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Combining active restoration and targeted grazing to establish native plants and reduce fuel loads in invaded ecosystems

Authors:

Abstract

Many drylands have been converted from perennial‐dominated ecosystems to invaded, annual‐dominated, fire‐prone systems. Innovative approaches are needed to disrupt fire‐invasion feedbacks. Targeted grazing can reduce invasive plant abundance and associated flammable fuels, and fuelbreaks can limit fire spread. Restored strips of native plants (native greenstrips) can function as fuelbreaks while also providing forage and habitat benefits. However, methods for establishing native greenstrips in invaded drylands are poorly developed. Moreover, if fuels reduction and greenstrip establishment are to proceed simultaneously, it is critical to understand how targeted grazing interacts with plant establishment. We determined how targeted grazing treatments interacted with seed rate, spatial planting arrangement (mixtures vs. monoculture strips), seed coating technology, and species identity (five native grasses) to affect standing biomass and seeded plant density in experimental greenstrips. We monitored for two growing seasons to document effects during the seedling establishment phase. Across planting treatments, ungrazed paddocks had the highest second‐year seeded plant densities and the highest standing biomass. Paddocks grazed in fall of the second growing season had fewer seedlings than paddocks grazed in spring, five months later. High seed rates minimized negative effects of grazing on plant establishment. Among seeded species, Elymus trachycaulus and Poa secunda had the highest second‐year densities, but achieved this via different pathways. Elymus trachycaulus produced the most first‐year seedlings, but declined in response to grazing, whereas P. secunda had moderate first‐year establishment but high survival across grazing treatments. We identified clear tradeoffs between reducing fuel loads and establishing native plants in invaded sagebrush steppe; similar tradeoffs may exist in other invaded drylands. In our system, tradeoffs were minimized by boosting seed rates, using grazing‐tolerant species, and delaying grazing. In invaded ecosystems, combining targeted grazing with high‐input restoration may create opportunities to limit wildfire risk while also shifting vegetation toward more desirable species.
Ecology and Evolution. 2018;1–14.    
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www.ecolevol.org
Received:30April2018 
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  Revised:1 2September2018 
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  Accepted:17Septemb er2018
DOI: 10.1002/ece 3.4 642
ORIGINAL RESEARCH
Combining active restoration and targeted grazing to establish
native plants and reduce fuel loads in invaded ecosystems
Lauren M. Porensky1| Barry L. Perryman2| Matthew A. Williamson3|
Matthew D. Madsen4| Elizabeth A. Leger5
Thisisanop enaccessarti cleundertheter msoftheCreativeCommonsAttributionL icense,whichpe rmitsuse,dis tribu tionandreprod uctioninanymed ium,
provide dtheoriginalwor kisproperlycited.
©2018TheAut hors.Ecology a nd EvolutionpublishedbyJoh nWiley&SonsLtd.
1RangelandResourcesandSystemsResearch
Unit,US DAAgricultur alResearchSer vice,
FortCollins,Colorado
2DeparmentofAgriculture,Nutritio nand
Veterinar yScie nces,UniversityofNevada,
Reno,Nevada
3Depar tmentofEnvironmentalScience
andPolic y,UniversityofCalifornia,Davis,
California
4Depar tmentofPlantandWildlife
Science s,BrighamYoungUni versit y,Provo,
Utah
5Depar tmentofNaturalResour cesand
EnvironmentalS cience ,Univer sityof
Nevada,Reno,Nev ada
Correspondence
LaurenM.Poren sky,RangelandRe source s
andSystemsResearchUnit ,USDA
AgriculturalResearchSer vice,Fo rtCol lins,
CO.
Email:lauren.porensky@ars.usda.gov
Funding information
WesternIntegratedPestManagement
Center,Universit yofCalifornia,Davis,
Grant /AwardNumber:2013-34103-21325
Abstract
Many dryl ands have been conver ted from perennial-d ominated ecosyste ms to in-
vaded,annual-dominated,fire-pronesystems.Innovativeapproachesareneededto
disrupt fir e-invasion feedbacks. Targeted graz ing can reduce invasive plant a bun-
danceandassociatedflammablefuels,andfuelbreakscanlimitfirespread.Restored
stripsofnativeplants(nativegreenstrips)canfunctionasfuelbreakswhilealsopro-
vidingforageandhabitatbenefits.However,methodsforestablishingnativegreen-
strips in inva ded drylan ds are poorly develop ed. Moreover, if fuels reduc tion and
greenstripestablishment aretoproceedsimultaneously,itiscriticalto understand
howtargeted grazing interacts with plantestablishment. We determined howtar-
geted grazing treatment s interacted with seed rate, spatial planting arrangement
(mixturesvs.monoculturestrips),seedcoatingtechnology,andspeciesidentity(five
nativegrasses)toaffectstandingbiomassandseededplantdensityinexperimental
greenstrips.Wemonitoredfortwogrowingseasonstodocumenteffectsduringthe
seedling establishment phase. Across planting treatments, ungrazed paddocks had
the highest second-year seeded plant densities and the highest standing biomass.
Paddocksgrazedinfallofthesecondgrowingseasonhadfewerseedlingsthanpad-
docksgrazedinspring,fivemonthslater.Highseedratesminimizednegativeeffects
ofgrazing on plantestablishment.Amongseeded species, Elymus trachycaulusand
Poa secunda had the highest second-year densities, but achieved this via different
pathways.Elymus trachycaulusproducedt hemos tfi rst-yearsee dling s,b utdec linedin
response to grazing,whereasP. secu n da hadmoderatefirst-yearestablishmentbut
high survival across grazingtreatments. We identified clear tradeoffsbetween re-
ducingfuelloadsandestablishingnativeplantsininvadedsagebrushsteppe;similar
tradeoffs may existinother invaded drylands. Inoursystem,tradeoffs weremini-
mizedbyboostingseedrates,usinggrazing-tolerantspecies,anddelayinggrazing.In
invaded ecosystems, combining targeted grazing with high-input restoration may
createopportunitiestolimitwildfireriskwhilealsoshiftingvegetationtowardmore
desirablespecies.
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   PORENSKY Et a l.
1 | INTRODUCTION
Firesize,frequencyandseverityareincreasingduetoclimatechange
andlandusechange,andshiftingfireregimesarealteringecosystem
function and ecosystem service provisioning globally (Abatzoglou,
Kolden, W illiams, Lut z, & Smith, 2017; Denniso n, Brewer, Arnold,
& Morit z, 2014;M oritz et al. , 2014).W ith a warming cl imate, the
most ef fective st rategies to ma nage increase d fire acti vity will b e
thoseresultinginself-sustainingplantcommunitiesabletoresistor
recover from firewithouttheneed for continuing management in-
puts (Su ding et al., 2015) . Neverth eless, many c urrent appr oaches
towildlandfiremitigationrelyontherepeateduseofbrushcontrol,
herbicide-ormechanicallygeneratedfuelbreaks(“brownstrips”),or
ongoing ac tive fire suppre ssion (Wildla nd Fire Executive C ouncil,
2014). Strategies that rely on restoring historic vegetation struc-
ture,suchasrecentef fort sinforestedsystems(Fule,Covington, &
Moore, 1997), can provide lasting benefits by increasing long-term
resilience and resistance to future fire (Hanberry, Noss, Safford,
Allison,&Dey,2015).
In many dryland shrublands, wildfires have been historically
smallan dinfre quentb ec aus efiresrarel ysprea dthroughs parse ,dis-
continuous vegetation (Klinger & Brooks,2017). However,historic
plant community compositionand structurein many of these eco-
systems h ave been dras tically a ltered by the i ntroduc tion of inva-
siveannual grasses (e.g.,Bromus tectorum L., Bromus rubens L., and
Schismusspp.P.Beauv.)that increasefuelloadsandfuelcontinuity
asbiomass accumulatesbetweenshrubsandperennial grasses, ul-
timatelyincreasingthelikelihoodof fireignition andspread(Balch,
Bradley, D’Antonio, & Gómez-Dans, 2013; Brooks et al., 2004;
Davies & Nafu s, 2013). Feedbac ks betwee n fire and inva sive spe-
ciescancausewidespreadecosystemconversions,forexamplefrom
shrublands to grasslands dominated by nonnative annuals (Alba,
Skalova , McGregor, D’Antonio, & P ysek, 2015; Balch et a l., 2013;
D’Antonio&Vitousek,1992).Asaresult,effor tstorestoreinvaded
shrublands are increasingly focused on reducing fuelloadsor fuel
connectivityandrestoring fire-resistantvegetationstructure(Gray
& Dickson, 2015, 2016; Pellant, 1989). To provide long-term fire
resistance,restorationshouldincludereplacingfire-proneinvasive
species with less flammablespecies, but thishas proved elusive in
areaswithhighfirefrequencyandintensecompetitionfrominvasive
species(Duniway,Palmquist,&Miller,2015;Eiswerth&Shonkwiler,
2006;P yke,Wir th,&Beyers,2013).
Ininvadeddr ylands,developingmanagementstrategiesthatcan
simultaneously increase the establishment of fire-resistant plant
species and decrease the risk offirespread wouldbe an impor tant
steptowardrestoringfireregimescharacterizedbysmall,infrequent
wildfires.Manydrylandecosystemsarecurrentlyusedforlivestock
grazing,makingtargetedgrazinganattractiveoptionforvegetation
management. Targeted grazingisdesignedtoachieve specific veg-
etation m anagement goa ls, such as red uced fuel loa ds or reduced
coverofinvasiveplants,viaspecifiedtiming,duration,andintensity
of use (Frost & L aunchbaug h, 2003). Targeted g razing can dis rupt
invasion-firefeedbackcyclesbyreducingfuelloadsandconnectivity
(Davies,Bates,Boyd,&Svejcar,2016;Davies,Bates,Svejcar,&Boyd,
2010;Davies,Boyd,Bates,&Hulet,2016;Davies,Gearhart,Boyd,&
Bates,2017;Davies,Svejcar,&Bates,2009;Diamond,Call,&Devoe,
2009; Schmelzer et al., 2014).Byreducinglitter thatfacilitatesan-
nual grass dominance (Beckstead & Augspurger, 2004; Jones,
Chambers, Board, Johnson, & Blank, 2015), targeted fall grazing
canalsonegativelyimpactannualgrassperformanceinsubsequent
years with minimal negative ef fect s on perennial bunchgrasses
(Schmelzer et al.,2014;Trowbridge et al., 2013). Fur ther, targeted
spring grazing canreduce annual grassseed production(Diamond,
Call,&Devoe,2012).Viathesemechanisms,targetedgrazingshould
reduce competition between invasive annuals and restored, fire-
resist ant plants . However, it is unclear w hether th e net effec ts of
targetedgrazingpracticesonplantedseedlings arepositiveorneg-
ative (Figure 1). Defoliation and uprootingare likely to reduce the
survival and growth of individual seedlings, but targeted grazing
treatments may indirectly assist planted seedlings by reducing lit-
ter,biomass, anddensities of competitive invasive annuals, andby
reducingwildfirerisk(Figure1).Targetedgrazing can reducenative
grassseedbanks(Diamondetal.,2012;Schmelzer,2009),buttoour
knowledge,nostudieshaveinvestigatedimpactsoftargetedgrazing
onnativeseedlingestablishmentinwesternUnitedStatesdrylands.
