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    Author(s): Zachary Principe
    Date: 2015
    Source: Gen. Tech. Rep. PSW-GTR-251. Berkeley, CA: U.S. Department of Agriculture, Forest Service, Pacific Southwest Research Station: 175-185
    Publication Series: General Technical Report (GTR)
    Station: Pacific Southwest Research Station
    PDF: View PDF  (182.0 KB)

    Description

    Engelmann oaks (Quercus engelmannii) are restricted to extreme southern California and northern Baja, California. Their entire range falls within a landscape increasingly prone to human induced wildfires. The influence of fire on seedlings and saplings has been well studied, but there is less information available on its effects on mature trees. Two monitoring programs tracked Q. engelmannii for 13 years in areas experiencing fires and adjacent unburned areas. At the Santa Rosa Plateau Ecological Reserve, management fires were initiated in 1988. Management units have been subjected to grass-layer fires from one to three times. Damage at the base of the trunk was present in roughly half of the surveyed trees. During the survey period, 4 percent of the trees died in 4 categories; (1) killed directly by fire (46 percent), (2) obtained trunk damage that may have led to mortality 3 to 6 years after fire (15 percent), (3) had no visible fire damage (23 percent), or (4) had fire scars, but died more than 8 years after the most recent fire (15 percent). An Engelmann oak monitoring program was initiated in 2000 on the Santa Ysabel Open Space Preserve (SY). The 2003 Cedar Fire burned portions of SY and the oak monitoring sites. Sites were surveyed after the fire to assess trees for damage and again in 2008 and 2013. On SY, Q. engelmannii grow in three matrix vegetation communities, grassland (with cattle grazing), sage scrub, and chaparral. Fire damage differed among communities. Trees in grasslands received the least amount of damage, those in sage scrub received intermediate damage, and those in chaparral the greatest damage. Survival was inversely related to damage which resulted in large difference in survival among the three communities. In surviving trees, sprouting type appeared dependent on the amount of damage trees received. Basal sprouting was common in highly damaged trees while crown sprouting was most common in trees with low levels of damage. Engelmann oak trees appear resistant to grass-layer fires which generally result in low levels of damage and mortality rates similar to adjacent unburned areas. Trees are sensitive to higher levels of damage associated with greater fuel loads in sage scrub and chaparral. Although, basal sprouting is uncommon in mature trees following damage, trees able to survive high levels of damage can persist as shrubs for at least a decade. As a result, the structure of the vegetation community is simplified with the loss of the tree canopy.

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    Citation

    Principe, Zachary. 2015. Influence of fire on Engelmann oak survival – patterns following prescribed fires and wildfires. In: Standiford, Richard B.; Purcell, Kathryn L., tech. cords. Proceedings of the seventh California oak symposium: managing oak woodlands in a dynamic world. Gen. Tech. Rep. PSW-GTR-251. Berkeley, CA: U.S. Department of Agriculture, Forest Service, Pacific Southwest Research Station: 175-185.

    Keywords

    Engelmann oak, prescribed fire, Quercus engelmannii, wildfire

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