Western North American Naturalist Western North American Naturalist

Volume 67 Number 2 Article 13

6-20-2007

Effects of prescribed fall burning on a wetland plant community, Effects of prescribed fall burning on a wetland plant community,

with implications for management of plants and herbivores with implications for management of plants and herbivores

Scott R. McWilliams University of California, Davis

Todd Sloat University of California, Davis

Catherine A. Toft University of California, Davis

Daphne Hatch California Department of Parks and Recreation, Northern Regional Headquarters, Santa Rosa, California

Follow this and additional works at: https://scholarsarchive.byu.edu/wnan

Recommended Citation Recommended Citation McWilliams, Scott R.; Sloat, Todd; Toft, Catherine A.; and Hatch, Daphne (2007) "Effects of prescribed fall burning on a wetland plant community, with implications for management of plants and herbivores," Western North American Naturalist: Vol. 67 : No. 2 , Article 13. Available at: https://scholarsarchive.byu.edu/wnan/vol67/iss2/13

This Article is brought to you for free and open access by the Western North American Naturalist Publications at BYU ScholarsArchive. It has been accepted for inclusion in Western North American Naturalist by an authorized editor of BYU ScholarsArchive. For more information, please contact scholarsarchive@byu.edu, ellen_amatangelo@byu.edu.

Adaptive management is designed to trans-form natural resource management from a sys-tem based upon uncertainty, derived mostlyfrom descriptive studies, to one based on pro-gressively more accurate scientific knowledge,derived mostly from experimental studies (Hol-ling 1978, Walters 1986, Walters and Holling1990). The practice of adaptive managementrequires monitoring and evaluating outcomesof a management activity, and readjusting futuremanagement accordingly (Gibbs et al. 1999).Ideally, management and monitoring are de-signed so that direct effects of managementactivity can be assessed along with how theseeffects are influenced by interactions with otherimportant abiotic and biotic factors (Pickettand Ostfeld 1995). Here we assess effects ofprescribed fall burning on a wetland plant com-

munity and use of the wetlands by migratingarctic-nesting geese during spring. Consistentwith our goal of adaptive management, we usedan experimental design and analysis that allowedus to determine how the effects of burning onthe wetland plant community were contingenton other important ecological factors.

Prescribed burning and livestock grazinghave been used to reduce residual plant mate-rial in wetlands so that newly emerging plantsin the spring are available to herbivorous water-fowl, such as geese (Hanson 1939, Lynch 1941,Goodwin 1979, Smith and Kadlec 1985a, 1985b,Weller 1994). Prescribed burning is often pre-ferred to grazing because it does not involveintroduced mammals that require regular atten-tion, and because fire may reduce the relativeabundance of introduced and undesirable plant

Western North American Naturalist 67(2), © 2007, pp. 299–317

EFFECTS OF PRESCRIBED FALL BURNING ON A WETLAND PLANT COMMUNITY, WITH IMPLICATIONS

FOR MANAGEMENT OF PLANTS AND HERBIVORES

Scott R. McWilliams1,2,4, Todd Sloat1,5, Catherine A. Toft2, and Daphne Hatch3,6

ABSTRACT.—An important contemporary challenge for adaptive resource management is assessing both the directand indirect effects of management activities by designing appropriate monitoring programs and sound analysis meth-ods. Here we evaluate the effects of prescribed fall burning on a wetland plant community that is managed primarily forspring-migrating geese. During late fall in 2 consecutive years, we burned vegetation in 4 replicate blocks (2.3 ha each)that traversed a natural moisture and associated vegetation gradient. We used ordination, gradient analysis, and contin-gency table analysis to evaluate how annual changes in relative abundance of plants were affected by burning as well asother important ecological factors. Burning increased species diversity of plants, especially in the 2 wetter vegetationzones, but had no effect on species richness or on the proportion of native plant species. Wetland plant speciesresponded to prescribed burning independently, and their response often differed by vegetation zone and with annualvariation in flooding. Burning enhanced the abundance of native foxtail barley (Hordeum jubatum) and reduced theabundance of introduced swamp timothy (Crypsis shoenoides). Saltgrass (Distichlis spicata), a native plant species, wasusually less abundant following burning, although the level of response was different for each of the 3 vegetation zones.Two other introduced plant species, quackgrass (Elytrigia repens) and reed canarygrass (Phalaris arundinaceae), wereless abundant after fall burning, especially when spring flooding was more extensive. Wild geese using the experimentalblocks for feeding clearly preferred burned sites, suggesting that fall burning can enhance wetland use by geese duringspring. Given that simple manipulations such as burning and flooding of a wetland system may often produce complexresults, we suggest that on-going management schemes be regularly evaluated with field experiments such as those con-ducted in this study.

