record of stand response derived by comparing all growth ringsdeposited in the years prior to fertilization to the years immediatelyafter, allowed for further description of the timing and magnitude of thenitrogen response. Analysis of WUE obtained from these rings helpexplain the interaction between the use of a finite water supply andnitrogen fertilization. These results are exciting, not only because thistype of physiological analysis has never been quantified over this largea geographic region, but also because significant differences in LAIhave been detected 15 years after the initial fertilization.

Variability of Pretreatment Soil Nitrogen Pools in Large-ScaleLong-Term Forest-Ecosystem Experiments

P S Homann (Oregon State University, Corvallis, OR 97331-7501; ph.541-737-6571; fax 541-737-1393; Internet homannp@ccmail.orstedu);B T Borman (USDA Pacific Northwest Research Station, Corvallis,OR 97331-8550; ph. 541-750-7323; fax 541-758-7760; Internet:bormannb®ccmail.orstedu); J R Boyle (Oregon State University,Corvallis, OR 97331-5703; ph_ 541-737-4036; fax 541-737-3049;Internet: boyle@fsl.orstedu) (AGU Sponsor G E Grant)

Low nitrogen availability limits tree growth in many forests of thePacific Northwest, USA. Forest management practices have thepotential to alter soil N pools and other soil properties, which couldinfluence future forest productivity. This concept is being examined inDouglas-fir forests of Washington and Oregon by the Long-TermEcosystem Productivity program, a cooperative effort among federaland state organizations. At each of four Integrated Research Sites, alarge-scale, multiple-rotation experiment is manipulating vegetationcomposition and coarse woody debris in a three-by-two factorial design.Each 6-ha treatment plot and a control are replicated in three blocks.

At the Siskiyou Integrated Research Site in southwestern Oregon,pretreatment mineral soil N mass (kg N per square meter to 30 cmdepth) was determined by quantitiative coring. Between-plotpretreatment differences occurred on two blocks, and soil N massdiffered by as much as 40% between plots within a block. Thedifferences were created by various combinations of between-plotvariation in the three properties from which N mass is calculated: soilN concentration, soil bulk density, and coarse-fragment volume. Thepretreatment values can be used as Gamines to increase the sensitivityof assessments of treatment effects on soil N mass and other ecosystemproperties. This study demonstrates the importance of thoroughpretreatment evaluation of soil properties in forest-ecosystemexperiments.

Nitrogen Fluxes in Experimental Watersheds inWestern Oregon

K L Vanderbilt (Department of Forest Science, OregonState University, Corvallis, OR 97331; S41-750-7393;vanderbkeccmail.orst.edu). K Lajtha (Department ofBotany and Plant Pathology, Oregon State University,Corvallis, OR 97331; 541-737-5674;lajthakdbcc.orst.edu ; and F J Swanson (USE'S, PacificNorthwest Research Station, Corvallis, OR 97331;541-7S0-7355; swansonsfsl.orst.edu )

Long-term precipitation and stream water chemistrydata from control and logged watersheds at the H.J.Andrews Experimental Forest, Oregon were analyzed toevaluate biogeochemical differences resulting fromdisturbance, differing successional stages ofvegetation, and varying nitrogen inputs. Nitrogenflux was closely tied to the hydrologic cycle.Nitrate export (kg/ha) in .stream water was elevated ina treated watershed during the six years followinglogging when diminished evapotranspiration resulted inincreased stream discharge. Export of dissolvedorganic nitrogen from a treated watershed exceededthat from a control watershed for five years afterdisturbance. No difference was detected in output oftotal organic nitrogen between watersheds. Seasonaland annual patterns of nitrogen yield in thisnitrogen-limited ecosystem, as dalculated by nitrogen

yield (nitrogen output in stream water)/(input fromlichen and alder nitrogen fixation and dry and wetatmospheric deposition), differed from patternsobserved in watersheds with elevated nitrogen inputs.

EVALUATION OF THE EFFECTS OF FOREST MANAGEMENTON WATER QUALITY IN THE SOUTH UMPQUAEXPERIMENTAL FOREST WATERSHEDS, OREGON

If.„Srmae, W.E. Miller, T. Shiroyama, and M. Knittel (GreeneEnvironmental Services, 33180 Dorset Lane, Philomath, OR, USA97370-9555; ph. 541-754-4773; fax541-754-4799; intemetgreenejo(a)ucs.orstedu)

The impact of forest management practices upon water quality wasexamined in second order streams in the South Umpqua ExperimentalForest An undisturbed and three harvested watersheds were evaluatedby laboratory algal assays, in situ periphyton productivity, benthoscollection, and bacteria plate counts.

Samples from the total clear cut watershed gave three times higher .NO2+NO3-N concentrations than those collected from the patchclearcut and the shelterwood thinned watersheds. Nitrogen was theprimary limiting nutrient in each of the watershed streams asdetermined by 78% of the algal assays using Selenastrumcapricornutum, while phosphorus and trace elements were dividedequally as primary limiting nutrients in the remaining 22% of thesamples assayed.