Like targeted grazing, fuelbreaks have been used asameans
ofreducing fuelloads andfuel connectivity,particularlyinareas
where roadsprovide a potential ignition source or to protect in-
frastructureinwildland-urbaninter faces (Pellant,1989).Without
continuedmaintenance,mechanicallyorchemicallycreatedfuel-
breaks(“brownstrips”)canexacerbateinvasivespecieschallenges
(Merriam, Keeley, & Beyers, 2006).Greenstrips,which are linear
planting s designed to r educe fire size or f requenc y and prevent
firespreadintouninvadedorrestoredareas,areanalternativeap-
proachaimedatcreatingpatchesofself-sustaining,fire-resistant
vegetation(Pellant,1989).Toresistwildfire,greenstripsmustei-
therinclude vegetationwithlowbiomassandlargegapsorvege-
tationthatmaintainshighmoisturecontentduringthefireseason
(Monaco, Waldron, Newhall, &Horton, 20 03; Robbins, Staub, &
Bushman,2016).GreenstripsinthewesternUShaveoftenrelied
onnonnativeplantspecies(Harrisonetal.,2002),butgreenstrips
compose d of native plants h ave the potential to pr ovide added
benefi ts such as native bio diversity and wi ldlife habitat va riety
(Hulvey et al., 2017) whileavoiding the unintended spread of in-
troduce d species (Gr ay & Muir,2 013). Further, relative to m ore
diffuse native plant restoration approaches, native greenstrips
KEY WORDS
Bromus tectorum,brownstrip,foragekochia,greenstrip,precisionrestoration,surfactant
    
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 3
PORENS KY Et a l.
may lead to gre ater return-on-inve stment becaus e a greenstrip
approachallowspractitionerstoconcentrateeffortandresources
intosmall,spatiallystrategiclocations(Hulveyetal.,2017).
It remains u nclear how to bes t produce native gre enstrips, or
how to combinegre enstrips with targeted grazing to disrupt fire-
invasion fe edbacks. Es tablishin g native plants f rom seed in highl y
invadedsettingsremainschallenging(Eiswerth&Shonk wiler,2006).
Existing work on restoration in drylands suggests that seedling
estab lishment is a crit ical bottl eneck in these e cosystems (J ames,
Svejcar,&Rinella,2011),withsur vivorshipincreasingsubstantially
after thefirstor second growingseason (Leger & Goergen, 2017).
Ourwork explored the separate and combined efficacyoffive ap-
proachesthat couldpotentially be utilized to alter competitivedy-
namics and increase seedling establishment in dryland ,f ire-prone
restoration settings: using seed coatings to increase water avail-
ability(Madsen,Kostka,Inouye,&Zvirzdin,2012),choosingspecies
thatcancompeteattheseedlingstagewithinvasiveannuals(Rowe
& Leger, 2011), bolsteri ng seed rates (Ma zzola et al., 2010), usin g
spatial separation to reduce competition among planted species
(Porensk y,Vaughn, & Young, 2012),and usingtargeted spring and
fallgrazingtoreduceinvasiveplantcompetitionandassociatedwild-
firerisk(Daviesetal.,2017;Schmelzeretal.,2014).
Weimplemented a 164-ha experimentat a highly invaded site
inthe GreatBasin regionofthe westernUS. In this region, almost
1/3ofthelandarea(210,000km2) ishighlyinvadedbyannualspe-
ciesthatburnwithgreaterfrequencythanvegetation inuninvaded
areas(Bradleyetal.,2018).TheinvasionofB. tectoruminthisregion
has cause d a widesprea d loss of wildlife ha bitat, lives tock forage,
soil health, plant genetic diversity, and other ecosystem services
(DiTomaso, 2000; Eiswerth, Darden, Johnson, Agapoff, & Harris,
2005; Ma ck, 1981).Bromus tectorum increase swildf iref requency
and extent (Balch et al., 2013; Davies & Nafus, 2013), making this
anexcellentsystemforinvestigatingtheefficacyoftargetedgrazing
andnativegreenstripplantingsastoolsfordisruptingwildfire-inva-
sionfeedbacks.Wehypothesizedthat:
1. Targeted fall and spring grazing during the second growing
season wou ld reduce invasi ve species biom ass, litter cove r and
invasive plant densities via direct consumption of plants and
seeds and trampling of litter.
2. Targetedgrazingduringthesecondgrowingseasonwouldreduce
densitiesofseededspeciesinexperimentalgreenstrips,and,be-
cause plants are actively growing, spring grazing would have
strongernegativeeffectsthanfallgrazing.
3. Higher seed rates, seed coatings, use of competitive native
grasses, and spatially segregated planting arrangements would
enhance seedling establishment,mitigating any negative effects
oftargetedgrazing.
2 | METHODS
2.1 | Study site
Our site was i n norther n Nevada at the T S Ranch (Elko Lan d and
Livesto ck Company; 40. 843–40.895N, 116.50 9116.554W). Th e
siteisasoutheast-facing, gentlysloping alluvial fanonloamysoils,
andtheclimateistypicalofacolddesert(250mmannualprecipita-
tion,averagedailytemperatureis−3°CinJanuaryand22°CinJuly,
PRISMClimateGroup,).Precipitationwasaverageduringtheestab-
lishmentyear(248mmfrom10/1/2014–9/30/2015)andaboveaver-
ageduringthesecondseason(323mmfrom10/1/2015–9/30/2016;
Suppor ting InformationTable S1).Vegetation wasdominatedbyB.
tectorumandnonnativeannualforbsincludingSisymbrium altissimum
L.,Lepidium perfoliatum L., Salsola tragus L .,Ceratocephala testiculata
(Crantz)Roth,andChorispora tenella (Pall.)DC.Afewnativespecies
FIGURE 1 Hypothesizeddirectand
indirecteffectsofgrazingonnative
plantest ablishmentingreenstrips(red
andbluearrows),andhypothesized
effectsofestablishedgreenstripson
invasion,wildfireandseason-longforage
availability(greenarrows).Second-year
resultsprovideevidencefornegative
directeffectsofcattlegrazingonboth
seedlingestablishmentandinvasive
plantbiomass,butnoevidenceforcattle
grazingef fectsonlittercoverorinvasive
plantdensity
Calegrazing
Nave plant
establishment
in greenstrips
Invasive plant
biomass and
density
Lier cover
+
-
-
-
-
Wildfire
+
+
-
-
Indirect+
Established
greenstripsSuppress
Enhance
4 
|
   PORENSKY Et a l.
werepresent includingPoa secunda J.Presl, Elymus elymoides (R af.)
Swezey,Vulpia microstachys (Nutt.)Munro,Microsteris gracilis (Hook.)
Greene, Crepis oc cidentalis Nutt .,Amsinckia tessellata A. Gr a y, Lappula
occidentalis (S.Watson)Greene,andMentzelia albicaulis (Hook.)Torr.
& A. Gray. Based on vegetation composition of surrounding un-
burnedareaswithsimilarlandposition,wehypothesizethatthissite
hadvegetation typical of lowland sagebrush steppe (dominatedby
Artemisia tridentata Nutt.ssp. wyomingensis Beetle &Young,peren-
nialbunchgrasses,andannualforbs)priortoinvasion.
2.2 | Experimental design
The expe rimental desig n was hierarchica l with three levels (sp lit-
splitplot,Smith,Pullan,&Sh iel ,1996).Atth ebroad estscale,arand-
omizedcompleteblockdesignwasemployedforgrazingtreatments.
Nine18.21hapaddockswerearrangedintothreeblocks(Figure2a).
On ep add ock perbl ock wasra ndo mly as sig nedto ea c ho ft hre eg r az-
ing treatments: fall, spring, or no grazing. Blocks werearranged to
capturepotentialvariationassociatedwithtopographicandagricul-
turalfeatures(Figure2a).
Withineachpaddock(middlelevelofthehierarchicaldesign),we
establishedtwelve0.12haexperimentalgreenstripplots(20×60m)
separat ed by ≥50m. Eight of th ese plots wer e randomly a ssigned
tofour native grass restoration treatments, with two replicates of
eachtreatmentperpaddock.Treatmentsincluded all combinations
oftwospatialarrangementtreatment sandtwoseedratetreatments
(Figure2b).Spatialarrangementtreatments included“monoculture
strip” plots, in whichspecieswereseededseparately into adjacent
4-mwide strips, and “mixture” plots, in whichthesame amount of
seed was mixedacross all species beforeplanting.Seed rate treat-
mentsincluded1×or2×seedrates,where1×ratesfollowedrange-
landrestorationguidelinesforeachspeciesbasedonatotalpurelive
seed(PLS)rateof646seeds/m2.
Theseed mix included five grassspecies witha diversity of life
historystrategies,whichwereselectedfromapoolofspeciesnative
to the regio n. Species in cluded two gr azing-tolerant , early-seaso n
perennial bunchgrasses (E. elymoides, squirreltail, and P. s ecu n da,
Sandberg bluegrass) and one annual grass (Vulpia microstachys
(Nutt .) Munro, small fesc ue). We expected the se species to com-
petewellwithB. tectorumduetosimilarphenology(Leger,Goergen,
& Forbis de Queiroz, 2014). Two taller, deeper-rooted perennial
grassesthat typically staygreen into the fire season were also in-
cluded:oner hizo ma to ussp ec ie s( Elymus trachycaulus(Link )G ou ldex
Shinners,slender wheatgrass)and onebunchgrass(Poa fendleriana
(Steud.) Vasey,muttongrass).Seed ratesforthe1×treatment were
asfollows:E. elymoides3.05PLSkg/ha;E. trachycaulus4.34PLSkg/
ha;P. fendleriana0.65PL Skg/ha;P. s ecu nda 0.56PL Skg/ha; andV.
microstachys0.61PLSkg/ha.
