“Do you know what’s going on with these trees?” wondered my coworker as we made our way up the trail.
I’d been looking around. Seemed like there were a lot more dead ones than a couple years ago. This observation follows a pattern I’ve been seeing all spring and into summer—lots of dead and dying trees.
There’s always mortality in a forest, always some trees dying and making space for the next generation coming up underneath. A variety of agents kill trees, from events like windstorms and fires to biological causes like insects and fungal disease. The classic attitude to insects and disease sees them as bad, putting an anthropocentric spin on anything that causes loss of value to the human economy. Rotten trees = waste of extractable resource = loss of profit. However, after a few years of walking in the woods and looking around, I came to the conclusion that bugs and mushrooms are part of the forest ecosystem, having evolved with the conifers that host them. Some insects and fungi are specific to only one species of tree. Others are more tolerant of other species, especially when conditions are right.
In the early 2000s, the forests on the east slopes of the Cascades experienced a spruce budworm outbreak that lasted nearly the whole decade. The insects are small gray very plain moths which lays their eggs in the tips of conifer branches in the late summer. The eggs overwinter and hatch when the buds burst in spring to produce succulent needles which the little green caterpillars proceed to devour. The moths are endemic, meaning that they live in the forest all the time. What caused the outbreak, or epidemic, was the abundance of food. One hundred years of fire exclusion allowed shade-tolerant grand firs to proliferate under an overstory of ponderosa pines and Douglas-firs that are adapted to frequent low intensity ground fire. It’s almost as if Nature said “Well, if you won’t let me use fire, I’ll find another way to wipe out some of these extra trees that don’t belong here.” In those years, a hiker could almost hear the millions of tiny caterpillar jaws munching on fir needles. And certainly the millions of tiny pellets of caterpillar feces falling were audible. It sounded like very light rain on a nylon tent at night.
The defoliation swept through valleys and up ridges. Trees turned red as they died from the top down. When the red needles fell, all that remained were the ghostly gray skeletons. As the budworm population exploded, there were so many caterpillars that they began to look beyond their preferred food to any food. The ponderosa pines and western larches escaped, but every other conifer species was affected. I saw defoliated hemlocks and white pines. Many many of the understory trees were killed, and many overstory trees were weakened by years of successive defoliation.
When the budworms ate themselves out of house and home, the population crashed. It looked as if the forest might return to some kind of equilibrium.
But then the Douglas-fir bark beetles moved in. Bark beetles are also endemic, always present at a low level. They have the ability to detect distressed trees. Plants communicate with each other through the release of hormones. A tree can signal to its neighbors that it’s having trouble, and those neighbors can share nutrients through root networks. Insects also communicate with chemical messages, and bark beetles intercept the signals sent by trees. The adults tunnel through the bark and lay eggs in the cambium, that thin layer of living tissue which transports water and nutrients from the foliage to the roots. When the cambium is damaged, the tree is weakened and may die.
Now, add prolonged drought to the equation. Trees that are already stressed have one more difficulty to contend with. Their biological imperative is to reproduce. Desperate trees put all their energy into producing one more crop of seeds before they die—if they can’t survive, perhaps their progeny will. It may look as if a healthy tree is covered with cones, but it’s called a stress crop for a reason. It’s the last ditch effort of an organism that has been pushed to the edge.
So when my coworker asked if I knew what was going on with those trees, I replied “Stress,” and gave a few details about budworms, bark beetles, drought. Then added “Climate change.”
More dead trees means more fuel for the inevitable wildfires that come every summer. Climate change means that they burn hotter and longer, grow bigger and potentially more devastating.
One climate model predicts that places in my familiar landscape will be unable to support trees in fifty years. This boggled my mind, but not for very long.
There’s an old saying that the road to Hell is paved with good intentions. That seems to apply here. Humans thought they were doing a good thing by suppressing wildfires to save the forests for all the reasons we want forests. So that we have lumber to build homes for people. So that the animals have homes. So that we have green forests to play in, and green forests for watersheds. But it is now obvious that there were unintended consequences. Much effort is being made toward “restoration” of our forests, to try to correct the ignorance and mistakes of the past. I don’t have much to say about this except to wonder if we are still trying to do good things that will themselves have unintended consequences. Thomas Edison famously said that the first step in intelligent tinkering is to save all the parts. We didn’t do that, therefore any tinkering at this point is probably not intelligent. Especially if it comes from the same mindset that created the original imbalance.
There are many possible responses to stress. Left untreated, stress is a killer. Some of us deny that there’s a problem, some of us self-medicate with the vice of choice, some of us give in to despair, some of us look for rescue from the next technology or charismatic leader. Some of us put all of our energy into one last flush of cones. Some of us ask for help from our neighbors, and dig deep into our roots for whatever resilience we can muster.
There’s a long hot road ahead. There will be less shade cast by trees. Consider this, and pay attention to good intentions.