Fossil Creek suffered only moderate damage from the 42,000-acre Backbone Fire, but silt washing into the creek could affect populations of endangered native fish for years to come.
However, the trails and roads by which some 90,000 people a year gain access to the creek got hammered, according to an initial assessment of the damage to the Fossil Creek Wilderness Area.
Overall, the Backbone Fire that in June forced the evacuation of Pine and Strawberry didn’t burn so fiercely that it damaged the soil, according to Janie Agyagos, a wildlife biologist with the Coconino National Forest.
Within the 3,000 acres in the Fossil Wild and Scenic River Corridor, 10% didn’t burn, 54% had low-severity burns and 34% had moderate severity burns. Only 2% suffered the kind of high-severity burns that can cause dramatically increased erosion. Plants have a hard time returning at all in such conditions.
The area right along the creek fared even better. About 96% of those 651 acres suffered moderate to low severity burns. Only 3% suffered high severity burns. Some trees burned right down to the water’s edge.
However, riparian areas have a tremendous capacity to recover from most burns.
“Most trees will recover, but those that die or were consumed will be quickly replaced by new riparian tree species,” said Agyagos. “Riparian vegetation is very quick to recover. We have witnessed trees that appeared to have been totally burned sprout at the base — and we expect good recruitment from seed.”
The Waterfall Trail and the wildly popular waterfall largely escaped the flames, said Alicia Keller, a photographer with Rim Country Search and Rescue who documented the impact of the fire. However, the fire did burn through the bottom of the canyon near the spring source — exposing the springs which had been buried under berry bushes.
So everything’s great, right?
Well, not quite.
The fire had two major impacts, which will have lingering effects — and will likely keep the stream closed to the public on into the spring.
The fire burned over the Bob Bear Trail, which leads from Strawberry down to the spring source at the head of the canyon. The subsequent monsoon rains did a lot of damage to the trail, which will likely remain closed until the Forest Service finds the money to rebuild sections of the trail.
Moreover, the monsoon rains caused heavy runoff and erosion on the seared slopes above the stream. The sediment clogged culverts under roads along the creek, as well as the normally closed FR 708, which leads down from Strawberry to the canyon bottom. FR 502 leading west to Childs also suffered heavy damage. Debris clogs culverts, which forces floodwater up and across the road. Clearing out the culverts and getting the roads back in shape will take time and money.
The condition of the roads and trails will likely keep the public out much longer than the damage to the riparian vegetation along the creek.
The heavy damage to FR 708 and the Bob Bear Trail will also once again complicate the task of Tonto Rim Search and Rescue, which has performed hundreds of rescues in Fossil Creek. The Pine Fire Department and Tonto Rim Search and Rescue have spent years lobbying the Forest Service to improve access along both routes — as well as now-damaged roads in the canyon bottom.
The sediment that washed out road sections also poses a significant challenge for the host of endangered native fish and other rare and endangered plants, insects, mammals and birds that rely on the creek.
Coconino National Forest fish biologist Matt Oneill said sediment has nearly filled in major pools and piled up along the banks of the creek. The once crystal-clear water is turbid and muddy, which can kill fish.
Most of the heavy influx of sediment has affected the stretch of the stream below where FR 708 reaches the canyon bottom — which extends all the way to the Verde River.
“As predicted, sediment input from Boulder (below FR 708) has been significant and has partially filled several pools, including the deep pool at Sally May recreation site,” said Oneill. “Sediment has also been deposited on the stream banks and continues to make the water turbid even though we saw little rain there for two weeks. This embeddedness (sediment covering sand, gravels, pebbles, cobbles) has likely affected the aquatic invertebrate community and may not recover until flows can wash away the fine substrate.”
The springs that feed Fossil Creek are loaded with dissolved limestone. This travertine precipitates out as the water flows downstream, coating the bottom with a layer of dissolved limestone. This usually leaves the water tinged blue green and crystal clear. That’s one reason biologists think crayfish haven’t heavily colonized the stream since the Forest Service returned the spring water to the creek bed in 2005. In that time, Fossil Creek has become a major refuge for rare and endangered native fish. That includes the razorback sucker, loach minnow, spikedace, Gila topminnow, headwater chub, roundtail chub, longfin dace, desert sucker and Sonora sucker. The creek also harbors four rare and endangered macro-invertebrates, including a mayfly species and the fossil springsnail.
Other rare and endangered species include the Merriam’s shrew, western red bat, spotted bat, Allen’s lappet-browed bat, pale Townsend’s big-eared bat, greater western mastiff bat, plains harvest mouse, bald eagle, peregrine falcon, black hawk, northern goshawk, Abert’s towhee, narrow-headed gartersnake, lowland leopard frog, northern leopard frog, Arizona toad, and reticulated Gila monster. The sensitive species list for the creek includes about 50 rare bird species and three endangered butterflies.
All of those species will have to cope with the impact of the silt flowing into the creek from the burned slopes.
Oneill said it will likely take two to five years for flood flows to move the silt filling pools and piled up on stream banks down the creek and into the Verde River.
“Sediment input could continue to fill the pools even if they get cleaned out” by floods. “Sedimentation will also likely continue to reduce aquatic invertebrate abundance and diversity during this time.”
But in the long run, the stream should recover.
“We expect the creek to stabilize and have an aquatic community very similar to pre-fire. It may take several very high flow events to scour out pools to their pre-fire depths, which may take many years, or just one,” concluded Oneill.
He said it’s still unclear how many fish in the lower reaches of the creek got smothered by the silt washing off the slopes during the monsoon — although most of the native fish are adapted to floods and warm, silty water. Oneill said even if many fish in the lower half of the creek got washed away or smothered, fish in the relatively untouched upper section will likely repopulate the creek all the way down to the Verde River.