Sam Johnson Pine and Oak Response to Fire in the Sierra Nevada Foothill Savanna May 8 2006 Pine and Oak Response to Fire in the Sierra Nevada Foothill Savanna Sam Johnson Abstract The pine oak savanna of California s Sierra Nevada foothills has been greatly altered by the introduction of cattle grazing exotic annual grasses and the suppression of fire Fire is an important element of the disturbance regime of an ecosystem and is a common management tool for wildlands Therefore it is important to understand the effects of fire on the growth rate of tree species native to this ecosystem I used woody debris line intercept sampling and Brown fuel transects to quantify fuels consumed by a controlled burn treatment at the University of California s Sierra Foothill Research and Extension Center SFREC in the northern Sierra Nevada mountains I used the difference in ground fuels before and after the burn as a proxy for the fire intensity and compared the difference against tree diameter growth rates before and after treatment Quercus douglasii and Pinus sabiniana both showed a significant negative difference in normalized rates of radial growth in the first year following the prescribed burn I did not find a significant correlation between radial growth and fuels consumed on a sub watershed scale I developed a model to explain the relationship between woody debris and Brown fuel transects This pilot study suggests that a more in depth study is needed to understand the relationship between fire and tree growth here Longer term trends can only be determined future measurements of tree growth Further work needs to be conducted on the specific parameters which best suit the implementation of woody debris and or Brown fuel transects in the savanna ecosystem p 1 Sam Johnson Pine and Oak Response to Fire in the Sierra Nevada Foothill Savanna May 8 2006 Introduction California s Sierra Nevada foothills contain extensive blue oak savanna ecosystems which have attracted attention as part of ongoing debates about the ecological role of fire and appropriate use of fire as a management tool However very few studies have been conducted on the blue oak savanna and those studies which have examined these ecosystems have treated them as co existing grassland and a woodland forest ecosystems not as a form in its own right Approaching a savanna as a distinct ecosystem has the potential to more precisely describe and understand the unique dynamics of the system Some past research has been conducted on similar pine wiregrass systems in the southeastern US Mitchell 1999 but conundrums outlined by House et al 2003 limit and restrict the results of savanna study They noticed that in order to better understand savanna dynamics research must acknowledge three conundrums which most studies of savanna systems fail to thoroughly address House et al pose the conundrums as three questions which most studies of savanna systems fail to thoroughly address How is the woody and herbaceous plants ratio controlled How do they interact How does the net primary productivity NPP change with changes in the woody herbaceous plant ratio To address these questions the savanna ecosystem must be viewed as a continuous ecosystem not a mixture of grasslands and woodlands Previous studies on blue oak savanna e g Callaway 1991 Dahlgern 1997 Kay 1987 examined tree growth at the University of California s Sierra Field Research and Extension Center SFREC but none of these studies took a continuous ecosystem approach Ecosystem scientists recognize a model developed by Hans Jenny as one of the seminal works in the field This model consists of five state factors which act upon ecosystem processes and affect what organisms exists for a particular set of state factors as shown in Fig 1 Jenny 1941 originally developed the idea of five independent state factors to explain soil processes but ecologists later used this model to explain ecosystem processes in general Chapin et al 1996 revised Jenny s model to include the concept of four interactive controls which unlike state factors both affect and are affected by ecosystem processes Fig 1 Many ecosystems have evolved with particular disturbance regimes an interactive control of the state factors climate and time of which fire is an essential component Chapin et al 1996 Savanna systems are one such ecosystem John Battles 2005 has proposed that three major changes have taken place in California savanna systems First native grasses have been replaced with non native grasses Second fire has been removed from the ecosystem Third cattle grazing has been p 2 Sam Johnson Pine and Oak Response to Fire in the Sierra Nevada Foothill Savanna May 8 2006 introduced to the ecosystem Interestingly enough these ecosystems seem to be fairly stable Battles 2005 has further suggested that grazing has taken the place of fire to keep r selected species herbaceous plants in check while giving k selected species woody plants a chance to thrive but the effects of fire on growth have not been studied on a blue oak savanna as a continuum of woody and herbaceous plants My study examines how tree diameter growth correlates with fire intensity in a savanna dominated by blue oak Quercus douglasii and ghost pine Pinus sabiniana trees on plot and watershed scales It also quantifies fire intensity by the difference in the amount of ground fuel before and after the fire using downed woody debris and Brown fuel transects 1974 In this study I test the hypothesis that in areas of my study site with significantly less ground fuels after a prescribed burn than before the burn correlates with greater increase in tree diameter than would otherwise occur I am also testing the hypothesis that trees in the watershed subjected to a prescribed burn will exhibit a more positive response in radial growth than occurs in the control watershed In essence I am asking if fire is beneficial to the trees in a the blue oak savanna of the Sierra Nevada Foothills Methods My study is a subset of a larger project conducted in the UC Berkeley department of Environmental Science Policy and Management which attempts to answer the NPP question in the blue oak systems at my site Forest ecologist John Battles and rangeland ecologists Barbara Allen Diaz and James Bartolome focus on using a continuous ecosystem approach which House et al 2003 recommends for addressing the three conundrums of savanna ecosystems By examining the response of trees to fire in this
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