<strong>Cal</strong>i<strong>for</strong>nia Exotic Pest Plant Council1997 Symposium Proceedingsexhausted by germinati<strong>on</strong> and mortality. Nei<strong>the</strong>r will occur at appreciable rates without procedures to enhance<strong>the</strong>m - dormancy of most seed can <strong>on</strong>ly be broken by heat, and dormant seed is l<strong>on</strong>g-lived based <strong>on</strong> in<strong>for</strong>mati<strong>on</strong>about closely related species. Scotch broom seeds remain viable <strong>for</strong> at least 80 years (Turner 1933), and manyo<strong>the</strong>r legume seeds are known to have much greater l<strong>on</strong>gevity (Baker 1989). Since <strong>the</strong>re is no o<strong>the</strong>r practicablemeans of treating seed to reduce <strong>the</strong> seed bank, c<strong>on</strong>trol of broom will require fire <strong>on</strong> <strong>the</strong> Mountain.Odi<strong>on</strong> and Haubensak (in press), studied resp<strong>on</strong>se of French broom seed banks to burning. In mixedannual/native grassland <strong>on</strong> <strong>the</strong> watershed, 1-2 in tall, 5-10 year old broom stands had 500-4300 seeds/m 2 .Burning cut stands with <strong>the</strong> additi<strong>on</strong> of slash fuel significantly increased germinati<strong>on</strong>, and following a sec<strong>on</strong>dburn 1 year later, emergence was reduced to low levels. In c<strong>on</strong>trast, 2-3 in tall, 15-25 year old stands had4,300-14,000 seeds/m 2 , with a sizable porti<strong>on</strong> too deeply buried to be killed or induced to germinate using firetreatments.Grassland soils invaded by broom also had significantly more available nitrogen than soils in uninvadedplots. After burning, broom invaded areas remained enriched. Soil nitrogen enrichment is a c<strong>on</strong>cern because ithas been documented in many cases, going back to <strong>the</strong> work of Lawes and Gilbert in 1880 (see Vitousek et al.1997), that this may shift dominance to nitrogen demanding plants. Thus, French broom may alter sites to bemore favorable to fast growing, weedy plants, and it is uncertain how to ameliorate this.Broom C<strong>on</strong>trol StrategyThe most important c<strong>on</strong>clusi<strong>on</strong> from this research is that as broom stands age (Fig. 1), seed accumulati<strong>on</strong> atgreater soil depths will cause a transiti<strong>on</strong> from an infestati<strong>on</strong> that may be possible to c<strong>on</strong>trol with fuel additi<strong>on</strong>,repeat burning and follow up treatments, to <strong>on</strong>e that will require chr<strong>on</strong>ic treatment indefinitely to eliminateemerging plants. Un<strong>for</strong>tunately, most broom infestati<strong>on</strong>s <strong>on</strong> <strong>the</strong> watershed have already underg<strong>on</strong>e thistransiti<strong>on</strong>. There<strong>for</strong>e, we developed a two-pr<strong>on</strong>ged management strategy, <strong>on</strong>e <strong>for</strong> dealing with a resilient landailment and ano<strong>the</strong>r <strong>for</strong> preventing infestati<strong>on</strong>s from becoming a resilient ailment.Fig. 1. Changes in French broom seed bank with time.<str<strong>on</strong>g>Fire</str<strong>on</strong>g> is needed to c<strong>on</strong>trol both young and old stands because it depletes <strong>the</strong> seed bank. It also c<strong>on</strong>trolsresprouting if repeated every 1-4 years, so that regenerating broom does not reach reproductive age. <str<strong>on</strong>g>Fire</str<strong>on</strong>g> costsrelatively little, provides additi<strong>on</strong>al ecological benefits, and does not raise toxicological c<strong>on</strong>cerns. MMWD hasnot c<strong>on</strong>sidered methods of pois<strong>on</strong>ing seed, or <strong>the</strong> soil that seedlings emerge through, because <strong>the</strong>se have broadspectrum biocidal impacts that are unacceptable <strong>on</strong> Watershed lands. The same would apply in most wildlandsettings. O<strong>the</strong>r methods of eliminating existing broom stands (Table 2) have little effect <strong>on</strong> <strong>the</strong> seed bank.Herbicides are listed am<strong>on</strong>g broom killing tools in Table 2 because <strong>the</strong>y will be an opti<strong>on</strong> <strong>for</strong> many landmanagers. MMWD policy prohibits using <strong>the</strong>se chemicals <strong>on</strong> lands draining into reservoirs, and, due to publicsentiment, avoids any broadcast applicati<strong>on</strong> <strong>on</strong> o<strong>the</strong>r lands it manages.With prescribed fire, <strong>the</strong>re is <strong>the</strong> risk of escape and of causing unintended mortality of n<strong>on</strong>-sproutingc<strong>on</strong>ifers (Swezy and Agee 1991). There are also negative effects from repeat and out-of seas<strong>on</strong> burning inPage 2
