by Emily Howe, aquatic ecologist
I am on the side of the highway in the driving rain, flashers blinking and my collar tugged up to my ears. Trucks full of wooden apple crates roar past in a spray of tire wash. My stash of 10-foot PVC pipes has shifted, and I need to cinch the straps before the whole pile sprawls across the road.
Wrestling the load back into place, I muse that PVC pipes must be the backbone of field science. But ironically, these plastic tubes are essentially giant straws. Cities are banning straws, one after another, to protect aquatic and marine ecosystems. Here I am bringing PVC to a conservation research site.
But this isn’t a story about plastic in the water. This is about water itself.
You know what else sucks water like a straw? Trees. They are natural straws that pull water from the ground, draw life from it and transpire it to the atmosphere. We need our trees. They release water, but they also clean it, store it, and in some cases, even create it! But we also need to protect water in a drier, warming climate. We may need to remove some of these natural straws to do that. So crucially, we need to know: How many trees, and which ones?
Human legacies are cross-wise with climate
Now planted solidly in the Anthropocene, the Earth overwhelmingly bears the marks of humanity. Some marks are ingenious and beautiful. Some forgotten, long-since folded back into the soils of time. But when the legacies we leave tinker with the natural laws of biophysics, they don’t allow us to forget. What goes around, comes around. For each force, there is an equal and opposite reactive force.
Consider the dry forests of Washington State and the American West. After a century of fire suppression, these once naturally adapted forests are now dangerously overcrowded—with too many trees. This, tragically, fuels more catastrophic wildfires. Add the pressure of a warming climate, and hotter temperatures make for thirstier trees, sucking the soils and streams dry.
Can forest thinning also secure water for Washington?
Our prescription to thin overstocked forests and remove fuel for wildfire may present a winning solution for these two pressing climate issues. But also maybe not.
In California’s American River Basin, forest-thinning, wildfire and prescribed burns removed an awful lot of straws and saved 17 billion gallons of water. California’s governor noticed, signing a 2017 bill facilitating watershed thinning to improve water security as well as fire-resilience.
But don’t get too excited to march this technique up the coast just yet.
Remember Washington’s snowpack. It’s a crucial resource for water security in the forests and valleys of the Cascades. But trees’ water consumption is only one piece of the hydrologic puzzle. Tree canopy makes a difference—as an umbrella it can intercept snow and prevent robust snowpack on the forest floor. On the other hand, this umbrella can provide critical shading and wind protection, preventing an early snowmelt. There’s also radiant heat held within the tree bole itself . . . and the list goes on. It’s tricky to determine whether trees are good or bad for snowpack because it so heavily depends on where you are.
We’ve got the gear, now we need the data
We’re piecing the puzzle together for Washington. This past fall, we packed that PVC load, along with ladders, cameras, straps, t-posts, sledge hammers and temperature sensors, and headed east of the Cascade crest. There you find me, wrestling with plastic pipes.
Racing against impending flurries, we set up a network of monitoring sites to determine whether forest gaps or forest canopies result in a deeper, longer-lasting snowpack. Our sites represent the headwaters of Washington’s most vulnerable watersheds, where rivers depend on snowpack for more than 70% of their flow.
We installed time-lapse cameras and temperature sensors alongside SNOTEL stations to pair our observations with meteorological data. SNOTEL sites provide snow depth calibration points, as well as measurements on wind, temperature, precipitation, irradiance (sunniness), snow density and depth. Time-lapse cameras mounted high in the trees will track snow depth by taking snapshots of measurement poles fashioned from long lengths of PVC.
We’ll relate snowpack data to tree canopy using hemispherical camera shots. Temperature sensors tucked in the duff of the forest floor will track snow melt-out dates: once the snow melts, the ground loses its insulating blanket and temperatures swing wildly.
While I wait to see how this year’s snowpack bears out, I’ll be loading up an avalanche transceiver, a pack full of batteries, and a pair of skis to check on my cameras. Record-breaking snow event or not, we’ve got to get those data.