A fellow wildlife biologist once told me that if you don’t write it down, it’s like it never happened. Throughout my career I have filled dozens of notebooks detailing my observations of all things wild. I’ve transcribed those notes onto data sheets, which I then entered into databases. Those databases were ultimately backed up on hard drives, servers, or the cloud. I left behind what I hope will be a permanent record of my observations. But what do you do if you want to know what happened before humans were writing things down, or even before humans were at all?
I was pondering this question while sifting through a pile of bark beetle data for Cedar Breaks National Monument. Cedar Breaks sits along the edge of the Markagunt Plateau in southwestern Utah. Most of the monument lies within the highly erodible, steep and colorful sandstone cliffs known as the “breaks,” but above the breaks are dense forests of Englemann spruce and subalpine fir. I’m trying to figure out how much of the monument’s forested landscape has been affected by bark beetles and what that says about forest health there.
Bark beetles are a group of insect that infect coniferous forests across North America. There are a hundred or more species, but less than a dozen kill their hosts and each specializes on one or a few trees. The fir engraver specializes on white fir, California red fir, and grand fir. The mountain pine beetle infects ponderosa pine, whitebark pine, bristlecone pine, and lodgepole pine. The spruce beetle infects Engelmann spruce, white spruce, Sitka spruce, and Lutz spruce. You get the idea.
These beetles kill their hosts by laying their eggs in a tree’s soft living tissue (phloem), which is just beneath the bark. When the eggs hatch into larvae they chew tunnels or galleries through the tree’s arteries, interrupting the flow of nutrients and water and in the process introduce a fungus that further weakens the tree. Because bark beetles infect mostly weak and mature trees, seedlings and saplings left behind are released from competition and shoot into the canopy.
Bark beetles are agents of change. They shape forests by causing death and then allowing for re-birth. Bark beetles have been in this dance with western coniferous forests for thousands of years, well before anyone was writing it down and perhaps even before humans were at all.
But throughout the western U.S. billions of trees across millions of acres have been killed by bark beetles over the last few decades. The severity and scale of today’s insect outbreak is widely believed to be unprecedented. Words like “devastating” and “catastrophic” are often used to describe what is happening across the west. This isn’t wrong, but it’s not exactly right either.
The trouble is that bark beetles are native insects. They have the right to do what is necessary for survival. Who are we to say when their actions have caused too much damage? Is that within our purview?
Since the 1990s, the U.S. Forest Service has been mapping beetle outbreaks across the west. Lucky for me the Forest Service makes all their data publicly available so I download a portion of it for an area around Cedar Breaks. Because I’m a visual person and because I’m a sucker for maps, that’s where I started, and I don’t like what I see.
A huge swath of overlapping bubbles appears on my screen covering nearly the entire area of spruce-fir forests above the breaks. Each bubble indicates an area that has been mapped as dying or dead. These are places where needles turned orange and then fell to the ground leaving behind gray-barked skeletons – a forest of ghosts.
The death of a forest strikes me as wrong somehow. Maybe because I won’t live long enough to see it regenerate. This forest, as is true of most forests, lives on another time scale separated from mine by hundreds of years. I need to get on forest time to understand what this map means.
I close the map and begin searching the web for studies that might help. I want to know what the natural range of variation is for beetle activity in a forest like this, which is a fancy, science-y way of asking what is normal.
I find a few studies that suggest sustained bark beetle outbreaks have occurred episodically in the past, but these studies only go back a few decades, perhaps a century — the lifespan of a very lucky human but not of a forest. I want to go back further to at least a few hundred years (a few thousand would be better) because the current bark beetle outbreak might be within our purview. We might be partially responsible, and I want to eliminate the human animal as a suspect.
It’s no secret that humans have and continue to change the climate, and we’ve been changing things for a long time. Warmer temperatures have sped up the life cycles of bark beetles and have increased their overwinter survival, which means more beetles to infect more trees. A drier climate also means that trees are more stressed than usual, thereby increasing their susceptibility to attack. Under a warmer climate beetles have even spread north into forests that have no record of past bark beetle outbreaks. Like a divining rod revealing hidden sources of water, the finger of blame is pointing in our direction.
Still, I need to know what is normal in order to determine if the current outbreak is “devastating” and “catastrophic,” but I’m not having much luck with my search until I stumble on a study going back 400 years – a full three centuries before any of the others. Perhaps this one will provide the answers I’m looking for.
Using a combination of tree-ring growth, evidence of feeding galleries created by larval beetles, and the occurrence of fungus introduced by the beetles, researchers have found that outbreaks of mountain pine beetles occurred at regular intervals over the last 400 years, and that they tend to be synchronous across North America, meaning that large scale outbreaks were not that unusual even before climate change. But the further back in the tree-ring record these researchers went, the fuzzier the story became. Like humans, the earth begins to forget. Records are lost. Trees decompose.
What they did find is that beginning by about 1910 outbreaks across North America became increasingly synchronous suggesting a shift in bark beetle activity that is probably a cascading effect of climate change. But how much have bark beetles been influenced by us? How many trees would have been spared if we had made other choices?
This study, like the others, does not answer these fundamental questions. I am no closer to the truth of knowing what is natural. As a scientist this is frustrating; as a human it is humbling.
I open once again the map of Cedar Breaks National Monument. On my screen are bubbles dating back to 1997, the year after I graduated high school. Such a short time for a forest; such a long time for a human. And I am left to wonder how far back must we go before we are comfortable with our role as human animal – as agents of change ourselves. Is there such a time?