TreatmenteffectsonstructureandfirebehaviorintheUncompahgreMesasForestRestorationProject–March2014

Figure1.MapofUncMesaunit#1andstudysite

Summary• WefoundtherestorationtreatmentintheUncMesarestorationprojectreducedhorizontalandverticalstructuralcomplexity,thoughpost-treatmentstructurewasstillfarfromhomogeneous.

• Thetreatmentwaseffectiveatreducingfirebehavior;effectivenessincreasedwithhigheropenwindspeeds,despitegreaterwithin-canopywindspeedspost-treatment.

Recommendations• Considertradeoffsoffirehazardandstructuralcomplexityobjectives.

• Adoptmetricsofcomplexitytoenableadaptivemanagement

• Definetargetrangesofcomplexitytosteertreatmentsawayfromshiftstowardshomogeneity

• Reducesurfacefuelloadstoleveragegainsmadealreadybythinning.

Ponderosapine(Pinusponderosa)forestswithintheUncompahgreNationalForest,likemuchofthewesternUnitedStates,haveundergoneashiftfromamosaicpatternconsistingofindividualtrees,patchesandopeningsthatexhibitedavarietyoftreesizestoamoredense,homogeneousforeststructure.Thesechangeshaveresultedinanincreasedconcernoverthepotentialforalteredecologicalfunctions,suchasincreasedpotentialforcrownfires.Inresponsetothisconcern,restorationtreatments,suchasthoseapartofUncompahgrePlateauCollaborativeForestLandscapeRestorationProject,seektoenhancestructuralcomplexity,andmitigateundesirablefirebehavior.However,duetotraditionalviewsofstandmanagementandspatially-inexplicitstanddynamicsandfirebehaviormodelstheimplicationsofstructuralcomplexityarenotfullyevaluated.

Studyobjectives

Thisstudyutilizedfield-collecteddata,spatial-statisticalmethodsandthreedimensionalphysicsbasedfirebehaviormodelstoinvestigaterestorationtreatmenteffectson1)verticalandhorizontalstructuralcomplexityatboththestand-levelandpatch-level,and2)firebehavior,acrossarangeofwindspeeds.

Approach

Duringthesummer2012,weestablishedasingle200mx200mplot(~10acres)withinunit#1oftheUncMesarestorationproject(Fig.1)andstem-mapped,andmeasuredallstumpsandtrees(≥4.5fttall(Fig.2)).Pre-treatmentforeststructurewasrecreatedusingacombinationoflinearregressionmethodsandadditionalfieldsamplinginadjacentstands.Structuralcomplexityinboththehorizontalandverticaldimensionswasevaluatedatboththestandandpatchlevelsusingcommonspatially-explicitmethodologies(Fig.3).

PotentialfirebehaviorwassimulatedbypopulatingtheWildland-urbaninterfaceFireDynamicsSimulator(WFDS)withourfieldcollecteddataforthepre-andpost-treatmentforests.WFDSisaphysics-basedfiremodel,developedbytheNationalInstituteofStandardsandTechnology,designedtosimulatethespatially-andtemporally-dynamic

Figure3.Frameworkofstructuralcomplexityusedinthisanalysis:a)thespatialpatterningoftreesatthestand-level;b)changesinpatchsizedistribution;c)canopyroughness;andd)thevariationintreesheightsamongpatches.

Figure2.Stem-mapoftreespre-treatment(above)andpost-treatment(below),leveldtomeasuredcrownradiiinUncMesasunit#1plot

interactionsbetweenfire,vegetationandwindflow.Wesimulatedfirebehaviorpre-andpost-treatmentunderfouropenwindscenarios(5,9,20,and30mph)withtypicalmid-summerdeadandlivefuelmoistures.Foreachsimulation,weestimatedthemeanrateofspread,meanfirelineintensity,andpercentofcanopyconsumed.

Table1.Analysesofstructuralcomplexity

Pre Posta)Stand-levelhorizontalcomplexityPattern(random,agg.,unif.) Agg. Agg.*

b)Patch-levelhorizontalcomplexityAerialcover(%) Individualtree 4 4

Patches 39 24Openings 57 72Patchmetrics Patchsizecomposition Small(1-5trees) 22 44 Medium(6-10trees) 13 21

Large(11-20trees) 31 17 Verylarge(20+trees) 34 18c)Stand-levelverticalcomplexity

THindex 0.57 0.54 d)Patch-levelverticalcomplexity

CVHT 0.41 0.36*Post-treatmentwasmoreuniformthanpre-treatmentAgg.,aggregated;unif.,uniform;CVHT,

