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Post-fire Vegetation Monitoring on the San Rafael State Natural Area


Background:San Rafael
The San Rafael State Natural Area (SRSNA), owned and managed by Arizona State Parks, is approximately 3,500 acres in size and consists of short grass prairie with oak woodlands at higher elevations. The headwaters of the Santa Cruz River, dominated by mature Fremont cottonwood (Populus fremontii) and Goodding willow (Salix gooddingii), bisects the area from north to south.  In May 2007, a human-caused fireoccurred within the riparian corridor and adjacent uplands.  Arizona StateParks determined that approximately 600 acres burned on the SRSNA during this event.  In 2008, a complete inventory of trees (live and dead) was conducted along the riparian corridor to evaluate post-fire tree survivorship.

The SRSNA is located within the San Rafael Valley, between the Patagonia Mountains and the Huachuca Mountains, approximately 90 miles southeast of Tucson, Arizona. 

The SRSNA portion of the Santa Cruz River riparian corridor is comprised of six sub-watersheds and the main channel of the Santa Cruz River.  In July and August 2008, we located all live and dead (snag) trees within each area, and measured species composition and tree diameter.  For each snag, fire-related death was determined based on evidence observed in the field (e.g., sloughing bark, trunk girdling) and regeneration of live stems (e.g., coppice sprouting, root sprouting) was noted if present.

The number of large trees (DBH > 60cm) located along the main channel and sub-watersheds totaled 480 and 733, respectively.  Of these totals, a higher percentage of snags (83.6%) were observed along the drier sub-watersheds compared to the wetter, main channel (34.0%) suggesting increased fire severity within these areas.  Regeneration of live stems on snags was observed at a higher percentage of trees along the main channel than within the sub-watersheds.  Even though the majority of post-fire snags with regeneration were top-killed by the fire, these trees were not included in calculations of overall loss since they were not complete mortalities.  Overall loss of large trees along the main channel was calculated at 9.2% while almost 47% of the large trees were lost along the sub-watersheds.  Planting native vegetation such as cottonwoods and willows is being considered to mitigate the loss of trees and supplement natural regeneration. 

Fire frequency and severity have increased in southwestern riparian areas in recent years, but the role of fire in these systems is not well understood.  Data on the response of native riparian plants to fire in the southwest are also limited. The 2007 fire on the SRSNA presented an opportunity to evaluate the short-term response of riparian vegetation to fire within two distinct areas: the wetter, main channel of the Santa Cruz River and the drier, more terrestrial sub-watersheds.  Collected data provided important information on post-fire survival of native woody plants, such as Fremont cottonwood and Goodding willow, in southeastern Arizona. 

For more information contact:
Angela Stingelin, Arizona Game and Fish Department
5000 W. Carefree Highway Phoenix, AZ 85086-5000.
Phone: (520) 742-1911            Email:

Michael Ingraldi, Ph.D., Arizona Game and Fish Department
5000 W. Carefree Highway Phoenix, AZ 85086-5000.
Phone: (928) 532-5625            E-mail:

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