Key words: adaptive management, CANOCO, correspondence analysis, fire, geese, prescribed burning, wetland plantcommunity.

1Department of Wildlife, Fish, and Conservation Biology, University of California, Davis, CA 95616-8755.2Section of Evolution and Ecology, Division of Biological Sciences, University of California, Davis, CA 95616-8755.3California Department of Parks and Recreation, Northern Regional Headquarters, Santa Rosa, CA 95401-4653.4Present address: Department of Natural Resources Science, University of Rhode Island, Kingston, RI 02881. E-mail: srmcwilliams@uri.edu5Present address: T. Sloat Biological Consulting, Inc., Box 125, McArthur, CA 96056.6Present address: Natural Resource Management & Science, Golden Gate National Recreation Area, Building 201, Fort Mason, San Francisco, CA 94123.

299

species (Uhler 1944, Weller 1994) or it mayenhance the abundance of rare indigenousspecies (Pendergrass et al. 1999). Although firemay be a natural event in some wetlands (e.g.,Willard and Wakimoto 1995) and is commonlyused to manage wetlands (reviewed by Kozlow-ski and Ahlgren 1974, Lyon and Stickney 1976,Wright and Bailey 1982, Kantrud 1986, Payne1992, Weller 1994), few studies have quanti-fied the direct effects of burning on individualplant species in wetlands (e.g., Smith andKadlec 1985a).

Herein we document the effects of pre-scribed fall burning on plant species diversity,species richness, and on individual species ina wet meadow plant community in northeast-ern California that is managed primarily formigrating arctic-nesting geese. Plant commu-nities in the Great Basin floristic region ofnorthern California (Raven 1988) are generallypoorly described, and little is known about theeffects of disturbances, such as burning, onthe dominant plant species. Using a controlledfield experiment, we tested the following hypo-theses: (1) species diversity and richness ofwetland plant communities increase after adisturbance such as fire; (2) the proportion ofnative versus introduced wetland plant speciesincreases after a natural physical disturbance,such as fire; and (3) burning enhances the useof the wetland plant community by wild geese.

Although our field experiment was designedto determine the effects of prescribed fall burn-ing on the plant community and use of theplants by geese during spring, a statistical com-parison of yearly patterns of change in bothburned and unburned plots enabled us to inves-tigate how the effects of prescribed burningon plant species are influenced by interactionswith other abiotic factors, primarily moistureand flooding regimes, and salinity-alkalinityrelationships. We know of no other study thatattempts to quantify the relative importance ofprescribed burning compared to other impor-tant physical factors such as flooding in ex-plaining annual floristic changes in a wetlandplant community.

STUDY AREA

This study was conducted in the northernportion of Fall River Valley, Shasta County,California (Fig. 1). The Fall River Valley is 1 ofmany valleys on the Modoc Plateau in the

Intermountain Region of California and lies atthe extreme western edge of the Great Basinfloristic region (Raven 1988). The northern por-tion of Fall River Valley is a complexly faultedgraben that was occupied by a large Pleisto-cene lake. Deposits from this lake form muchof the light-colored clay, silt, and sandy-silt soilin the valley. Annual precipitation averagesabout 30 cm, with moderately deep snows inthe winter, some spring and fall rains, and rel-atively dry summers (Raven 1988).

The study area was located on a peninsulaat 1009 m between the Tule and Little Tulerivers (Fig. 1). There, Pleistocene lacustrinedeposits are overlain by approximately 1 m ofmore recent basin deposits. Soils on the penin-sula are 85% Pastolla muck (0%–1% slope;classified as medial over clayey, mesic, MollicAndaquepts) and 15% contrasting inclusion ofWhipple soils and organic soils in low positions(Ferrari 1994). The Pastolla muck soils havelow permeability, are poorly drained, and havea high available water capacity. Runoff isponded, and the water table is high and main-tained by flow from springs. In most years, thepeninsula has standing water during late winterand spring, but not during summer and fall.

The seasonally inundated wet meadow onthe peninsula is separated from the rivers byearthen levees that border the peninsula. UntilOctober 1988, the low-lying wet meadow waspartially flooded each spring and then grazedby cattle during summer and fall. Since 1989,the peninsula has been owned and managedby the California Department of Parks andRecreation principally as a feeding and restingsite for migrating geese in the spring. Manage-ment by state park personnel has involvedpartially flooding the study area during earlyspring and prohibiting livestock grazing.Reduced use of the area by geese followingexclosure of livestock led us to initiate thisstudy of prescribed burning and its effect onplant communities and use by migrating geese.