Atthefinestscaleoftheexperimentaldesign(split-splitplot),each
experimentalgreenstripplotincludedthree20×20msubplots,one
ofwhichwasrandomlyselectedforacoatedseedtreatment.Seeds
ofeachspecieswerecoatedwithanonionicalkylterminatedblock
copolymersurfactantcoatingbasedonC1–C4alkylethersofmethyl
oxirane–oxirane copolymers (Aquatrols Corporation of America,
Paulsboro,NJ). This sur factant has beenused to increase the wet-
tabilityofwater-repellentsoils(Ferneliusetal.,2017;Kostka,200 0)
FIGURE 2 Theexperimenthadahierarchicaldesignwiththree
levels.(a)Blocksandpaddock-scaletreatments.Eachofthree
blockscontainedthree18. 21hapaddocksrandomlyassigned
todifferentgrazingtreatments.Eachpaddockcontainedtwelve
0.12haplantedplotsandtwelveunseededcontrolplots.Unseeded
controlplotswererandomlyinterspersedamongplantedplots
(>15mand<50mfromanyplantedplot).(b)Plot-andsubplot-scale
treatments.Thetwelveplotswithineachpaddockwererandomly
assignedtosixdifferenttreatments.Plotsplantedwithgrasses
alsoincludedthree20×20msubplots,oneofwhichwasrandomly
assignedtothecoatedseedtreatment.Inmonoculturetreatments,
colorsrepresentdifferentspecies.Plantcoverandseededspecies
densitiesweresampledinbothredandblackquadrats;nonseeded
speciesdensitieswereonlysampledinredquadrats
(b)
(A)
Herbicide only
Kochia
Mixedspaal arrangement,
Lowseed rate
Monoculture spaal arrangement,
Lowseed rate
sampling quadrats
Mixedspaal arrangement,
High seed rate
Monoculture spaal arrangement,
High seed rate
Uncoated seed
Coated seed
60 m
20 m
Uncoated seed
Coated seed
Uncoated seedCoated seed
Uncoated seed
Coated seed
    
|
 5
PORENS KY Et a l.
butal soimprove splantd ro ughttol er an ceinwet tablesoilsbyr ed uc-
ingthetimeittakesfor aroottorehydrateandbydecreasingplant
transpirationrates(Ahmedetal.,2018).Increaseddroughttolerance
providedby the seed coatingcouldproducemore vigorous plants
withgreater seedlingsurvival.Seedratesweredeterminedpriorto
coating. In each paddock, we also included two 0.12ha nonnative
greenstripplotsseededwithforagekochia(Bassia prostrata (L.) A. J.
Scott , 6.73 PLS kg/h a), and two 0.12ha brown strip plot s sprayed
withthetargetedherbicide imazapic.Bothofthese techniquesare
commonl y used to create fir ebreaks on B. tector um-inva ded sites,
andtheirinclusionallowedfordirectcomparisonswithnativegrass
greenstriptreatments.
All plot s were initially spr ayed with glyphos ate in April 2014,
priortoseeding(840g/ha).Herbicideplotswereresprayedinspring
2015and2016 with imazapic(420g/ha). Plotsassigned toseeding
treatments were notresprayed and wereseededwith a rangeland
drillinOctoberandNovember2014.Grazingtreatmentswereiniti-
atedinFall2015,providingafullgrowingseasonofdeferment.Fall-
grazedpaddocksweregrazedby25cows(25animalunits[AUs])for
7–9dayseachbetween 15Oc tober and9November2015.Spring-
grazedpaddocksweregrazedby29yearlings(22AUs)for9–11days
eachbetween 5Apriland4May2016.Grazingperiodsandgrazing
animalsweredeterminedbasedonavailabilityoflivestock,withan-
imalssplitbetweenpaddocks forthetimeavailableandleavingnot
lessthan112kg/haofst andingcrop.
2.3 | Data collection
Toa ddress Hypot hesis 1, we quant ified stan ding biomass in J une
2015, prior to g razing treatm ents, in each p addock by har vesting
aboveground biomass rooted inside five 1-m2 plots per paddock
(four unseeded controls and one randomly selected native grass
plot). Unse eded control pl ots were located r andomly with in each
paddoc k but outside of p lanted plots (>15m and <50m from any
planted plot). In November 2015 and May 2016, we applied the
same methodat16locationsperpaddock(four unseeded controls
andall12treatmentplots),andseparatedclippedbiomassintofour
functionalgroups:B. tectorum, forbs, native grasses, andseedlings
of planted sp ecies. Clip l ocations were s hifted by 3–5m betwe en
samplingperiodstoavoidresamplingpreviouslyclippedareas.
ToaddressHypotheses 2and 3, seedlingemergenceand aerial
cover were sam pled in May 2015 and M ay-J une 2016 at multiple
locationswithin each plot (see Figure2bfor sampling locations). In
2016,wealso sampled emergence andcover at 12 unseeded con-
trol plots per paddock. Unseeded controls were thus monitored
withineachgrazingtreatment.In2015,wecountedseedlingswithin
25×50cmquadratateachsamplinglocation.In2016,wesampled
atthesame loc ations butused a50x50 cm quadrat to ensurethat
seededspecieswereencounteredduringdensitycounts,duetoden-
sityreductionsbetween2015and2016.Atthesamesamplingl oca-
tions, in each year,we visuallyestimatedpercent plantfoliar cover
(plant materialthatwould interceptaraindrop) by speciesforboth
seed ed an dn onsee dedspec ie si na1-m2quadrat.Forportionsofthe
quadrat withoutplantcover,weestimated coveroflitter(det ached
plant tiss ue) and bare groun d. Integer increm ents from 0%–100%
wereusedforvisualcoverestimates.Becauseofsmallseedlingsizes,
itwasdifficulttoconfidentlydistinguishamongsomeplantedgrass
species(e.g,Elymus elymoides andE. trachycaulus)in mixture plots,
soseededspeciesdensitiesandaerialcoverofseededspecieswere
recordedinaggregatefortheseplots.Monocultureplotswereused
toevaluatedif ferencesinestablish mentsu cce ssamongseededspe-
cies.Att wosamplingstationsperplot(Figure2b),wealsorecorded
densitiesofnonseededspeciesina25×25cmquadrat.
2.4 | Data analysis
ToaddressHypothesis1,dataonabovegroundbiomass,littercover,
andinvasivespeciesdensityandcoverwereanalyzedforeachyear
usinglinearmixedmodels.Randomeffectsincludedblock,paddock
nested within block, and (for coverand density analyses only)plot
nested within paddock and block. Fixed effects included grazing
treatments, plottypes(controlandgrassforbiomassinJune2015;
control, grass,herbicideandkochiaforallotheranalyses),andtheir
interaction.ThoughplotshadnotyetbeengrazedinJune2015,we
includedtheplannedgrazing treatment in thesemodels totest for
pretreatmentdifferences.TheseanalyseswereconductedwithJMP
(JMP®,Version 12. SAS Institute Inc.,Cary,NC, 1989–2007).Data
were transformedand variance-weightedwhen necessar y to meet
modelassumptions.
To address Hypot heses 2 and 3, see dling data were ana lyzed
usinggeneralizedlinearmixedmodels with anegativebinomialdis-
tribut ion due to zero-inflate d count data. This d istribution f it the
data signi ficantly bet ter than severa l other potential d istribution s
(e.g.,Gaussian,Poisson,Gamma).Weanalyzedeachyearseparately
tobetterunderstandthefactorsinfluencingplantsuccessatdiffer-
entdemographic stages. Foreach year,weran threemodelsusing
seedlin gs of planted spec ies per m2 as the re sponse variab le. For
all model s, random ef fects i ncluded blo ck, paddo ck nested wit hin
block, andplotnested withinpaddockandblocktoaccountfor the
experiment’shierarchicaldesign.Twoquadratslocated4mapartin
thesameplothadextremelyhighnumbersofresident(nonseeded)
V. microstachysandwerethereforeexcludedfromallanalyses.
Thefirstmodel(“grazing×establishmentmodel”) determined if
grazing treatments affected seedlingdensities and if plots planted
withnativegrasses haddifferentseedling densitiesthanforageko-
chiaplot s,herbicideplots,orunplantedcontrols.Foryearonedata,
collectedpriorto initiationofgrazingtreatments, theonlyfixed ef-
fect in th e model was pl ot type (g rass or forage ko chia; seedlin gs
were not censu sed in control plot s in year one). For secon d-year
data, fixedeffects includedplot type(grass,forage kochia,orcon-
trol),grazingtreatment,and theirinteraction.Herbicide plotswere
excluded f rom analysis of se cond-year data be cause no seedl ings
wereobserved.
Thesecondmodel(“plantingstrategiesmodel”)assessedtheef-
fectsofmultipleplantingmethodsonseedlingdensities,usingonly
data from plots seeded with nativegrasses. Fixed ef fect sincluded
6 
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   PORENSKY Et a l.
seedrate,spatial arrangement,seedcoating, grazingtreatment (for
second-yea r data), and all inter actions amo ng these fac tors. Seed
coating sub plot was adde d as an addition al random ef fect neste d
withinplot,paddockandblock.
Thethirdmodel(“grassspeciesmodel”)assessedhowspecies-
level dif ferences af fected see dling densit ies, using onl y data from
monoculture grassplots. Fixed effects included species,seed rate,
grazing treatment(forsecond-year data),seedcoating,andtwo-or
three-way interactions. Seed coating subplot was again included
as a random effect. Seedling analyses were performed with the
lme4 statistical package (Bates, Maechler,Bolker,&Walker,2015)
in R (version 3 .3.1). Denomin ator degrees of freed om were deter-
minedconservativelybasedonthehierarchicalexperimentaldesign
(Pinheiro&Bates,2000)andusedtocalculatep-values.Resultswere
consideredsignificantatp<0.05 and are reported asmean±stan-
darderror(SE).
3 | RESULTS
3.1 | Grazing reduced standing biomass, but not
litter or invasive plant densities
Standingbiomassdidnotdifferamonggrazingtreatmentsorbe-
tweenunseededcontrolsandseededplotsbeforegrazingtreat-
ments were implemented (June 2015 biomass p-values>0.4).
