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    <big><big><b>***PHD Seminar***</b></big></big><br />
    <br />
    <big><b>Erin Hanan</b></big><br />
    </p><p class="MsoNormal" style="text-indent:0in;line-height:normal">Thursday,

      December 10^th,  8:30am </p>
    <p class="MsoNormal" style="text-indent:0in;line-height:normal">Bren
      room 1424<br />
    </p>
    <p class="MsoNormal" style="text-indent:0in;line-height:normal">******************************************************************************************************************************************************<br />
    </p>
    <p align="center" class="MsoNormal" style="text-align:center;text-indent:0in;line-height:normal">Biogeochemical responses to fire in coastal
      chaparral
      ecosystems</p>
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    <p align="center" class="MsoNormal" style="text-align:center;text-indent:0in;line-height:normal">Erin J. Hanan</p>
    <p align="center" class="MsoNormal" style="text-align:center;text-indent:0in;line-height:normal"> </p>
    <p class="MsoNormal" style="line-height:normal">Fire is a major
      restructuring
      force in chaparral and other Mediterranean-type ecosystems.
      Following fire,
      heavy winter rains can leach nitrogen (N) into streams,
      particularly from
      slopes that have been denuded. The extent to which N is
      transported from burned
      slopes to streams depends on how rapidly soil microbes metabolize
      N into mobile
      forms such as nitrate and how rapidly recovering plants take up
      mineral N. <span style="mso-bidi-font-weight:bold">This
        dissertation research combines empirical
        analyses and modeling to evaluate how ecosystems recover in
        the years following fire and how this affects the rates at which
        N is leached
        into streams and from watersheds. </span></p>
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        bold"><br />
      </span></p>
    <p class="MsoNormal" style="line-height:normal"><span style="mso-bidi-font-weight:
        bold">Fieldwork focused on how N-retention mechanisms
        counterbalance post-fire
        mobilization processes, a point that has not been well studied
        in chaparral
        ecosystems. </span>In burned sites, nitrification was
      significantly enhanced
      relative to rates measured in unburned sites, however ephemeral
      herbs
      established quickly, immobilizing large amounts of N relative to
      annual net N
      mineralized. Microbial biomass on the other hand decreased
      substantially in the
      first growing season, and remained low through the following year.
      Laboratory
      incubations revealed that nitrification<span style="mso-bidi-font-weight:bold">
        increased most rapidly following ammonium addition. When
        ammonium was
        sufficiently high, pH determined the relative proportion of
        inorganic N that
        was nitrified, while char did not have a strong impact on N
        cycling. </span>Modeling
      simulations suggest that N <span style="mso-bidi-font-weight:bold">export is
        highest when fire is followed by drought. This occurs because
        dry conditions
        prolong the period during which nitrification is decoupled from
        plant uptake. Pre-fire
        drought also increased N loss relative to average conditions
        because it reduced
        the recovery rate of post-fire vegetation. These results suggest
        that climate
        can regulate N balance by influencing how quickly plants “turn
        on” and begin to
        take up nutrients mobilized by fire.</span></p>
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</p></span></div><br /><br />--<br signature="separator" /><div align="" left""=""><font face="Tahoma" size="2"><b>Jenny Dugan</b><br /></font></div><font face="Tahoma" size="2">Marine Science Institute<br />University of California<br />Santa Barbara, CA 93106-6150<br />Phone: 805-893-2675</font><font face="Tahoma" size="2"><font #191970""="" color=""><font color="#000000"><br />email: j_dugan@lifesci.ucsb.edu<br /></font></font></font><font face="Tahoma" size="2"><a href="" http:="" index.html""="" sbc.lternet.edu="">http://msi.ucsb.edu/people/research-scientists/jenny-dugan </a></font><font 2""="" face="Tahoma" size=""><font #191970""="" color=""><font size="2"> </font><br /></font></font><font color="#2f4f4f" face="Tahoma" size="2"><a href="" http:="" index.html""="" sbc.lternet.edu=""><font color="#000000">SBC LTER:</font> </a></font><font face="Tahoma" size="2"><a href="" http:="" index.html""="" sbc.lternet.edu=""> http://sbc.lternet.edu/index.html</a></font><font face="Tahoma" size="2"> <br /></font></span>