Battle Flat Watershed Pilot Project

Results, Implications, and Current Status

Results

Although extensive instrumentation, inventories, and baseline research studies were performed on the Battle Flat Demonstration Area, treatment of the entire watershed was never accomplished because of the political and legal constraints surrounding the widespread use of soil-applied herbicides for treating watersheds. However, one small area on the Battle Flat watershed, was prescribe burned in 1985. Measurements associated with this prescribed fire, along with other inventories and studies, added to our basic understanding of chaparral shrublands.

Battle Flat

Sediment accumulations in the two stock tanks prior to treatment with prescribed fire showed that sediment production from chaparral is primarily the result of winter periods of heavy precipitation and runoff and generally not from summer rainstorms (Hook and Hibbert 1979). The sediments came mostly from erosion of channel alluvium in upstream tributaries where the sediments accumulated from downslope creep, dry ravel, and overland flow produced during the typical, smaller, convective rainstorm events. The study further concluded that:

• The long-term sediment rate from the unburned watersheds was about 0.6 lb/ac annually, but increased to almost 2.7 lb/ac (about 4 times) during winters of heavy precipitation.
• After the prescribed burn, sediment yields increased to over 7 lb/ac (about 12 times) annually for the three years following the fire (Overby and Baker 1995).
  Prescribed burn
• The increased erosion resulting from the prescribed fire removed substantial amounts of nitrogen, phosphorus, and cations from the burned watershed (Overby and Baker 1995). Both concentrations and amounts of these nutrients increased in the sediment material that was eroded from the burned areas.

A separate study on the small watersheds within the Battle Flat Watershed showed that interactions between species composition and aspect have an effect on nutrient responses to prescribed fire. Higher preburn nutrient concentrations were found under shrub live oak compared to those under mountainmahogany (Klemmedson and Wienhold 1991a). Phosphorus was also a limiting nutrient before burning, particularly on south aspects (Klemmedson and Wienhold 1991b).

The results after the prescribed burn indicate:

• Ammonia and phosphorus were translocated downward in the soil as a result of fire (Overby and Perry 1996).
• Residual ash and underlying soil contained increased concentrations of available nitrogen and phosphorus. This temporarily increased soil fertility on the burned sites.

Fire history for the Battle Flat watershed was established back into the mid 1800s (Dieterich and Hibbert 1990). Reconstruction of the history showed that:

• Fires burned at an average 2-year interval within the 200 ac ponderosa pine stand and surrounding chaparral, before intensive mining activities began in the 1860s.
• Ponderosa pine and associated oak and juniper trees were heavily cut during the expansion of local mining activity from 1863 to 1885, after which fire protection, low fuel loading, and grazing essentially eliminated large fires for many years. This resulted in the present day chaparral stands being overmature, lacking a natural mosaic appearance and containing heavy accumulations of dead material.
• Large wildfires have swept through continuous stands of dense chaparral, since the 1900s as a result of the large fuel accumulation.

Implications

Research and management efforts in Yavapai County consisted primarily of testing previous research findings on experimental watersheds and on an operational scale. Studies at Whitespar and Mingus experimental watersheds extended the information gained from the Three-Bar watersheds and Natural Drainages watersheds in the Salt River Valley. It was concluded from the investigative studies that:

• The mosaic pattern (where about 50% of the brush was treated with soil-applied herbicides and fire) was beneficial for increasing water yield, maintaining water quality, improving wildlife habitat, and reducing fire hazard.
• The availability of soil nitrogen and phosphorus increased as a result of the burning and these fire-related responses were affected by plant species and aspect. The increased nutrient availability disappeared after 2 yr.
• Sediment production and nutrient loss increased even after low-intensity prescribed burns.
• Long-term productivity and sustainability of chaparral ecosystems were enhanced by prescribed fire.

Current Status

Streamflow and precipitation measurements were continued at Battle Flat through 1989, then all data collection was terminated.