Fallgrazing reduced standing biomass by 30%–4 0% (Figure3a,
F2,8=7.37,p=0.02).Followingfallgrazing,acrossgrazingtreat-
ments, plots se eded with forage kochia and grasses had 91%
and 30% m ore standing b iomass than uns eeded control p lots,
respectively, and unseeded control plots had 4. 5 times more
biomassthanherbicideplots(SupportingInformationTableS2;
F3,120=30 .5, p<0.00 01). Planted seedli ngs were too small to
contributetobiomass,soincreasedstandingbiomassinseeded
plotsrelative tounseeded controlswasaresultofinvasivespe-
ciesresponsestothemechanicaldisturbanceofthedrill.
The spring grazing treatment reduced standing biomass
by 50% relative to ungrazed plots in May 2016 (Figure 3a;
F2,105=17, p<0.0001). Effects of fall grazing (Oct/Nov 2015)
onbiomass persisted into thesubsequentspring for nativegrass
plots(Figure 3b).Similar patterns wereapparent for controland
kochia plots, whereas herbicide plots maintained low biomass
acrossallthreegrazingtreatments(Figure3b;grazing×plottype
F2,119=7.7,p<0.0001).
Acrossseededplotsandcontrols,fallstandingbiomasswas23%
B. tectorum,74%forbs (mostly nonnativeannuals),and3%resident
nativegrasses(mostlyP. se cun da)byweight(SupportingInformation
TableS2).Springbiomassaveragedacrosscontrolsandseededplots
included60%B. tector um,22%forbs(mostlynonnativeannuals),17%
residentnativegrasses(mostlyP. sec und a),and0.5%seededspecies
(Suppor ting InformationTableS2).Grazingtreatments and interac-
tions amo ng grazing treat ments and plot t ypes had no signi ficant
effec ts on litter cover, invasive species cover, or invasive species
densityin2015or2016(allp-values>0.05;SupportingInformation
TableS3).
3.2 | Grazing treatments reduced seedling densities
The grazi ng×establis hment model reve aled that when c ompared to
densitiesinungrazedpaddocks,second-yeargrassandkochiaseedling
den sitie swere50%lowerinf al l-g ra zedan d36%lowerins pr ing-grazed
paddoc ks (Figure 4a , F2,4=7. 08, p=0.049). Plot s seeded w ith native
grasseshadalmost 12times more first-yearseedlingsofplanted spe-
cies than f orage kochia pl ots (Figur e 4b, F1,69=25.7,p<0. 0001) and 
ninetimes more second-yearseedlingsthaneitherunseeded controls
orforagekochiaplots(Figure4c,F2,121=31.9,p<0.0001).
FIGURE 3 Effectsofgrazingtreatmentsonstandingbiomass(a)
acrosssamplingdates(p-valuesrepresentthemaineffectofgrazing
foreachdate)and(b)acrossplottypesinMay2016(grazing×type
p<0.00 01).Control,orunseeded,plotsweremonitoredwithin
eachpaddock(acrossallthreegrazingtreatments).June2015was
priortograzing,November2015wasafterfallgrazing,andMay
2016wasafterspringgrazing.Withinasamplingdate,treatments
sharinglettersdonotdiffersignificantly(TukeyHSD).Different
capitalizationsandlettergroupsareusedtodifferentiateamong
resultsfromdifferentmodels.
    
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 7
PORENS KY Et a l.
3.3 | Restoration treatments muted negative
effects of grazing on seeded grasses
Theplantingstrategiesmodelindicatedthatacrossgrazingtreatments,
the highe r seed rate yield ed approximatel y twice as many fir st-year
grass se edlings and 1. 5 times as many seco nd-year seedlin gs as the
lower seed r ate (Figure 4 d,e; Year 1: F1,60=17.6, p<0.0 001; Year 2:
F1,53=14.9,p=0.0003).Bet weenyearoneandyeartwo,seedlingden-
sitiesdeclinedby36%inthelowand50%inthehighseedrateplots.
The planting strategies model also indicated a three-way in-
teraction among seed rate, grazing, and seed coating treatments
(F2,58=4.84,p=0.01)forsecond-yearseedlings.Tobetterunder-
stand thisinterac tion, separatemodelswereexaminedforcoated
anduncoatedseedtreatments.Uncoatedgrassseedsinungrazed
plotsproducedmoreseedlings thanuncoatedseedsineitherfall-
or spring-grazed plots, whereas fall- and spring-grazed plots had
similarseedling densities (Figure 5a;F2,4=8.39,p=0.04). Across
grazing treatments, seedlings from uncoated seeds were more
abundant in mixtures than monocultures (F1,52 =4.63, p=0.04),
andmoreabundantinhigh erthanlowerseedrateplots(Figure5a;
F1,52=11.81, p=0. 001). Grazing e ffects we re not influence d by
spatialplantingstrategyorseedrate(allinteractionp-values>0.05).
For coated se eds, differ ences among gr azing treatmen ts were
more muted.Among grazing treatments,the highest seedling den-
sitieswerefoundinspring-grazedplotsplantedathighrates,which
had signif icantly more seedlings t han spring-grazed plots pla nted
at low rates (F igure 5b; Gra zing×Seed rate F2, 53=4.60, p=0.01).
All other g razing and se ed rate combi nations pro duced interm edi-
ate seedli ng densities. Fo r coated seeds, mi xture plots pla nted at
high rates had more seedlings than mix ture plots planted at low
rates,whilemonocultureplotshad intermediate seedling densities
(Figure5b;Spatialarrangement×SeedrateF1,53=4.31,p=0.0 4).
3.4 | Species that produced the most seedlings were
also the most sensitive to grazing
Thegrass species modelshowed thatinyearone, averagedacross
seed rates, E. trachycaulus produced four to nine times as many
FIGURE 4 Overalleffectsof(a)
grazingtreatmentsinyear2,plottypes
in(b)year1and(c)year2,andseedrate
treatmentsin(d)year1and(e)year2on
seededspeciesdensities.Redbarsare
means,andboxplotsdisplayvariability.
Withineachpanel,treatmentssharing
capitallettersdidnotdiffersignificantly
inseedlingdensit y(TukeyHSD).In(c),all
herbicideplotshadzeroseedlings
(a)
A
B
C
(b)
A
B
A
BC
0
A
B
(c)
(e)
(d)
A
B
8 
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   PORENSKY Et a l.
seedlin gs as either Poa species, and E. elymoides produce d almost
fivetimesasmanyseedlingsasP. fendleriana(F i gur e 6 a,F4,270=33.0,
p<0.00 01).Bet weenyearsoneandtwo,Poaseedlingdensitiesdid
notchangeappreciably,butdensitiesofE. trachycaulusandV. m icro
stachyusdeclinedbyroughly50%, and densitiesofE. elymoides de-
clinedby>80%(Figure6b).Inyear two, E. trachycaulushad atleast
five timesasmanyseedlingsasE. elymoides,V. microstachyus,orP.
fendleriana, while P. s ecu n da  had intermediate seedling densities
(Figure6b,F4,247=34.5,p<0.0 001). Inyeartwo, wealsoobserved
two three-wayinterac tions in thegrass species model;oneamong
species, coating treatments, andgrazing treatments (F8,247=2.79,
p=0.006),andoneamongseedrates,coatingtreatments,andgraz-
ing treat ments (F2,30=5.19,p=0. 01). Individua l models were co n-
structedforeachspeciestobetterunderstandtheseinteractions.
ForallspeciesexceptE. elymoides,therewassomeevidencefor
athree-wayinteractionamongseedrate,seedcoating,andgrazing
treatments (E. trachycaulus F2,30=4.15, p=0.03, V. microstachys
F2,29=3.32, p=0.05,P. se cun da F2,30=3.22,p=0.05,P. fendleriana
F2,30=2.78,p=0.08). Forthree species(E. trachycaulus,P. se cu n da,
andP. fendleriana),theinteraction wasdriven bypoorperformance
of the low see d rate, uncoa ted, fall-gr azed treatm ent combinat ion
(Figure7).Forall fourspecies,somecombination ofcoating,higher
seed rate, or deferred grazing (spring-grazing or no-grazing) led to
highersecond-yearseedlingdensities,buteffectstrengthsvariedby
species(Figure7).ForE. trachycaulus,thehighestseedlingdensities
were foundin ungrazed or spring-grazed plot s planted at the high
ratewithcoatedseed.ForP. fendleriana,mosttreatmentshadsimilar
seedlingdensities,butdensities weremarkedly lower for uncoated
seedplantedinfall-grazed,lowrateplots,andcoatedseedplantedin
highrate,spring-orfall-grazedplots.Poa secundahadrelat ivelyhigh
seedlingdensitiesinalltreatmentcombinationsotherthanthefall-
grazed, uncoated,low ratecombination.Results forV. microstachys,
FIGURE 5 Seedlingdensitiesby
grazingtreatments,seedratesand
spatialarrangementsin(a)uncoated
and(b)coatedsubplots.Inuncoated
subplots,densitieswereaf fectedby
grazingtreatments,seedrates,and
spatialplantingarrangements(allmain
effectssignificant).Incoatedsubplots,
differencesamongtreatmentsweremore
muted(grazing×seedrateandspatial
arrangement×seedratesignificant)
Spatial arrangement and seed rate treatments
Low High Low High
mixturemonoculture
0
10
20
30
40
50
60
70
80
0
10
20
30
40
50
60
70
80
Grazing treatment
Fall
Spring
Ungrazed
(a) Uncoated seed
ungrazed >
(b) Coated seed
> (fall = spring)
mixture >> monoculture
> low ratehigh rate >
> spring grazed low ratespring grazed high rate >
> mixture low ratemixture high rate >
FIGURE 6 Densitiesof(a)first-year
and(b)second-yeargrassseedlingsby
speciesformonoculturestripplot s.
Redbarsaremeans.Withineachpanel,
densitiesofspeciessharingcapital
lettersdidnotdif fersignificantly(Tukey
HSD).ELEL:Elymus elymoides;ELTR:E.
trachycaulus;POFE:Poa fendleriana;POSE:
P. sec unda;andVUMI:Vulpia microstachys
(a) Year 1 (a) Year 2
AB
A
C
BC
ABC
B
A
BAB
B
    
|
 9
PORENS KY Et a l.
the only annual species, wereslightly different. Coatedseeds pro-
ducedhigherseedlingdensitiesinungrazedplotsthaninfall-grazed
plots, while uncoatedseeds hadinconsistent responses to grazing.
