Fire is a common agent of disturbance in grassland ecosystems. The removal of cattle from the Sevilleta National Wildlife Refuge (SNWR) after 1973 resulted in an increased number of lightning-initiated wildfires which left a mosaic of burned patches across the landscape. Prior to 2002, lightning-initiated wildfires were actively suppressed, but have since been allowed to burn. The effects of fire on post-grazing vegetation have been addressed in several studies. Fire effects have also been incorporated into several other studies following unexpected wildfires. Fire effect studies include:
1) Antelope Exclosure Burn Experiment: 1993
This study was based on a random block design incorporating 16 300 m x 300 m plots on the southern end of Mckenzie Flats where a mixed blue and black grama matrix was being encroached upon by creosote bush. Eight of the 16 plots (72 ha) were burned in 1993. Half of the burned and unburned plots were fenced to examine how excluding indigenous pronghorn antelope impacted vegetation. Sampling consisted of quantifying grass cover by species in 3 m x 4 m quadrats within the larger plots via “boom” photography.” The dimensions of shrubs before and after the fire were also measured, as were effects on populations of small rodent.
2) Antelope Exclosure Burn Experiment: 2003
A large prescribed fire was carried out in the early summer of 2003. This fire consumed half of the burned plots included in the 1993 Antelope Exclosure Burn Experiment, as well as nearly 5000 additional hectares of McKenzie Flats. An array of vegetation measurements in burned and unburned areas have tracked the recovery of vegetation since 2003. These measurements include:
Grass Species Composition – Four replicate small quadrats (30 cm x 30 cm) are sampled at six randomly-selected 3m x 4 m plots across each of the 16 plots to quantify the composition of grasses post-fire.
Species Composition of Forbs and Grasses – Spring and fall measurements of vegetation cover are performed by sampling all species within ¼ m2 quadrats at 96 points within each of the 16 plots.
Shrub Recovery – The survival and recovery of shrubs and subshrubs, including creosote, yucca, and Mormon tea, were measured before and immediately after the fire and at irregular intervals since.
Fuel Load Recovery – The vegetation adjacent to each corner of the 3 m x 4 m plots located within the larger plots is collected to obtain a measure of standing biomass at the end of each year.
Net Primary Productivity – Paired burned and unburned plots were established in 2004 within the major vegetation types to quantify above-ground primary production. Vegetation associations included: 1) black grama grassland; 2) black and blue grama grassland, and; 3) black grama and creosote savanna. Plots are not limited to the area of the 1993 burn.
3) Burn Transects Across a Burn Boundary
A lightning strike in June 1995 left a small burn scar on McKenzie Flats. Four 100 m transects were established across the boundary of the burn with half of each transect in a burned area and half in an unburned area. Transects were measured annually and sometimes more frequently. In 2001, a larger lightning-initiated fire burned the southern boundary of the initially burned area. The transects which were then partially freshly burned and partially burned in 1995 continued to be sampled. In 2003, it was decided to re-burn the 1995 burn portion of the transects. Thus, the four transects were each burned twice; two in 1995 and 2001 and two in 1995 and 2003.
5) Seasonal Fire Experiment
Native vegetation is the key resource upon which rangelands are built, and restoring rangeland ecosystems are one of the most critical challenges facing rangeland managers today. This experimental fire research project, in collaboration with the USFWS and the Sevilleta LTER, is intended to provide FWS and other land managers of southwestern grasslands and rangelands with information about vegetation recovery following fire under different seasonal conditions and burning treatments. This experimental research will enable the FWS to more effectively set project objectives for prescribed burning on the Sevilleta NWR to benefit not only wildlife habitat, but to better align the timing and intensity of fire to benefit the reestablishment of the dominant native grama grasses Bouteloua eriopoda and B. gracilis. Since its creation in 1973, management has been devoted to restoring the Sevilleta NWR to the natural conditions that might have been seen around the turn of the century. The Sevilleta NWR is an ideal place for research because climatic conditions, plant species composition and net primary production following wildfire have been well documented by the Sevilleta LTER. Additional experimental research is needed, however, to better inform managers about the timing and use of fire as an ecosystem restoration and management tool. Data collection and analysis will be continued by the Sevilleta LTER beyond the requested funding period.
4) 2009 Wildfire
A lightning-initiated wildfire in August 2009 consumed over 3000 ha in an area where an array of experiments had been proceeding for some time. Portions of these experiments are now describing experimental effects within a burned matrix.