as the ice was retreating. What did their presence mean for the health of the last truly wild forests of the Sierra?

We know that modern ecosystems have not fully adjusted to the disappearance of the large animals some 10,000 years ago.  We see obvious “evolutionary anachronisms”–antelope that run far far faster than any modern predator, Osage oranges that are not eaten by any animal roaming North America.  More complex impacts are still to be found.  African forests are greatly changed by the paths made by elephants–did American mastodons and mammoths provide a similar service? Did some of these animals clear the forest floors of flammable plants?

Like it or not, we are the stewards of the natural world, and our choices determine the fate of the forests and landscapes under our care. We can blithely stumble forward, trying forest thinning or controlled burns or letting naturally ignited fires burn and see what we like.  But if we don’t understand how we came to inherit the forests we have–if we can’t untangle processes that created the forests in the first place from all the things we as a species have done to this natural system, then stumble we will.  As the climate does change we will need to understand the ecosystem well enough to not only adjust for past changes but to anticipate the new ones, and that is only possible with the broadest of perspectives, one reaching back in time farther than the written record or the oral histories that remain.  When Yosemite burns, it means we have not yet gained the necessary perspective, and so it should encourage us to redouble efforts to know the deeper history of its forest.


 Craig H. Jones is Professor of Geological Sciences and Fellow with the Cooperative Institute for Research in Environmental Sciences at the University of Colorado Boulder. His book The Mountains That Remade America: How Sierra Nevada Geology Impacts Modern Life was published by University of California Press in 2017.