Acrosscoatingtreatments,ungrazed,highrateplotshadthehighest
second-yearseedlingdensities for V. microstachys.For all five spe-
cies,average seedlingdensitiesdidnot differsignificantly between
spring-grazedandungrazed plots(Figure7,SupportingInformation
TableS4).
4 | DISCUSSION
Interrupting the invasive grass-wildfire cycle in dryland ecosys-
tems is a chall enge worldwide , and is especiall y pressing in are as
like the Gre at Basin where e cosystem conve rsion has occu rred at
broad scales(DiTomaso,2000;Mack, 1981).Wehypothesizedthat
it might be p ossible to combine t argeted grazin g with high-input ,
spatially strategic restoration to create patches of self-sustaining,
fire-resistantvegetation.Thecreationofsuchpatchesiskeyforthe
long-termrecover yofdesiredecosystemfunctionsinhighlyinvaded
systems . In the first t wo years of this lo ng-term study, we found
thattargetedgrazingduringthefallorspringofthesecondgrowing
seasonreducedstandingbiomassbutalsoreduceddensitiesofspe-
cies plant ed in experim ental gree nstrips. D ensity redu ctions were
mitigatedby increasingseedingrates,delaying grazing, andselect-
inggrazing-tolerantspecies. Understandinghowinitial restoration
approachesandrepeatedgrazingtreatments influencefutureden-
sities of adultplantsatthis site requires longer-termobservations,
and future assessments areplanned. However,bec ausemor tality
risk declines substantially afterthe first or secondgrowing season
(Leger&Goergen,2017),second-yearresultscanprovideimpor tant
insights about how to a ddress seedling e stablishment, which has
been ide ntified as a cr itical re storatio n bottlen eck in dry land eco-
systems(Jamesetal.,2011).
FIGURE 7 Effectsofgrazing,seed
rateandseedcoatingtreatmentson
speciesplantedinmonoculturestripplots.
Three-wayinteractionsamonggrazing,
seedcoating,andseedratetreatments
weresignificantforElymus trachycaulus,
Poa secunda,andVulpia microstachys and
marginal(p=0.08)forP. fendleriana.See
Figure6foracronymdefinitions
10 
|
   PORENSKY Et a l.
4.1 | Tradeoff between reducing standing
biomass and seedling production
The flam mability of annu al grasses has in creased both th e fre-
quencyandintensityoffireininvadeddrylandsystems(Alba et
al., 2015; Bal ch et al., 2013; D’Antonio & Vit ousek, 1992). Our
experimentrevealedacleartradeof fbet weenreducingfuelloads
and restoring desirable grasses in invaded sagebrush steppe.
When resu lts were aver aged across al l planting tr eatment s, un-
grazedpaddockshadthehighestsecond-yearseedling densities,
but also th e highest st anding biomass a nd therefore th e great-
est fuel loads. The relative importance ofthese two factors for
the long-term persistenceof seeded species and their abilit y to
reducewildfirespreadremainsunclear.Forexample,earlyreduc-
tions in seedling density would not necessarily result in lower
densitiesofadult plants if competitionamong planted seedlings
isstrong(Mangla, Sheley,James, & Radosevich, 2011), and high
see dl ingde ns itieswi llnotreducefireri skinsite st hatbu rnbefor e
plantsreachadulthood.Contrarytoourprediction,ourdatasug-
gestthattargetedspring-grazing(deferreduntilthesecondyear)
in sites rece ntly seeded wit h native grasses may p rovide more
balance b etween the dual o bjectives of see dling establ ishment
andwildfireprotectionthan targeted fall grazing. Springgrazing
reduced standing biomassby50%butseedling densitiesbyonly
36%.Incontrast ,light-to-moderatefallgrazingatthestartofthe
second gr owing season red uced seedling de nsities by 50% and
biomass by only 30%–40%.The five-month deferment between
fall andspringgrazing may help to explain themilderimpact of
spring grazing; itispossible that older seedlings were more tol-
erant of defoliation, or that new green grow th of surrounding
vegetationinspringalteredgrazingpreferencesawayfromseed-
lings. Additionally,wetweather inspring 2016likelycontributed
toseedlingsurvival afterspring defoliation.Across bothgrazing
treatments, second-year seeding densities remained relatively
high(>10 per m2acrossmosttreatments).Basedonresultsfrom
our ungrazed plots, itseems likely that a longer (>1year)defer-
mentperiodwouldleadtohigherseedlingdensities,thoughsuch
atreatmentwouldalsolikelyincreasefuelloads.Overall,whilewe
observedthe expected directnegativeeffects on seedlings, tar-
geted grazingtreatments alsohad the expectedpositive ef fects
onfuelcharacteristics,and couldpotentiallyimproverestoration
outcomesoverthelong-termbyreducingcompetitionfrominva-
siveannualsandothernonseededspecies(seeindirectpathways
inFigure1).
Wh en co mpa red to na tiveg re ens tri pp l ot s ,p lot ss e ed edw it hko-
chiahadsimilarbiomassbutfewerseedlings,suggestingthatduring
the establishment phase, seeding with nativegrasses can produce
similarorevenbetterresultsintermsofseedlingsgrownperunitof
fuelload.Herbicidewasextremelysuccessfulatreducingfuelloads,
butprovidednootherecosystemser vices(e.g.,forageorbiodiver-
sity benefits).Without continuedmaintenance, it seemslikely that
thesebrownstripswillagainbecomedominatedbyinvasivespecies
(Merriametal.,2006).
4.2 | Strategic restoration to mitigate tradeoffs
In experimental greenstrip plot s, our analysis of planting strate-
gies reveal ed that several st rategies improved s eedling estab lish-
mentand/orminimizeddifferencesamonggrazingtreatments.The
most dramatic improvements in seedling density were achievedby
doublin g the seedin g rate, which al igns well with p revious stu dies
emphasizi ngth eimpor tan ceofp ro pa gu lepr es su reasa dr iv erofr es-
toration outcomes (Mazzolaetal., 2010; Schantz, Sheley,James,&
Hamerlynck,2016;Seabloom,Harpole,Reichman,&Tilman,2003).
In this study, beneficial effects of higher seed rates persisted into
thesecond growingseason,andminimized the negativeimpact sof
grazingtreatment s:se ed li ngde nsitie sinthehig hr at e,fa ll -orspring-
grazed pl ots were similar to de nsities in ungra zed, low rate plots
(Figure5).
Seed coating has been shown to improve plant establishment
in dryl and syste ms (Madsen, Dav ies, Boyd, Ker by,& Svejc ar,2016;
Madsen, Zvirzdin, Roundy, & Kostka, 2014). In this stu dy, coating
didnothave any significant main effects on seedlingestablishment.
Rather,itinteractedincomplexwayswithothertreatmentsandmay
have muted dif ferences among grazing treatments. For uncoated
seeds, ungrazed plots pro duced substantially more s eedlings than
either f all- or spring-gr azed plots (Fig ure 5). For coated see ds, the
highestseedlingdensitieswerefoundinspring-grazedandungrazed
plots planted at high rates, while most othergrazing and seed rate
combinationsproducedsimilarseedlingdensities(Figure5).Overall,
grazing treatments hada much weaker negative effect on seedling
densities in subplots planted with coated seeds. The sur factant
coating th at was applied to t he seeds has b een shown in prev ious
studiestoimproveseedlingsurvivalunderdroughtstress(Ahmedet
al.,2018;Madsen et al.,2012,2014; Madsen, Kostka,etal.,2016).
Wehypothesize thatinthis dryland studythe soil surfactant in the
coatinghelpedproducemorerobustplantsthatwereabletorecover
quickerafter thegrazing treatment. However,in ungrazed,highrate
plots,uncoatedseedlingdensitieswerehigherthancoatedseedling
densitie s (Figure 5). We hypothes ize that in these ungr azed plots,
coatedseedsweremature enoughtobegin self-thinningprocesses
duringthesecondgrowingseason.Thedevelopmentofseedcoating
technologiesforrangelandapplicationsareintheirinfancy;thisstudy
provides justification forfurtherresearchonhowcoatingtechnolo-
giesca nhe lps eededplant sovercomefactorsl imitingthei rsu cce ssi n
rangelandsystems.
We found that se ed mixtures p roduced more tot al seedlings
than monoculture applications, particularly when planted with
at high rate s. This patter n parallels r esults from s tudies in oth er
systems,whichhavefoundhighertot alcoverofseededspeciesin
mixturesduetohighcoverofafewdominantspecies(Porenskyet
al.,2012).Inthatwork,increasedcovercameattheexpenseofre-
duceddiversit yasweakercompetitorswereexcluded.Inthisstudy,
itwasimpossibletoassess diversityinmixtureplotsbecausespe-
ciesidentificationwasunreliable.However,giventheresults from
monoculture plots(Figure 7), it is likely that second-year seedling
communitiesinmixtureplotsweredominatedby themostprolific
    
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 11
PORENS KY Et a l.
seededspecies, Elymus trachycaulus. If this domi nant specie s is a
strongcompetitor,itwouldbeexpectedtobenefitfromlessintra-
specif ic an dm or ei nt er specifi ccom pe titioninmi x tu re pl ot s(Stol l&
Pr ati , 20 01;Tu rnb u ll , Coo m es, Pur ves,&Re e s,2 0 07) .Al tern ati vely,
mixtureplantingscouldincreaseseedlingabundanceacrossmulti-
ple species by reducing microsite-scale competition for the same
resources,ifintraspecificcompetitionisstrongerthaninterspecific
competi tion at the seed ling emergen ce stage (Leger & E speland,
2010).Futureassessmentswilldeterminewhetherincreasedseed-
ling densities in mixture plotsoccurredatthe expense ofspecies
diversity.
4.3 | Species‐level responses revealed
multiple strategies
Grasse s as a guild are hig hly grazing-tol erant, but s pecies dif fer
considerably in their responses to herbivory (Adler, Milchunas,
Lauenroth,Sala, &Burke,2004).Ourgrassspecies analysisdem-
ons tratedthattargetedgr az in gc anre du ceseedlingesta bl is hm en t
of several na tive grasses, a nd also revealed v ariation in spe cies
sensitivity to grazing treatments.Forexample,Elymus trachycau
luswasverysuccessfulatseedlingestablishment,butseedlings
showed the greatest negative response to both fall and spring
grazing treatments (Figure 7). Incontrast, Poa secunda produced
relativelyfewseedlingsinthefirstgrowingseason,butwasunaf-
fected by grazingand had high sur vival acrossalltreatments.By
thesecondgrowingseason,seedlingdensityofP. se cun dadidnot
differstatistically fromE. trachycaulus acrossgrazingtreatments
(Figure 6). Am ong the seed ed species, E. trachycaulus and P. se
cundamayrepresenttwoendsofasurvivalstrategygradient,in
whichsp eciesthatproducefe wersee dli ngsareals omoretolerant
ofdist ur bance ssuchasg ra zing(Briske,1996).Int hecaseofsmall-
staturedP. sec und a,grazing avoidancemightbea keyelementof
seedlingsuccess.