Findingsanddiscussion

Followingtreatment,structuralcomplexitywasdecreasedasmeasuredbyashifttowardsmoreuniformityoftreepatternatthestand-level,reductioninstand-levelcanopyroughnessandthetreeheightdiversitywithinapatch(Table1).Thissuggeststhatthetreatmentresultedinanoveralldecreaseinstructuralcomplexitywithin3ofour4measures.However,thetreatmentdidresultinareductionintheaveragepatchsizeandadecreaseinthetotalcanopycoverofpatches,indicatingareductioninthenumberoflargepatchesthusfavoringthecreationofamatrixofindividualtrees,patchesandopenings.Althoughthetreatmentdidlargelyresultinsimplificationofstructuralcomplexity,thepost-treatmentstructurestillmaintainedsomedegreeofheterogeneityacrossallmeasures.

Wesuggestmanagersadoptfeasibleandqualitativeorquantitativemethodstoassesscomplexity.Asidefromenablingsettingandevaluatingofstructuralrestorativegoals,thisprovidesameanstoconsiderthetrade-offsofmeetingmultipletreatmentobjectiveswhenmarkingorremovingtrees.Forexample,wepostulatethereductioninstructuralcomplexityisduetoaconflictinimplementationbetweenecologicalrestorationandfuelshazardmitigation.Theincreasesintreeheightandcanopybaseheight(Table2)suggestremovalofladderfuels,whichwouldresultindecreasedaggregationandtreeheightdiversity.

Followingtreatment,firebehaviorwasreducedacrossallwindscenariostested(Table4).Treatmenteffectivenessalsoincreasedwithhigheropenwindspeeds,despitehigherwithin-canopywindspeedsfollowingtreatment(Fig.3).ThereductionofcanopybiomassandsurfacefuelsdiminishescrownfireactivityasseeninFigure4,thusloweringrateofspreadandfirelineintensity.Itshouldbenotedthatprojectedfirebehaviormaystillbegreaterthandesired.Thisstudyextendsto6othersitesacrosstheRockyMountainsandColoradoPlateau;simulationsacrosssitessuggestreducingsurfacefuelsisthemosteffectivemethodatreducingfirebehavior.

Acknowledgements

WethankLarryHuseman,andtheColoradoForestRestorationInstituteforaidinfield-sampling,aswellasMattTutenforidentificationofourfieldsite.FundingforthisprojectwasprovidedforinpartbyJointFireScienceProgram(JFSP)project13-1-04-53,theRockyMountainResearchStation,ForestService,U.S.DepartmentofAgricultureandtheNationalFirePlan.

mediancoefficientofvariationintreeheightswithinapatch

Table2.Summaryofnon-spatialstandstructurepre-andpost-treatmentinUncMesaUnit#1

Treatmentstatus Pre PostTPA 203 126QMD(in) 10.8 10.5BA(ft2/acre) 135 77CBH(ft) 20 22.3HT(ft) 64.6 83.7Surfaceload(tons/acre) 5.4 4.7Speciescomp. 87%PIPO,

6%POTR,7%PIPU,1%QUGA

87%PIPO,7%POTR,6%PIPU,1%QUGA

TPA,treesperacre;QMD,quadraticmeandiameteratbreastheight;BA,basalarea;CBH,meancanopybaseheight,HT,90th%iletreeheight;speciescodesfollowNRCSPLANTSnomenclature

Figure3.Windspeedprofilesfortwoopenwinds(5and30mph)pre-andpost-treatmentinUncMesaunit#1,simulatedusingWFDS.

Figure4.TimeseriesofWFDSsimulatedwildfireinthehighestwindscenario(30mphopen)

fortheUncMesaunit#1before(left)andafter(right)treatment.

Table3.ResultsoffiresimulatedbyWFDSinUncMesaunit#1,pre-andpost-treatmentacrossfourwindscenarios.Openwindspeed

Rateofspread

Firelineintensity

Canopyconsumed

(mph) (ch/hr) (kW/m) (%) pre post pre post pre post

5 107 88 21081 12726 69.7 51.29 157 154 35335 19256 67.3 46.520 289 221 70800 29934 78.1 51.630 320 251 108460 37118 80.3 52.9

Thissummaryisproducedfromastudyspanning7studysitesacrosstheRockyMountainsandColoradoPlateauconductedby:JustinZiegler(CSU),ChadHoffman(CSU),andMikeBattaglia(USDS-FSRMRS).

Formoreinformation,contactJustinat:zieg9479@rams.colostate.edu