Fecal coliforms and fecal streptococci numbers increased after cattlebegan grazing in the watersheds. The greatest increase in bacterialpollution occurred in the total clear cut watershed, followed indescending order in the undisturbed, patch clear cut, and shelterwoodthinned watersheds. This ranking of water quality impact by forestmanagement practices matches that found by laboratory algal assaysand in situ periphyton standing crop measurements.

Impact of nitrogen deposition on nitrogen cycling in forests: asynthesis of NITREX data

p Gundersen (Danish Forest and Landscape Research Institute,Hoersholm Kongevej 11, DK-2970 Hoershohn, Denmark; ph.+45-4576-3200; fax +45-4576-3233; Internet:fslpgu(a)rmidhp.uni-c.dk); A Tietcma, C J Koopmans (University ofAmsterdam, Nieuwe Prinsengracht 130, NL-1018 VZ Amsterdam,Netherlands); 0 J Kjnaas (Norwegian Forest Research Institute,I-Igskoleveien 12, N-1432 Arts, Norway); B A Emmett (Institute ofTerrestrial Ecology, Deniol Rd, Bangor, Gwynedd LL57 2UP, UK)

Impact nitrogen (N) deposition was studied by comparing N fluxes, Nconcentrations and N pool sizes in vegetation and soil in five coniferousforest stands. The sites span a N deposition gradient from 13 to 59kgN/ha/yr. Further, results from 4-5 years of NH4NO3 addition (35kgN/ha/yr) at three low deposition sites and 6-7 years of N removal(roofs) at two high deposition sites were included in the analysis.Significant correlations were found between a range of variablesincluding N concentrations in foliage and litter, soli N transformationrates and forest floor characteristics. A principal component analysissummarized these variables to one variable interpreted as an indicatorof site N status. Site N status increased with N deposition with theexception of one site naturally rich in N. Nitrate leaching wassignificantly correlated with N status but not correlated with Ndeposition. Forest floor mass and root biomass decreased with increasedN status. Characteristics of the mineral soil were not correlated withvegetation and forest floor variables. High C/N ratios in the mineral soilat the high N deposition sites suggest that the mineral soil pool changeslowly and need not change for N saturation to occur. The of changes

32

111•In

Forested Catchments

September 16-20, 1996Sunriver, Oregon

Conveners: M. Robbins Church, US EPA, National Health andEnvironmental Effects Research LaboratoryCharles T. Driscoll, Syracuse University, Department ofCivil and Environmental Engineering

Have you considered convening a

CHAPMAN CONFERENCE?Chapman Conferences are topical meetings designed to permit organized and in-depth exploration ofspecialized subjects in a manner not possible at large meetings. They encourage disciplinary andinterdisciplinary focus on special problems and provide timely encouragement for the development of newlyemerging research fields and problem areas, or for revisiting areas where recent developments warrant a newlook. The typical size of Chapman Conferences is around 125 participants, although successful meetingshave been held with as few as 50 attendees. An attempt is made to encourage significant attendance bygraduate students and foreign scientists through travel grants and, in the case of students, reducedregistration fees.

Recent Chapman Conferences have addressed such topics as....

Circulation of the Intra-Americas SeasMeasurement Techniques for SpacePlasmas: What Works and What Doesn'tLong Lava FlowsCoronal Mass Ejections: Causes andConsequencesWater Vapor in the Climate SystemBiomass Burning and Global ChangeMagnetic Storms

Hydrogeologic Processes: Building andTesting Atomistic-to Basin-Scale ModelsScrutiny of Undergraduate GeoscienceEducation: Is the Viability of the Geosciencesin Jeopardy as we Approach the 21stCentury?Aqueous Phase and Multiphase Transport inFractured RockCrater Lakes, Terrestrial Degassing Hyper-AcidsFluids in Environment

Thomas Torgersen, Chapman Conference Chairman, is prepared to assist in the development of ChapmanConference proposals. He would be happy to discuss possible topics and any aspect of conferenceorganization with any AGU member. Many successful Chapman Conferences have been convened by recentPh.D's especially when working with a more senior scientist as co-convener. Thomas Torgersen (Universityof Connecticut, Department of Marine Sciences) can be reached at 203-445-3441 or e-mailtorgers@uconnvm.uconn.edu .

AGU also has aCHAPMAN CONFERENCE GUIDE

which discusses all aspects of Chapman Conference organization, including allocation of responsibilitiesbetween convener(s) and AGU staff (generally, conveners handle the scientific program; site planning andother logistical arrangements are handled by staff).

The guide is available upon request from AGU Meetings Department, 2000 Florida Avenue, N.W.,Washington, DC 20009; phone: 202-462-6900 (in D.0 or outside North America) or 1-800-966-2481 (toll-free in North America); fax: 202-328-0566; or e-mail: kpak@kosmos.agu.org.