Itisimportanttonotethatourgrazingtreatmentsweregenerally
differentthan thosemost rangelandsexperience. Targeted grazing
isintended asavegetation management tool,not as at ypicalgraz-
ingsystem.Althoughpaddockswere~20hainsize,largerrangeland
areastypicallyoffergreaterdietaryandbehavioralchoicesforgraz-
inganimals.Thoughconcentrationofanimalsintosmallerpaddocks
is an effe ctive techn ique for redu cing biomass i n specific ar eas, it
can also limit diet preference choices andstimulate more uniform
acquisitionbehavior.Thus,ourresultsaremostrelevanttoprojects
that plan to use targeted grazing in smallerareas, suchasforfuels
reductionorfirebreakestablishment.Theappropriatenumbersand
timingoftargetedgrazingdoseswillvaryconsiderablywithprecipi-
tationamounts,seasonality,andperiodicityovertimeandspace.For
managersdesigninggrazingdoseapplicationsandsettingpostgraz-
ing residu al biomass t argets, we re commend con sidering th e local
availabil ity of grazing a nimals, potent ial biomass prod uction given
recent and forecasted precipitation,thephenology and palatability
oftargetedspecies,andthephenologyandpalatabilityofco-occur-
ringdesirablespecies.
5 | CONCLUSIONS
Innovativemanagement and restoration approaches are neededto
pr eve ntt h eco nti n ued l oss of d esi r ede cos y s te m ser vi ces ins a ge b r ush
steppe,oneofNorthAmerica’smostthreatenedecosystems(Davies
etal.,2011).In systemsthreatened byinvasive plantsand increased
wildfir e frequen cy,li vestock c an provide op portuni ties for ta rgeted
vegetationmanagement,andrestorationtreatment scanaffectseed-
ling responses tograzing. Understanding hownonnative plants and
animals interactcan facilitate theuse of herbivores as management
tools to infl uence plant comm unity compo sition in ways that f avor
desirable species and reduce problematic ones(Davies etal., 20 09;
Mart y, 20 05). We explored interactions between targeted grazing
and seed ling establish ment, which has be en identified as a c ritical
bottleneck for restoration in dryland areas where annual invasive
grassesarehighlycompetitivewithmoredesirablespecies(Jameset
al.,2011).Thoughfutureassessmentsareneededtoclarifylong-term
outcomes,ourstudyidentifiedcleartradeoffs betweenestablishing
native pla nts and using li vestock to redu ce the spread of w ildfires,
andalsodemonstratedthatpotentiallyundesirabletradeoffs canbe
minimized byboos tings eed rateso rusing grazing-tolerant species.
Ourresultsindicatethatsimilar effortstouse targeted grazing as a
restorationtoolinotherdrylandsystemsshouldincorporatearange
ofspecies in initial trials, and consider seeding at higherrates when
grazinganimalsareintroducedduringseedlingestablishment.
ACKNOWLEDGMENTS
WethanktheElkoLandandLivestockCompanyandNewmontMining
Corpor ation for providin g facilities, la bor,a nd permission for t his re-
search.Forfieldanddataassistance,wearegratefultoOwenBaughman,
Jason Spr ott, Scot Ferg uson, Marenn a Disbro, Quinn C ampbell, El eni
Nicholson, Sarah Barga, Bryce Wehan, Sage Ellis, Erick L arsen, Jen
Peter son,andB rianVonSeg gern.FundingwasfromaNationalIns titute
ofFoodandAgriculture,U.S.DepartmentofAgricultureawardwithinthe
WesternIntegratedPestManagementprogram(2013-34103-21325).
CONFLICT OF INTEREST
Nonedeclared.
AUTHOR CONTRIBUTIONS
Conceivedanddesigned experiment:LMP,EAL,MAW,BLP,MDM.
Performedexperiment:LMP,EAL,MDM,BLP,MAW.Analyzeddata:
LMP.Interpreted resultsand draftedmanuscript: LMP,EAL, MAW.
Revisedmanuscriptandapprovedsubmission:LMP,EAL,MDM,BLP,
MAW.
DATA ACCESSIBILITY
Data on seedling densities, biomass and cover will be stored on
Dryadbeforepublication.
12 
|
   PORENSKY Et a l.
ORCID
Lauren M. Porensky http://orcid.org/0000-0001-6883-2442
Matthew A. Williamson http://orcid.org/0000-0002-2550-5828
Matthew D. Madsen http://orcid.org/0000-0003-1398-8655
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SUPPORTING INFORMATION
Additional supporting information may be found online in the
Suppor tingInformationsectionattheendofthearticle.
How to cite this article:Porensk yLM,PerrymanBL,
WilliamsonMA,MadsenMD,LegerEA .Combiningactive
restorationandtargetedgrazingtoestablishnativeplants
andreducefuelloadsininvadedecosystems.Ecol Evol.
2018 ;0 0:1–14 . https://doi.org/10.1002/ece3.4642
... Efforts to control exotic annual grasses and reestablish native plant communities have also often been unsuccessful (Young 1992;Monaco et al., 2005;Davies et al., 2015). However, there is some evidence that highly targeted or resource-intensive treatments can result in greater success (Porensky et al., 2018;Davidson et al., 2019). Given the economic constraints to implementing intensive treatments across wide areas, a more strategic approach must be applied to stem the continued conversion of sagebrush rangelands to exotic annual grasslands and prioritize where limited restoration resources should be applied. ...
... In addition, the reduction of litter associated with dormant-season grazing of exotic annual grasses can decrease their seedbank and reduce safe sites for germination, and this method has shown some promise for promoting perennials in exotic annual grasslands (Schmelzer et al., 2014;Perryman et al., 2020). Furthermore, it is possible that targeted grazing in combination with seeding of grazing-tolerant perennial species could begin to transition some of these highly invaded sites back to perennial dominance (Porensky et al., 2018). ...
Article
Exotic annual grasses dominate millions of hectares and increase fire frequency in the sagebrush ecosystem of North America. This devastating invasion is so costly and challenging to revegetate with perennial vegetation that restoration efforts need to be prioritized and strategically implemented. Management needs to break the annual grass-fire cycle and prevent invasion of new areas, while research is needed to improve restoration success. Under current land management and climate regimes, extensive areas will remain annual grasslands, because of their expansiveness and the low probability of transition to perennial dominance. We propose referring to these communities as Intermountain West Annual Grasslands, recognizing that they are a stable state and require different management goals and objectives than perennial-dominated systems. We need to learn to live with annual grasslands, reducing their costs and increasing benefits derived from them, at the same time maintaining landscape-level plant diversity that could allow transition to perennial dominance under future scenarios. To accomplish this task, we propose a framework and research to improve our ability to live with exotic annual grasses in the sagebrush biome.
... To date, grazing effects have largely been confined to comparing one grazing management strategy with ungrazed areas ( Davies & Boyd 2019 ), despite strong evidence that the effects of grazing on plant communities depend on grazing management ( Davies et al. 2016 ;Souther et al. 2019 ). Furthermore, knowledge of the timing, intensity, and duration of grazing is often lacking, making it difficult to critically evaluate and compare effects across studies (but see Davies et al. 2017 ;Porensky et al. 2018 ). This is particularly of concern for making management recommendations for fire suppression through fine fuel load reduction. ...
Article
Wildfire activity is accelerating on many rangelands worldwide, yet the potential for grazing to be used as a fire management tool remains largely unknown. Particularly, little is known about the influence of grazing on ignition and initial spread of fire, as well as how these vary by differences in grazing management. We investigated effects of grazing intensity (light, moderate, high) on fuel characteristics, fire ignition, and initial spread during the wildfire season in a native-dominated shrub steppe in eastern Oregon. We found that differences in grazing intensity have differential effects on fuel profiles (cover, height, moisture, biomass) with resulting impacts on fire behavior, but these relationships varied across study years. In particular, grazing had a stronger effect on ignition probability in drier years. Fire behavior in lightly grazed plots were similar to ungrazed plots, while moderate grazing was similar to high-intensity grazing. Results of this study highlight that grazing can be useful as a tool for wildfire management, and grazing at moderate and high intensities can reduce the probability of fire propagation in native-dominated sagebrush ecosystems. Further, the effects of grazing are context dependent and therefore may depend on specific objectives and environmental conditions.
... Furthermore, the interactive effects of grazing and fire to restore native grassland species are shown where fire can promote native forb recovery but grazing is necessary to maintain restoration outcomes [15]. Moderate livestock grazing decreases the risk of wildfires in semi-arid and arid rangelands [16,17], supporting the incorporation of herbivory into fuel management practices in areas of high herbaceous productivity to increase the effectiveness of fuel treatments [18]. Examples are also found in East African environments where the interaction of fire and cattle prevents the degradation of ericaceous communities [19]. ...
Article
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Extensive livestock grazing has proved to be a valuable tool to reduce wildfire risk in Mediterranean landscapes. Meat from herds providing wildfire prevention services exhibit sustainability traits that can appeal to ethical consumers and find a suitable niche in local markets. This study assesses the preferences of a consumer sample in the province of Girona (north-eastern Spain) for different lamb meat labeling options from herds providing wildfire prevention services. The aim is to disentangle consumer profiles, providing evidence for improved product labeling. This may increase the added value and the viability of small farms providing this service. Employing a latent class modeling approach, we explore how meat consumption patterns and socioeconomic features may contribute to explain preferences for different meat labeling options. Our results have identified three consumer profiles: traditional rural consumers relying on trust with producers, younger consumers more akin to new labeling schemes, and urban consumers that support local butchers as a trusted information source. Different labeling mechanisms may work in a complementary way to arrive to different audiences of potential consumers. Geographical indication labels can serve as a good departure point, complemented with information cues on environmental factors related to wildfire protection.
