What’s the deal with Yosemite’s dead trees?

One of the most frequently asked questions in my Yosemite workshops is some variation of, “Why are there so many dead trees?” My standard answer has always been a summary of what I’ve learned from talking to Yosemite rangers: The drought has stressed the trees and made them more susceptible to the bark beetle. This morning I read an excellent summary of the problem on the NPS Yosemite site explaining the problem, and adding to what I already knew, and I thought I’d share what I learned.

The problem

As someone who has been visiting Yosemite for (pretty much literally) my entire life, the tree death in Yosemite Valley in the last five years has been staggering. Yosemite Valley, once a carpet of green, is now stained with large patches of rust-brown dead or dying trees. Scenes I’ve photographed for over 40 years are suddenly marred by these trees.

Going through my portfolio of Tunnel View images, I chose two with very similar compositions that illustrate the tree death. The first, my rainbow image from 2009, shows the green valley floor I remember. The second is a winter scene from 2016, and the tree death is obvious. And sadly, in the year-and-a-half since I took the 2016 image, I guess that at least twice as many trees have died.

Double whammy

The drought has clearly taken its toll on Yosemite’s trees, both by killing the thirstiest outright, and by weakening many others until they become easy targets for a very opportunistic bark beetle. But the problem is not just about weak trees—it’s also about healthy beetles, a lot of them. Consider that while the 2016 image was taken in late January, there is absolutely no snow in Yosemite Valley. Of course the drought has something to do with that, but the lack of valley snow in recent years can also be attributed to warming temperatures. As Yosemite’s climate warms, much of the precipitation that once fell as snow now falls as rain.

Snow doesn’t kill the bark beetle (it’s still not cold enough), but an extreme freeze does. But as the number of sub-freezing days in Yosemite decline, the mechanism that kept the bark beetle in check gets out of whack. While Yosemite’s evergreens have no problem handling an extreme freeze, each freeze kills many bark beetles. But fewer freezing days each winter means more bark beetles, and more bark beetles makes even healthy trees more prone to attack.

Triple whammy

And finally, America’s long-time knee-jerk fire suppression policy has taken its toll. By thinning growth, consuming dead wood, and enabling regeneration, fire is a natural part of maintaining forest health. But for over a century, fires in Yosemite (and pretty much every other national park and forest) were doused as soon as they ignited because they were inconvenient, and they (temporarily) scarred the scenery.

Thankfully that misguided policy is largely behind us, but its legacy remains. We’re left with too many trees competing for the available water. Some die of thirst, while many survivors lack the resources to stave off a beetle infestation.

What’s being done

The National Park Service has undertaken the monumental task of removing dead and dying trees. Because it’s impractical to remove all of them, the emphasis is on those trees that pose a hazard to people and property. Also, in developed areas the NPS has started prophylactic application of a (naturally occurring) pheromone that discourages the beetles from attacking susceptible trees.

No one knows for sure, but it’s possible that the tree death will stabilize, or even start to decline over the next few years. While the current mitigation efforts might help stem the tide, the primary hope is that an equilibrium will be reached as the most susceptible trees die and forest health is restored through better management. Fingers crossed.

From the horse’s mouth

Here’s the link to the NPS tree mortality article.

The Trees of Yosemite

Click an image for a closer look and slide show. Refresh the window to reorder the display.

6 Comments on “What’s the deal with Yosemite’s dead trees?

  1. We’d all love to see what it really looks like, rather than the beautiful pics you show
    us – thanks.

  2. Gary, I concur with letting the fires burn as long as numerous houses or people aren’t harmed. Don’t know if the “don’t extinguish” includes fires set by campers letting fires getting out of control or just natural caused fires like from lightning. It’s just like “nature”. Personally, I don’t hunt and would not kill an animal unless it was going to kill me but when animals kill other animals in nature, I consider this a natural occurrence.
    Wonder if they can spray from the air?
    In the photo I have from one of your workshops years ago, there are 4 or 5 dead trees in my Tunnel View shots and your eyes are drawn to them.

  3. Thanks, Gary, for the informative post. It is a shame to see what is happening. This past February I could really see the increased in dead/dying trees. Sad! I agree with letting natural fires burn (within reason, of course).

    • You’re welcome, Gail. They now let natural fires burn unless they pose a risk to life or property. This creates something of a Catch-22 because longer an area goes without a fire, the more debris (fuel) accumulates, which only increases the likelihood of an uncontrollable fire. Just driving around Yosemite, even with the debris management the NPS tries to do there, the amount of dead wood on the valley floor is alarming. If a wildfire ever did start in Yosemite Valley, it could turn into an uncontrollable conflagration in a heartbeat. They do perform managed burns in the valley, but probably not enough to eliminate the risk.

  4. It’s sad to see such a beautiful landscape die. But from other areas around the world we can see that nature will find it’s way to handle changes in the environment. Life’s about changes everytime, so it is for nature too. Let’s hope mankind will eventually stop harming the environment on earth and that places already harmed will recover soon. It’s very important that photographers like you document and report about these problems! Kerp up that work!

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