Bruca G, Marcot, USDA ForestService, Six BrversNat onal Forest, 507 F StreetEureka, California 95521' Limnology,Vegetation, and Classificationof CoastRange Slump-formed Ponds Abstract Slunp-formed ponds afford scarceriparian and aquatic habitats in north co{sral California. Thi6 study prolides i.tormarion and a classificarionsysten for their nanagement.Iourteen slunp-forned pondswere studied in rhe CoastRange ofno.th{eslern California during 1975-I9?6for linnological and vesetarion characrerisrics.The ponds areraeed 2.4 m naiimun depth and 0.56Ia sudacearea. Subsu.face conrours and hypsographiccunes suggestedvarious stages of basinfi -in. Warer quality(dissolved oxysenand t€nperature) and ih€ presenceof algae species(Nygaard's trophic index) provided evidencerhar the ponds wer€ typically mesotrophicto eurrophic. Algal, subnergenl, emergent,and ripa.isn vascular planr specieswere id€.tiai€d. Ponds werecla$ifi€d basedon wat€r perna.ence (eph€meral,aststic, and stable)and succ€ssionalsrase (desre€ ofbasin fill,in). Pond classescorresponded to unique conbinations of limnological and vegetation characreristics.The pond classificarionsystern is useful for guiding nanagement acriviries to rehabilitate, naintain, and enhanceriparian and aquaric habirals associated Introduction pondswere identified frorn aerialphotos (scale Little is known of the physical and biological l:15,840)and from field surveysand werechosen characteristicsof slump-formedponds in the to representa cross-sectionof physicaland bio- CoastRange of the Pacificstates, although rhe logical conditions.The steepslopes on which the total area of wetland and fresh-wateraquatic pondswere found weretypically composed of un- habitatsis relativelysmall and hasbeen declin- stableregolith and mass-vastingwas fairly com- ing in recentyears in the west(e.g., Sands and mon throughout the region. Howe l9??). Specifically,the riparian habitat in The generalstudy area is characterizedby the coastalfoothills of HumboldtCounty in the warm dry summersand cool wet winters.Average CoastRange of northernCalifornia comprises 0.2 annual rainfall is 64-165 cm; averagemonthly percentof the county'stotal acreage,but is the precipitation is as high as 2540 cm during mostvaluable habitat as a concentrationpoint Novemberto January,and as low as 0-2 cm dur- for many floral and faunal species(California ing July and August (data from Lower Triniry Departmentof Fishand Game1965, Thomas el RangerDistrict office,Six RiversNational Forest, al. 1979). Willow Creek,California). Mean minimum month- This study was promptedby the need for ly temperaturesrange 0-4oCduring winter and understandingthe limnologicaland vegetational 7-1l"C duringsummer: and maximumrempera- characteristicsof Coast Range slump-formed tuies range from 7-l3oC during winter and pon-dsas a basisfor developingmarlagemenr 30-35oCduring summer.Summer veather during criteria.The objectivesof the studywere to (l) the study was drier and warmer than average. describephysical and chemical limnological All ponds were within the Mixed Evergreen characteristics,(2) describeaguatic and riparian Forest with Chinquapir:'(Casta.n opsis chrysoplrylln) vegetation,and (3) develop a classification or Rhododendron(ft hodod.end.ron macrophyllum) system,based on limnologicaland vegetation rcgelaliontypes (Kiichler 197?). Dominant tree characteristics,for describingand predicting speciesin thesetypes arc Douglas-fir(Pseudotsuga both physicaland biologicalattributes. menziesii),tanoak (Lithocarpusdensiflora) and Study Area Pacific madrone(Arbutus menziesir. During 1975-1976,l7 pondswere located and Methods studiedon Six Rivers National Forest in the CoastRange of northwesternCalifornia. The LimnologicalSunteys. Pond maximum length (l), breadth, surface area (A), and shorelinelength 'Currenr address:USDA ForesrService, Mr. Hood National (L) weremeasured on all pondswith a planimeter Forest, 2955 N.V. Division St., Cresham,Oreson 97030 on aerialphotos or on surfacemaps developed NorthwestScience, Vol. 64, No. t, 1990 55 in the field by using an alidade and plane table surface. Algae were identified to speciesand (Welch 1948,Lind 1974).Mean breadth(A/1) and trophic state of each pond was indexed by the shorelinedevelopment indices (L/2.1[zA]) were relativeproportions of variousspecies in the calculatedfor eachpond. The shorelinedevelop- samples(Nygaard 1949). ment index describesshape of eachpond by com- Submergenls.emergenls. and riparian rege- paringthe shorelinelength to a circlewith the tation weresampled during summerat six ponds samearea as the pond. The smallestpossible (Underwood,Bushwack, Primal, GreaterTwin, value is 1.0, representinga circle, and index LesserTwin, and DuckweedPonds) chosen to valuesincrcasp as the shapebecomes more ir- representa