<strong>Cal</strong>i<strong>for</strong>nia Exotic Pest Plant Council1997 Symposium Proceedingschaparral (Zedler et al. 1983, Parker 1987). Because of <strong>the</strong>se c<strong>on</strong>cerns, we have made chaparral infested areasa lower priority than mixed evergreen <strong>for</strong>est and grasslands, where fire as frequent as needed <strong>for</strong> broom c<strong>on</strong>trolappears to have no unwanted side-effects.Preventing Fur<strong>the</strong>r SpreadEliminating broom infestati<strong>on</strong>s be<strong>for</strong>e <strong>the</strong>y become resilient will be critical to l<strong>on</strong>g-term c<strong>on</strong>trol. Parametersin <strong>the</strong> model shown in Figure 1 need to be refined to predict at what point <strong>the</strong> critical transiti<strong>on</strong> in <strong>the</strong> seed bankoccurs and to identify sites that can be restored now, but that will become inveterate infestati<strong>on</strong>s if treatment isdelayed. The repeat bum method with initial pulling or cutting, and fuel additi<strong>on</strong> will be effective <strong>for</strong> sufficientlyyoung infestati<strong>on</strong>s.Road grading, trail work, and o<strong>the</strong>r maintenance activities may disperse seed. Limiting or stopping use ofroads and trails in infested areas during muddy c<strong>on</strong>diti<strong>on</strong>s would be a beneficial preventi<strong>on</strong> strategy, but may beimpossible <strong>for</strong> MMWD and o<strong>the</strong>r public land managers in central and nor<strong>the</strong>rn <strong>Cal</strong>i<strong>for</strong>nia because of <strong>the</strong> public'srecreati<strong>on</strong>al demands.Table 2. Properties of Broom Tools Used by Marin Municipal Water DistrictCost (approx.Tool Advantages Disadvantagesretail)hand pulling Good <strong>for</strong> small plants in moist Limited seas<strong>on</strong> and size. Strains labor cost <strong>on</strong>lyc<strong>on</strong>diti<strong>on</strong>sback.Pulaski<str<strong>on</strong>g>Fire</str<strong>on</strong>g>fighting tool good <strong>for</strong> grubbing Disturbs soil. Not appropriate in $25-$45out gnarly root masses.most cases.Root Jack Efficient hand puller. Light weightand portable.Can't attach to really large stemsWooden handle breaks <strong>on</strong> tough$90Weed WrenchBrushcutter(weed whip)chain sawpropane torchw/flame spreaderflail mowertractor-mountedbrush cutterexcavatormountedprescribed fireHeavy duty, powerful hand puller.Variety of sizes.Good <strong>for</strong> cutting shrubs close to <strong>the</strong>ground. Useful <strong>for</strong> small stems andseedlings.Good <strong>for</strong> cutting <strong>on</strong> steeper slopesand <strong>for</strong> larger stems. Cuts quickly.N<strong>on</strong>-toxic technique <strong>for</strong> roadsideseedlings.Very productive <strong>for</strong> mowingroadside plants.Can travel off of roads. Low groundpressure. Excellent pre-treatment<strong>for</strong> prescribed burning.Only method that reduces seed bank.Can benefit natives.plants.Larger sizes are heavy to carry.Doesn't attach to stems as easily asRoot Jack but holds tighter.Difficult to use <strong>on</strong> steep ground.Cuts slower than a chain saw.Dangerous, need safety gear.Not good <strong>for</strong> smaller stems. Backstrain to cut low. Dangerous, needsafety gear.<str<strong>on</strong>g>Fire</str<strong>on</strong>g> hazard, limited to wet seas<strong>on</strong>.Not very portable off of road.Sprouts require retreatment at2-year interval. Can't go off ofroads.Limited to slopes less than 35%slope. Can't maneuver betweentrees. Must treat stump sprouts.May require pre-treatment.Escapes are a possibility. Notappropriate in all locati<strong>on</strong>s.$50-$150commercial grade$500-$600$250-$500$150$50,000$100-$150,000$50-$400/acreHerbicide Efficient, easy. See DiTomaso* Toxicology c<strong>on</strong>cerns. See variableDiTomaso*bio-c<strong>on</strong>trol Benign Not effective <strong>for</strong> broom. research isexpensive*Proceedings. 1997. <strong>Cal</strong>i<strong>for</strong>nia Exotic Pest Plant Council Symposium, Vol. III.Page 3