Letter From Jim Brobeck to Chico Park Director Regarding Controlled Burns Near Alligator Hole
November 13, 2000
I would like to have this matter put on the agenda for the November 27 Park commission meeting.
Chico has conducted prescribed burning on several plots of upper Bidwell Park in an experiment to use fire as a tool in the control of yellow star thistle. I have taken particular interest in the plot that is across the road from the Alligator Hole parking area. This acreage has been burned three years in a row. The next crop of star thistle is beginning to sprout. The blue oak trees on the test plot are being damaged by the experiment. A survey conducted by local citizens found that of 53 mature oak trees 36 have had damage to the bark at ground level and/or to the foliar crown and 8 trees have died due to the effects of fire. The stress associated with the prescribed bums has caused epicormatic sprouting in many trees.
Blue oaks are adapted to occasional fire as evidenced by the root sprouting of approximately 68 of 100 saplings. But the annual use of fire kills the young sprouts and tests their ability to recover. Fire return regimes of 5-15 years are considered normal by some researchers but Robert Cermak and John Ost think that 50-80 years is more likely to be the normal cycle. Mature blue oak trees (over 6″ diameter) do not sprout from the roots when killed. Wes Dempsey estimates the age of the mature trees killed and damaged to be 100-250 years old.
Trees with rot pockets and channels including snags are particularly useful to wildlife. They are used as shelter. In fact Wes found a young rattlesnake coiled in one ground level pocket during our November 3 field trip. These trees are particularly sensitive to fire because the blaze can enter the tree and cook it from the inside out. There were two snags reduced to ash during the prescribed bums.
If the experimental use of frequent fire to control yellow star thistle is continued the oak trees need to have pre-ignition treatment. At the very least the fuel from around the base of the tree must be removed and a protective barrier of foam or gel must be applied to prevent fire from destroying the bark and entering cavities. The extensive foliar damage and epicormatic sprouting indicates that the fire must be kept even further away from the blue oak trees to prevent the heat and flames from scorching the leaves.
The tree damage done by these experiments is unwarranted especially if fire is ineffective in controlling yellow star thistle infestation.
Survey of Plant Survival Alligator Hole Parking Area Burn
Mature Blue Oaks
Damaged 1999 and 2000: 36
Damaged 1999, not damaged in 2000: 7
Undamaged in 1999 and 2000: 2
Killed in 1999 7
Killed in 2000 1
Snags reduced to ash in 1999 2
Sapling Blue Oaks all Crown killed in 1999 and 2000
Resprouted in 2000 68
Have not resprouted in 2000 33
Crown killed and resprouted in 1999 and 2000 46
Crown killed in 1999, not damaged in 2000 12
Crown killed in 1999 and 2000, not resprouted 11
Crown killed in 1999, did not resprout 3
Notes and Comments
Bunch grass clumps reduced in size in 1999 and further reduced in size in 2000.
Non-native annuals are invading the former domain of the bunch grasses.
Many Blue Oaks have less foliage damage in 2000 than in the 1999 burn, but still incurred additional root crown damage in 2000.
Jim Brobeck, Chico