spectrumof depth, surfacearea, (Cole regular 1975,Lind 1974). degree of basin fill'in, and lrater permanence. Maximum depth and percent relatiye depth Sr.:bmergentvegetation vas sampledin each of all pondswere measured by soundingsfrom of the six pondswith B0 scoopsof a rake at even a raft. Hypsographiccurves were estimated from inteNalsalong two transectsacross each pond. benthiccontours drawn for four pondsrepresent- Frequencyof each specieswas determined(no. ing early and late stagesof basin fill-in (Bee,Red scoopsa specieswas observed in/80 total scoops) Mountain,Onion, and BrokenRib Lakes).Cal- and a descriptive scale for frequency of sub- culationsof morphologicpararneters followed mergentswas used(available from author). For Cole(1975) and Welch(1948). Poles marked in purposesof this study, duckweedswere con- 0.2 m intervalswere placedin eachpond and sidered as submergentsbecause they occurred water \,yasmeasured by recording Permanence in the scoopsamples. Density (no. stems/m2) of changesin surface elevations biweekly during eachstand of emergentvegetation was estimated 1975 and 1976 summersand bimonthly during by averagingthe number of stemswithin a wire the l9?5-1976year. Sediment depth was probed frame(1 x I m) placedrandomly at 20 locations in all pondsduring summer1975 with a tele- within eachemergent sland. scopicpole. Riparianvegetation was sampled by use of Temperatureand dissolvedoxygen (DO) were fixed-areaplots, the sizeof whichwas determined rnonitoredat 0.3m intervalswith a portableDO from species-areacurves derived from nested andtemperature meter (Model l0l0 DeltaScien- quadrats(Dosting l95B). Plot tific Corporation)four times during late summer shapeswere rec- tangular(sides 3:1, the longerrunning parallel 1957 in four ponds representingvariable or to the shoreline),Twenty plots were distributed stablewater conditions, The meter wascalibrated evenlyaround each shoreline immediatelybefore each measurement.Five and vegetatronrtas assessedby using the Braun-Blanquetcover- watersamples were taken at randomdepths and abundancescale (Mueller-Dombois and Ellenberg locationsfrom eachpond and analyzedin the Six l9?4). Percentfrequency was calculatedand RiversNational Forest laboratory for pH, con- modalcover determined of speciesover l0 per- ductivity,and rurbidity (Model7 pH Meter, Corn- cent frequent. ing ScientificInstruments; Model R83 Conduc- tivity Meter,Bechman Instruments; Model 2100A Quantitativedescriptions of submergent, Turbidimeter,Hach ScientificEquipment). emergent,and shorelinevegetation from the six legetation Sampltng. Algae were sampled pondswere supplemented by qualitativeobserva- during summer at four ponds (Primal Pond, tionsof pondbasins and vegetation made at all BushwackPond, Sucker Lake, and Big Lake) 17 ponds. Descriptionsincluded pond basin chosenbecause they variedgreatly in physical topography,and frequencyand coverof vegeta- characteristics(especially water permanence)and tion speciesestimated by eye. would provide a vide variety of species.The Pond Chssification.The purposeof develop- pondssampled represented the wide range of ing a classificationsystem was to identify unique ponds (except for the early successional structural and floristic attributes of different ephemeralclass) included in the classification types of ponds to help predict physicaland systemthat was ultimately developed.Three biological responsesto managementactivities algaesamples were taken from each pond by and guide managementstrategies. Classification planklonnet tow, squeezingsfrom submergent basedon vegetationcharacteristics alone was not flora (tychoplankton),and skimming the water sufficient for this purpose. The intent was to 56 Marcot devisea systemby which vegetation character- ly and late stages)of ephemeralponds correlated isticscould be predicted from other, physicalat- with diagnosticcharacteristics. Limnological and tributesof the ponds. vegetationcharacteristics were related to each To devisethe classificationsystem, results of of the pond classes. the vegetationsamples and qualitative descrip- tionsof all pondswere related to the chemical, Resultsand Discussion physical,and trophic attributesof the ponds. Lirnnology Sincemost ponds were mesotrophic to eutrophic, trophic state was not a helpful criterion to dis- The ponds were likely formed by the mass- tinguishamong ponds. Water quality(pH, con- wastingprocess of soil creep,a slumpagethat ductivity, turbidity, dissolved oxygen content) created small basinsthat filled with snow-melt, seemedto vary in responseto physicalconditions seepsprings, or runoff. On average,the ponds of thepond basins and associatedvegelation. measured133 m maximumlength, Tl m maxi Ultimately,the pondswere classified based mum breadth,and 38 m averagebreadth