... Herbivores are often drawn to burned areas (Allred et al., 2011;Archibald et al., 2005;Klop et al., 2007;Sensenig et al., 2010;Vinton et al., 1993), to feed on nutritious flushes of fresh regrowth (Foster et al., 2015), as well as on the newly established more palatable species (Greene et al., 2012), but perhaps also for increased antipredator visibility (Eby et al., 2014). Conversely, herbivory by large mammals can decrease fuel loads (Foster et al., 2020;Porensky et al., 2018) and fire intensity (Hobbs et al., 1991, Kimuyu et al., 2014, reviewed in Johnson et al., 2018and Foster et al., 2020, even to the extent of suppressing fire completely (Johansson et al., 2020;Kimuyu et al., 2014;Liedloff et al., 2001). This effect is strong enough that the use of livestock has been proposed as a tool to mitigate fire risk (Bailey et al., 2019;Nader et al., 2007). ...
Article
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Fire, herbivores, and climatic factors are all major drivers of savanna and grassland dynamics, and they interact in complex ways, which are still in the process of being explored. In particular, herbivores can reduce fire intensity by removal of biomass, and this could be reinforced by herbivores’ attraction to recently burned sites, although grassland resilience may limit the temporal depth of such effects. Fire temperature is the most common fire metric reported for grassland fire, but additional aspects of fire behavior can also be measured. Using a set of controlled, replicated experiments, we examined the effects of year of burn, herbivory by livestock and wildlife, previous burn, and weather history on fire behavior in an African savanna. Multiple measures of fire behavior (minimum fire temperature, flame front speed, fire residence time, maximum flame height, and flame length) in 36 controlled burns were positively intercorrelated. Burns conducted in 2018 were significantly cooler, especially at heights >0.5 m above the ground, than those in 2013, a wetter year with more grass fuel. Grass fuel loads and fire temperatures were reduced by the presence of livestock and wildlife. Our sampling methods did not for the most part reveal expected differences in fire temperatures or other behaviors between the reburned plots and those burned for the first time in 2018, with or without herbivores, suggesting strong postfire resilience in this semiarid savanna rangeland.
... For example, nearly a century after abandonment, certain abandoned green lands in the States have only 75% of the plant diversity of surrounding natural flora [6]. Plant diversity management through active restoration is frequently adopted, as indicated by the widespread use of monocultures in global reforestation initiatives [7]. In many areas, long-term changes in land use have an impact on vegetation structure and habitat. ...
... Ideally, the outcome of management should be the restoration of areas of native vegetation, rather than simply the reduction of biomass in the short term. Although this requires greater effort initially, the level of maintenance long term will be reduced, and the resulting natural green breaks (Hulvey et al. 2017;Porensky et al. 2018) can provide multiple additional, measurable benefits for wildlife . In Australia, and elsewhere where ecosystems have evolved without heavy grazing by large herbivores, the use of livestock grazing as a conservation tool is controversial, even (or especially) at sites that were previously heavily grazedlike Tjoritja. ...
Article
Full-text available
Background Large old trees are keystone structures of terrestrial ecosystems that provide unique habitat resources for wildlife. Their widespread decline worldwide has serious implications for biodiversity and ecosystem integrity. In arid regions, large trees are relatively uncommon and often restricted to areas with elevated soil moisture and nutrients. Introduced grasses, now pervasive in many dryland environments, also thrive in such areas and are promoting more frequent and intense fire, potentially threatening the persistence of large trees. Here we report on the impact of a single wildfire on large river red gums ( Eucalyptus camaldulensis Dehnh.) in arid riparian woodland invaded by buffel grass ( Cenchrus ciliaris L.), a serious invader of desert ecosystems worldwide. In 2018, 266 trees with > 80 cm equivalent trunk diameter were mapped at six sites to provide a ‘pre-fire’ baseline. Within a year, the sites were impacted by a large, unprecedented wildfire that burnt an area of 660 km ² ha in 15 days. Sites were resurveyed in February 2019 to assess the fate of the trees. Reference to fire severity, calculated from remote-sensed imagery, is provided for additional context. Results In total, 67 trees, 27% of all large trees at the sites were destroyed. If trees in unburnt patches are excluded, 54% of trees exposed to the fire were destroyed and the remainder lost on average 79% of their canopy. Conclusions This severe detrimental effect of a single fire, on trees estimated to be centuries old, is indicative of tree-loss occurring across remote arid Australia in habitats where fire is now fuelled predominantly by invasive grasses. Large volumes of novel grass fuels along creeklines in combination with extreme weather events were major factors driving the spread, extent and impacts of the wildfire we report on and are causing a shift from relatively uncommon and predictable, rainfall-dependent large wildfires to large, severe fires that can occur anytime. We predict further decline in the abundance of large trees from similar fires will occur widely throughout arid Australia over the next decade with substantial long-term impacts on multiple species. New strategies are urgently required to manage fire in invaded arid ecosystems to better protect large trees and the critical resources they provide.
... Several authors found a strong influence of seasonal grazing on vegetation (Shen et al. 2011;Wu et al. 2014;Porensky et al. 2018). However, this was not the case in the current study, because plant responses to grazing in the winter pasture were comparable to the summer pasture although the north-facing slopes had higher plant cover, plant density and biomass production. ...
Article
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Tajikistan’s rangelands are mostly mountainous and consist of summer and winter pastures. Vegetation structure and composition in these diverse landscapes are generally influenced by environmental factors. The objective of this study was to assess the effects of aspect on vegetation characteristics of two mountainous pastures (summer and winter) over two seasons (autumn and spring) in Tajikistan. A three-way ANOVA was conducted using GLM procedures to test the main effects and interactions of these factors on vegetation attributes. The biomass production (kg DM ha⁻¹) was significantly greater on the north-facing aspects for both summer and winter pastures in spring (483.4, 326.1) and autumn (57.2, 143.9), compared with south-facing aspects (57.2, 143.9 in spring and 18.5, 48.2 in autumn, respectively). Plant cover and plant density were also greater on north than south-facing slopes for summer and winter pastures in spring and autumn. Aspect significantly affected species diversity, botanic composition, and plant life forms of both pastures mainly for grasses and geophytes. There were greater vegetation responses on north than south-facing slopes, implying that aspect is important when designing mountain rangeland restoration. Given this complexity, land managers should thoroughly assess the conditions of the target site before defining restoration objectives and interventions.
... Green firebreaks are strips of vegetation with low flammability grown at strategic locations in the landscape and are increasingly being used world-wide to manage fire (Cui et al., 2019). The use of restored native vegetation as native green firebreaks to disrupt fire invasion feedbacks in invaded dryland environments is a more novel concept (Porensky et al., 2018) that has the advantage of simultaneously supporting the persistence of native plant communities and providing resource 'islands' for native fauna. In areas invaded with buffel grass, experimentation with green breaks of similar size to standard fire breaks would be worthwhile, with priority given to areas with significant natural and cultural heritage, and areas where long-lived trees with high habitat value may be at risk (Schlesinger and Judd 2019;Westerhuis et al., 2019). ...
Article
Full-text available
Introduced grasses are a major threat to dryland ecosystems world-wide because of their ability to transform plant communities and change fire regimes. These structural and functional shifts are often assumed to impact wildlife but this has rarely been measured directly. Likewise, evaluation of weed removal programs rarely considers benefits to fauna, thereby limiting information that could inform management decisions. We used an experimental approach to test the impacts of removing invasive buffel grass (Cenchrus ciliaris), a globally significant invader of dryland systems, on reptiles, a prominent component of the Australian desert fauna. A combination of mechanical and herbicide treatment was applied to replicate plots in areas that had been invaded for at least two decades and changes to ground cover and plant and reptile assemblages were monitored over six years and compared to still-invaded control plots. Following treatment, native plants re-established without the need for reseeding or planting, especially during a period of high rainfall, when positive effects on reptiles also became apparent. The abundance and species richness of reptiles increased at all plots during the mesic period, but less so in control plots, and remained higher at treated plots thereafter, although this was only significant at some times. Post-treatment 27 of 36 species were captured more frequently in treated plots and only four species, all with very low captures, were captured more often in invaded control plots. This consistent trend among species suggests negative impacts of buffel grass on reptiles are likely caused by broad factors such as reduced prey or habitat diversity. Together with concurrent research at the same sites, our results provide experimental evidence that removing buffel grass from heavily invaded areas, even at small scales, benefits a variety of native flora and fauna. Until landscape-scale options are available, restoration of smaller areas within buffel-invaded landscapes can help to preserve native seed banks and adult plants, reduce fire impacts, and provide patches of favourable habitat for fauna. The creation of ‘islands’ of restored native vegetation deserves further consideration as an effective intervention that could help to achieve short and long-term conservation goals in grass-invaded dryland ecosystems.
... For example, it was found that some abandoned farmlands in the USA had only 75% of plant diversity relative to surrounding natural vegetation nearly a century after abandonment [14]. Managing for plant diversity by means of active restoration has not been widely practiced in restorations, as evidenced in the dominant use of monocultures in global revegetation efforts [15,16]. ...
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In recent years, the phenomenon of abandonment of arable fields has increased in Saudi Arabia due to low soil fertility, drought, low rainfall, high levels of evapotranspiration, soil salinization, and low level of groundwater. We evaluated the effect of agricultural land abandonment on soil properties, perennial vegetation composition, and population structure in the Al-Kharj region, Saudi Arabia. A total of 11 perennial plant species belonging to 9 families and 11 genera were detected in the different abandoned fields of the study area. Four plant communities were identified after the application of the detrended correspondence analysis (DCA) ordination. The indicator species were (1) Seidlitzia rosmarinus—Zygophyllum hamiense, (2) Traganum nudatum—Seidlitzia rosmarinus, (3) Traganum nudatum—Prosopis farcta, and (4) Calligonum comosum—Pulicaria undulata. Results of the soil analysis showed significant differences in soil texture, pH, salinity, and nutrient content among the four recognized plant communities. Demographic analysis indicated that populations of Zygophyllum hamiense and Calligonum comosum tended to be either inverse J-shaped or positively skewed which may have indicated rapidly-growing populations with high reproductive capacity. Conversely, the size–frequency distribution of Traganum nudatum, S. Rosmarinus, and Prosopis farcta was approximately symmetrical (i.e., bell-shaped). The present study sheds light on the necessity of managing abandoned agricultural fields for restoring and improving rangelands with native species that are adapted to the local conditions such as low water demand.
