A rumor came my way last week that is so off base I am writing about it today.
On Highway 101 in south Pacific County, there is a straight stretch of road from Bear River to Greenhead Slough. Last year, a bridge replaced a very undersized culvert near the north end of the straights. That summer, trees began dying along the highway, upriver from the new bridge.
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| June 2016: Sitka spruce and Pacific crabapple trees are dead and dying along the road south of the new bridge; which is immediately to the left of this image. The road in the foreground is Highway 101; Bear River is to the right, looking south east along the highway. |
The rumor is that this area was sprayed with herbicide as part of industrial forest management.
Marshes are not industrial forests; this low forest and marsh area is part of the Willapa National Wildlife Refuge. Corporate timber growers do not waste money spraying non-logging areas, especially on land they do not own.
So if this area wasn't sprayed, what happened?
When the drainage was opened with a bridge in 2015, the upper reaches of the marsh east of the highway returned to the old hydrology pattern––fully tidal––which means that tide waters are higher at high tide than they have been for six or seven decades. Water levels are also lower at low tide.
Fish, including salmon, can now easily enter the ditch along the highway, and from there, five or six streams that drain from the hills to the east. Floods no longer surge up to the road edge on the east side, held back by a small culvert and tide gate. Given that we have experienced more flash floods in recent years than in decades before, this is good.
Trees, especially conifers that grew behind the tide gate, were abruptly exposed to saltwater on very high tides, and their roots began to die as soon as this salt exposure started. Sitka spruce, Picea sitchensis, is the dominant large conifer tree along the edge of Willapa Bay. A small hardwood tree, Pacific crabapple, Malus fusca, is also common in the marsh [the small gray bubbles in the background of the photo are crabapples]. Both trees grow on slightly higher ground than the main marsh level.
Summer 2016 is the second growing season with full tidal cycling, and the trees are now dead or dying along almost a mile of road. A few spruces are still green; these are trees that are slightly higher in growing position than those that are dead.
Both species tolerate some salt exposure. The new hydrology brought too much salt to their roots, however. Six months of dry weather last summer probably accelerated the impact. The result was that several dozen conifers and even more crabapples abruptly died.
If you look east across the marsh into the hills, you will see that trees on the slopes and at the base or toe of slope above the marsh are alive, still green and in active growth. Only the trees that were too low have died.
There is another place to see the same sort of response to a change in hydrology, also on Highway 101 in south Pacific County, on Chinook River. Here the tide gate is closed only on extreme high tides, and the rest of the time, the gates are open so that fish can move more easily in and out of the river.
Just east of the highway, there was a stand of alder; now it's a stand of snags with salt marsh sedges and other species covering the ground. This transition took just a few years with new gate management methods. The spruces behind the alders were high enough in position to keep living.
Better management of water through changes in tide gates, or replacing gates with bridges means that fish can access their natal streams more easily. It also means that during periods of high rainfall more water drains off more quickly. These are good outcomes. But for trees that began growing in locations that were not quite high enough, it means that they can no longer live in those locations, and it's that abrupt change from alive to dead that catches our eyes as we drive Highway 101.
