Improving Fire Hazard Assessment at the Urban-Wildland Interface ...

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Association (NFPA 299). In contrast towildland areas, this fuel matrix requiresactive homeowner involvement in firehazard mitigation. This necessity hasresulted in regulations governing thelandscaping practices by private landownersin the high fire hazard areas of California(CA PRC 4291). Designed with theimportance of fuels reduction and structuresurvivability in mind (Brown 1994, Cohen1995, Tran 1992, Foote 1991), PRC 4291requires defensible space for at least 10meters around the home. It limits ahomeowner’s choice of plant species,density, and placement and regulatesmaintenance practices such as pruningtrees and removing ladder fuels.Though compliance with PRC 4291 mayincrease fire safety, the law does notrecognize (1) the variability in the individuallandscaping preferences that people have,or (2) the impact of neighboring parcels on ahomeowner’s fire hazard. Residents at theUWI have unique, individual sets of valuesand preferences that are reflected in thelandscapes they create and maintainaround their homes. These values oftenconflict with the principles of fire safety butproperty owners resist fire-safe regulationsif they detract from what is valued in thelandscape (Manfredo 1990, Abt 1991,Bailey 1991, Cortner 1991, Foote 1991,Smith 2001, Hodgson 1993, Winter 2000).In some communities, the combination ofthese two problems – small lot size andlandscape preferences – poses a significantbarrier to effective individual and communityfire hazard mitigation.This report describes a fire hazard analysisconducted on private, developed lots inSouth Lake Tahoe, California. South LakeTahoe is a high fire hazard UWI communityin Northern California where many of thedeveloped lots are noncompliant with PRC4291 even though there is active agencyoutreach and public support of fuelsreduction on undeveloped lots (Garrett,pers. comm., Harcourt, pers. comm.). Firehazard was assessed according to thestandards in NFPA 299, compliance withPRC 4291, construction materials of thehome, irrigation practices, and the influenceon a parcel’s fire hazard by its immediateneighbors.Results indicated that the overall fire hazardscore for the city was relatively low becauseof infrastructural components such as goodroads, water availability, signage, andfirefighting resources. Analysis of thecomponents that involve homeowner choiceonly (e.g. defensible space, maintenance,irrigation, and construction materials)indicated limited individual, parcel-scale firehazard mitigation efforts.Study siteSouth Lake Tahoe has approximately24,000 inhabitants and is located on thesouth shore of Lake Tahoe, adjacent to theNevada border. The greater Lake TahoeBasin extends across 88,000 hectares intwo states (California and Nevada) and fourcounties (El Dorado, Placer, Douglas andNevada). Its elevation ranges fromapproximately 1900 m at the surface of thelake to about 3300 m at Freel Peak.Historically, fires in the Tahoe Basin wereprobably low and medium intensity surfacefires, occurring every 15 – 25 years andconsuming mostly light surface fuels, rarelybecoming stand-replacing events (Skinnerand Chang 1996). Eighty-five years of firesuppression in the basin (Murphy andKnopp 2001) combined with recent,prolonged drought conditions and extensivebug-kill have led to a build up of highlyflammable, hazardous fuel conditionsthroughout the area.The dominant conifer species in the lowermontane zone is ponderosa pine (Pinusponderosa), with some white fir (Abiesconcolor), incense cedar (Calocedrusdecurrens), and sugar pine (P. lambertiana).The upper montane zone (approx. 2000 –3000 m) is dominated by Jeffrey pine (P.jeffreyi) and also contains red fir (A.2
magnifica), white fir, western white pine (P.monticola) and some pure stands oflodgepole pine (P. contorta). In thesubalpine zone (above 3000 m) speciesinclude whitebark pine (P. albicaulis) andmountain hemlock (Tsuga mertensiana)(Manley and Schlesinger 2001).The average January temperature for thebasin is slightly below 0° C, the averageJuly temperature is approximately 16° C,and the average annual precipitation is 74cm. Average annual snowfall ranges from2.5 m at the elevation of the lake to almost 9m in the mountains. At lake level, there areon average only 70 – 100 frost-free daysper year (U. S. Environmental Data Service2000).Archaeological evidence suggests thathuman habitation of the Tahoe Basin beganwith the ancestors of the Washoe NativeAmericans, who entered the Basin after theSierran glaciers retreated 8,000 to 9,000years ago. The first non-Native settlersarrived in the basin after the discovery ofgold and silver in nearby Virginia City,Nevada. Early industry included logging,ranching, grazing and fishing. By the earlytwentieth century, less than half of the presettlementforest in the Tahoe Basinremained. While timber harvestingdecreased, grazing and ranching continuedbecause of the need for farm products forthe basin’s expanding population.Management agencies and consortiumswere developed in the Lake Tahoe Basin tomitigate the negative ecological impacts ofthe basin’s growing population. Among themost visible are the Tahoe RegionalPlanning Agency (TRPA), the USDA ForestService’s Lake Tahoe Basin ManagementUnit (LTBMU), and Tahoe Re-Green. TheTRPA is a powerful regulatory organizationwhose primary objective is to develop landuse and management standards thatmaximize environmental health and mitigatenegative environmental impacts fromdevelopment (Murphy and Knopp, eds.2000). Since the early 1970s, TRPA hasprohibited development on environmentallysensitive parcels and has regulated privatelandowners’ management of their ownparcels. To compensate landowners, theLTBMU and the California State TahoeConservancy have purchased many ofthese lots. The LTBMU also plays an activerole in fuel management on theundeveloped urban lots owned by theForest Service. Tahoe Re-Green is aninteragency consortium that aims to educateresidents and help them reduce fire hazardby removing fuels on privately owned land.MethodsSampling sites were chosen from apopulation of approximately 6,500 singlefamilyresidential parcels. These parcelswere stratified into low, medium, and highcanopy cover and into low, medium, or highdensity residential. A proportional allocationmethod was used to determine the numberof parcels to be sampled within eachstratum. In total, 102 parcels across the citywere sampled. The vegetation andstructural characteristics of each parcelwere measured and mapped.The city was divided into six neighborhoodsbased on observed differences invegetation, lot, and building characteristics(Fig. 1) (de Jong, in review). The initialocular classification was refined throughstatistical analysis for homogeneity in eachof the defined neighborhoods. Theboundaries of each neighborhoodencompass built areas within city limits andexclude unbuilt areas such as parks andgolf courses. Major roads defined theboundaries between adjacentneighborhoods.Neighborhood 1 was the Tahoe Keys,characterized by wide streets, canals, large,new homes and planted exotic vegetationand turf grass. There was no significantslope on any of the parcels found in thisneighborhood. Neighborhood 2 – 5 weresimilar to one another in terms of smallparcel and home size. Their vegetation was3
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