Article
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On the Ground •More often than not, there is untapped potential for win-wins between livestock production and conservation. On the other hand, it is impossible to achieve every objective everywhere, all the time. Sometimes the tradeoffs are real. •We need to spend less time searching for general rules and more time embracing the complexity and context-dependence within rangeland science. •Rather than writing off findings that do not fit our current worldview, we should challenge ourselves to broaden our views in ways that reconcile multiple findings or multiple truths. It is possible we are all partly or mostly right, and we just need to figure out why, how, and in what contexts. •There is value in doing research in a way that focuses on really listening to and respecting multiple perspectives so that the results we produce not only qualify as facts, but also as truths that many people can buy into and get behind.
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Cheatgrass (Bromus tectorum) is an invasive grass pervasive across the Intermountain Western US and linked to major increases in fire frequency. Despite widespread ecological impacts associated with cheatgrass, we lack a spatially extensive model of cheatgrass invasion in the Intermountain West. Here, we leverage satellite phenology predictors and thousands of field surveys of cheatgrass abundance to create regional models of cheatgrass distribution and percent cover. We compare cheatgrass presence to fire probability, fire seasonality and ignition source. Regional models of percent cover had low predictive power (34% of variance explained), but distribution models based on a threshold of 15% cover to differentiate high abundance from low abundance had an overall accuracy of 74%. Cheatgrass achieves ≥ 15% cover over 210,000 km² (31%) of the Intermountain West. These lands were twice as likely to burn as those with low abundance, and four times more likely to burn multiple times between 2000 and 2015. Fire probability increased rapidly at low cheatgrass cover (1–5%) but remained similar at higher cover, suggesting that even small amounts of cheatgrass in an ecosystem can increase fire risk. Abundant cheatgrass was also associated with a 10 days earlier fire seasonality and interacted strongly with anthropogenic ignitions. Fire in cheatgrass was particularly associated with human activity, suggesting that increased awareness of fire danger in invaded areas could reduce risk. This study suggests that cheatgrass is much more spatially extensive and abundant than previously documented and that invasion greatly increases fire frequency, even at low percent cover.
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While much research has documented the impact of invaders on native communities and ecosystem services, there has been less work quantifying how invasion affects the genetic composition of native populations. That is, when invaders dominate a community, can they shift selection regimes and impact the evolutionary trajectory of native populations? The invasion of the annual grass Bromus tectorum in the Intermountain West provides an opportunity to quantify the effects of invasion on natural selection in wild populations. The shift from a perennial-dominated native community to one dominated by a highly competitive annual species alters the timing and intensity of competitive pressure, which has the potential to strongly shift selection regimes for native plants. To quantify traits under selection in contrasting environments, we planted seeds of two native perennial grasses, Elymus multisetus and Poa secunda, into three invaded, invaded but weeded and relatively uninvaded sagebrush systems. We quantified phenotypic traits of seedlings from separate maternal plants, describing differences in phenotypes among individuals. We then asked which traits were associated with survival and plant size in adjacent invaded and uninvaded sagebrush systems, following individual seed performance for 3 years. We found evidence for divergent selection between invaded and uninvaded sagebrush systems, with contrasting phenotypic traits associated with greater survival or plant size in these different growing conditions at all three field sites. For example, at one field site, P. secunda families with higher root tip production were more likely to survive in invaded and weeded environments, but this was not the case in uninvaded environments. Similarly, for E. multisetus, root mass fraction, seed mass and allocation to coarse or fine roots affected survival and plant size, again with contrasting relationships across invaded, weeded or uninvaded environments. Synthesis. Impacts of invasive species extend beyond ecosystem and community composition changes and can affect the evolutionary trajectory of native populations. By quantifying natural selection in invaded landscapes, we identified phenotypic traits that are potentially adaptive in these invaded systems. Importantly, these traits differed from traits associated with success in uninvaded communities. This insight into adaptive, contemporary evolution in native species can guide restoration and conservation efforts. © 2017 The Authors. Journal of Ecology
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Rangelands occupy over a third of global land area, and in many cases are in less than optimum condition as a result of past land use, catastrophic wildfire, and other disturbances, invasive species, or climate change. Often the only means of restoring these lands involves seeding desirable species, yet there are few cost effective-seeding technologies, especially for the more arid rangeland types. The inability to consistently establish desired plants from seed may indicate that seeding technologies being employed are not successful in addressing the primary sources of mortality in the progression from seed to established plant. Seed enhancement technologies allow for the physical manipulation and application of materials to the seed that can enhance germination, emergence, and/or early seedling growth. In this article, we examine some of the major limiting factors impairing seedling establishment in North America’s sagebrush steppe ecosystem and propose seed enhancement technologies that may have the potential to overcome these restoration barriers.We discuss specific technologies for: (1) increasing soil water availability; (2) enhancing seedling emergence in crusting soil; (3) controlling the timing of seed germination; (4) improving plantability and emergence of small-seeded species; (5) enhancing seed coverage of broadcasted seeds; and (6) protecting seedlings from pre-emergent herbicide. Concepts and technologies in this article for restoring the sagebrush steppe ecosystem may apply generally to semiarid and arid rangelands around the globe.
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Restoration islands are concentrated plantings in strategic locations, created to efficiently use resources to achieve restoration goals. These methods have been used effectively in mesic ecosystems, particularly tropical forests, where the goal of island plantings is often to “nucleate” across a degraded area, providing a seed source for spread outside the planted area. Here, we consider how an island strategy might be used to achieve restoration goals in dryland ecosystems, where limited resources and large areas of degraded land make restoration extremely challenging. In contrast to more productive areas, spread or “nucleation” from restoration islands in drylands may not occur or occur more slowly than required by most management time frames. Despite this, small-scale, more intensive island plantings may still be useful for achieving short-term goals, such as weed control, fire management, erosion control, and creation of wildlife habitat. Over the long term, island plantings could serve the same nucleation function as in other ecosystems and serve as repositories for genetic diversity within highly fragmented native systems. Here, we highlight the opportunities for using these high-intensity, targeted planting methods in dryland ecosystems, provide the guidelines for establishing islands to achieve short- and long-term restoration goals, and identify the areas where additional research is needed to understand the value of restoration islands in dryland ecosystems.
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Arid ecosystems are often vulnerable to transformation to invasive-dominated states following fire, but data on persistence of these states are sparse. The grass/fire cycle is a feedback process between invasive annual grasses and fire frequency that often leads to the formation of alternative vegetation states dominated by the invasive grasses. However, other components of fire regimes, such as burn severity, also have the potential to produce long-term vegetation transformations. Our goal was to evaluate the influence of both fire frequency and burn severity on the transformation of woody-dominated communities to communities dominated by invasive grasses in major elevation zones of the Mojave Desert of western North America. We used a chronosequence design to collect data on herbaceous and woody cover at 229 unburned reference plots and 578 plots that burned between 1972 and 2010. We stratified the plots by elevation zone (low, mid, high), fire frequency (1–3 times) and years post-fire (YPF; 1–5, 6–10, 11–20 and 21–40 YPF). Burn severity for each plot was estimated by the difference normalized burn ratio. We identified two broad post-fire successional pathways. One was an outcome of fire frequency, resulting in a strong potential transformation via the grass/fire cycle. The second pathway was driven by burn severity, the critical aspect being that long-term transformation of a community could occur from just one fire in areas that burned at high or sometimes moderate severity. Dominance by invasive grasses was most likely to occur in low-and high-elevation communities; cover of native herbaceous species was often greater than that of invasive grasses in the mid-elevation zone. Synthesis. Invasive grasses can dominate a site that burned only one time in many decades at high severity, or a site that burned at low severity but multiple times in the same time period. However, high burn severity may predispose areas to more frequent fire because they have relatively high cover of invasive annual grass, suggesting burn severity and fire frequency have both independent and synergistic effects. Resilience in vegetation structure following fire in many arid communities may be limited to a narrow window of low burn severity in areas that have not burned in many decades. Published 2017. This article is a U.S. Government work and is in the public domain in the USA
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The interaction between grazing and fire influences ecosystems around the world. However, little is known about the influence of grazing on fire, in particular ignition and initial spread and how it varies by grazing management differences. We investigated effects of fall (autumn) grazing, spring grazing and not grazing on fuel characteristics, fire ignition and initial spread during the wildfire season (July and August) at five shrub steppe sites in Oregon, USA. Both grazing treatments decreased fine fuel biomass, cover and height, and increased fuel moisture, and thereby decreased ignition and initial spread compared with the ungrazed treatment. However, effects differed between fall and spring grazing. The probability of initial spread was 6-fold greater in the fall-grazed compared with the spring-grazed treatment in August. This suggests that spring grazing may have a greater effect on fires than fall grazing, likely because fall grazing does not influence the current year's plant growth. Results of this study also highlight that the grazing-fire interaction will vary by grazing management. Grazing either the fall or spring before the wildfire season reduces the probability of fire propagation and, thus, grazing is a potential fuel management tool.
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Woody plant encroachment can increase nutrient resources in the plant-mound zone. After a fire, this zone is often found to be water repellent. This study aimed to understand the effects of post-fire water repellency on soil water and inorganic nitrogen and their effects on plant growth of the introduced annual Bromus tectorum and native bunchgrass Pseudoroegneria spicata. Plots centered on burned Juniperus osteosperma trees were either left untreated or treated with surfactant to ameliorate water repellency. After two years, we excavated soil from the untreated and treated plots and placed it in zero-tension lysimeter pots. In the greenhouse, half of the pots received an additional surfactant treatment. Pots were seeded separately with B. tectorum or P. spicata. Untreated soils had high runoff, decreased soil-water content, and elevated NO3–N in comparison to surfactant treated soils. The two plant species typically responded similar to the treatments. Above-ground biomass and microbial activity (estimated through soil CO2 gas emissions) was 16.8-fold and 9.5-fold higher in the surfactant-treated soils than repellent soils, respectably. This study demonstrates that water repellency can influence site recovery by decreasing soil water content, promoting inorganic N retention, and impairing plant growth and microbial activity.
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Interannual variability in burn severity is assessed across forested ecoregions of the western United States to understand how it is influenced by variations in area burned and climate during 1984-2014. Strong correlations (r>0.6) between annual area burned and climate metrics were found across many of the studied regions. The burn severity of individual fires and fire seasons was weakly, but significantly (P<0.05), correlated with burned area across many regions. Interannual variability in fuel dryness evaluated with fuel aridity metrics demonstrated weak-to-moderate (r >0.4) relationships with regional burn severity, congruent with but weaker than those between climate and area burned for most ecoregions. These results collectively suggest that irrespective of other factors, long-term increases in fuel aridity will lead to increased burn severity in western United States forests for existing vegetation regimes.