Healthy Forests, Healthy Streams

The key to a healthy desert stream is its watershed, or all the land above that drains water towards the stream itself. The watersheds for streams around Tucson reach into the upper-mountain oak woodlands and conifer and aspen forests. Before 1900, these plant communities typically burned every few years in relatively small ground fires. But improvements in firefighting had an unhealthy side effect of allowing the buildup of dead wood and small trees, which created conditions for large fires such as the 2020 Bighorn Fire in the Santa Catalina Mountains.

 

Left image
Tinaja in Saguaro National Park before the 1999 Box Canyon Fire, filled with water.
Credit: NPS Photo

Right image
The same tinaja after the 1999 Box Canyon Fire, filled with sediment.
Credit: NPS Photo

 

Unfortunately, huge wildfires can damage streams by killing trees, disturbing soils, and causing rain to runoff rapidly in flash floods and mudslides instead of soaking into the ground to recharge the aquifer. When it rains after a large fire, there are no small plants like shrubs and grasses to catch and hold the water in the soil. Instead, water runs off the surface of the ground and carries the top layer of soil with it, gathering more and more sediment as it flows towards the nearest stream. Massive floods and debris flows after the Helen's 2 and Box Canyon Fires in Saguaro National Park led to nearly all of the tinajas in the watersheds becoming buried in sediment, killing native frogs and other aquatic animals by pushing them out of their habitat. Research at the park reveals that it can take decades for the sediment to clear out, by which time it is far too late for the species to reestablish their population.

 

Rincon Creek flows with water shed off the higher elevations of the Rincon Mountains, including Rincon Peak seen in the distance

NPS Photo

Ultimately, healthy streams are the result of healthy forests that are allowed to burn naturally. Fire managers also use prescribed burns, forest thinning, and water retention structures to reduce fire intensity and erosion and nurse damaged ecosystems back to health.

 

Learn more about fire effects: How do invasive grasses affect desert fire?

 

Wildland firefighter uses a drip torch to ignite low-intensity burning during management of the 2014 Deerhead Fire in the Rincon Mountains

NPS Photo