METHODS

Precipitation, Temperature, and Water Level

Monthly precipitation and temperature datawere obtained from a weather station that wasoperated by the California Irrigation Manage-ment District (California Department of WaterResources, Sacramento) about 5 km from the

300 WESTERN NORTH AMERICAN NATURALIST [Volume 67

study area. During spring 1991 and 1992, aspart of the regular management program, Cal-ifornia Department of Parks and Recreationpersonnel flooded portions of the study area tosimulate the seasonal flooding that would occurin the absence of levees after spring rains andincreased flows caused by snowmelt in thesurrounding mountains. To obtain an indicatorof yearly differences in flooding extent, wevisually estimated the proportion of each veg-etation zone on the study area that was cov-ered by standing water in early March andagain in early April in both 1991 and 1992.

Field Experiment

VEGETATION MONITORING.—An inventory ofplant species on the peninsula was conductedon 15 August 1989 prior to prescribed burn-ing. Native species, such as saltgrass (Distich-lis spicata) and foxtail barley (Hordeum juba-

tum), and introduced species such as swamptimothy (Crypsis shoenoides), quackgrass (Ely-trigia repens), and canary grass (Phalaris arun-dinaceae) were dominant on the peninsula(Table 1). The survey revealed obvious zona-tion of the plant community as is commonlyobserved in seasonally flooded freshwater wet-lands with microtopographical elevation changes(Kadlec and Smith 1989, Weller 1994). For pur-poses of vegetation sampling and analysis, wecategorized the vegetation into 3 zones basedon the most conspicuous species. (1) Crypsiszone: the east side of the peninsula was domi-nated by Crypsis shoenoides with Distichlisspicata to a lesser extent (Fig. 1). Plants on theeast side of the peninsula must tolerate thelongest duration of flooding and the wettestsoils. (2) Distichlis zone: on slightly higher,drier ground to the west, D. spicata formednearly a monoculture. (3) Elytrigia zone: on

2007] EFFECTS OF BURNING ON WETLAND PLANTS AND GRAZING GEESE 301

Fig. 1. Map of study area, located on a peninsula in Fall River Valley, Shasta County, California, showing the orienta-tion of the 4 burned and 4 unburned experimental blocks.

302 WESTERN NORTH AMERICAN NATURALIST [Volume 67

TABLE 1. Plant species (scientific and common names) on the peninsula study area in Fall River Valley, Shasta County,California. Surveys were conducted on 15 August 1989 and in early September 1990–1992. Nomenclature follows Hick-man (1993). Absence in the Crypsis (C), Distichlis (D) and Elytrigia (E) zones is indicated by a dash. Presence in theCrypsis, Distichlis, and Elytrigia zones is indicated by an “H” if relative abundance in any block was >5%, by an “M” ifrelative abundance in any block was at most 2%–5%, and by an “L” if relative abundance in any block was always <2%.Status indicates whether the species is native (N) or introduced (I).

Zone______________Scientific name Acronym Common name C D E Status

Euphorbiaceae Euphorbia spp. EUSP spurge H M — N

AlismataceaeSagittaria cuneata E. Sheldon arrowhead — — — N

JuncaceaeJuncus balticus Willd. JUBA rush M L L N

CyperaceaeEleocharis macrostachya Britton ELPA spikerush H M M NScirpus pungens Vahl common three square — — — NScirpus maritimus L. var. plaudosus

(Nelson) Kük SCMA alkali bulrush M L — NPoaceae

Agropyron desertorum (Fischer) Schultes crested wheatgrass — — — IAgrostis gigantea Roth OR stolonifera L. redtop — — — IBromus inermis Leysser smooth brome — — — IBromus secalinus L. chess or cheat — — — IBromus tectorum L. cheatgrass — — — ICrypsis shoenoides (L.) Lam. CRSC swamp timothy H H H IDistichlis spicata (L.) E. Greene var. stricta

(Torrey) Beetle DISP saltgrass H H H NEchinochloa crus-galii (L.) P. Beauv. watergrass — — — NElymus x macounii Vassey Macoun’s wildrye — — — NElymus trachycaulus (Link) Shinn. bearded wheatgrass — — — NElytrigia pontica (Podp.) Holub tall wheatgrass — — — IElytrigia repens (L.) Nevski AGRE quackgrass — L H IHordeum jubatum L. HOJU foxtail barley H H H NLeymus cinereus (Schribner &Merr.) A. Löve Great Basin wildrye — — — NPanicum capillare L. PACA panic grass H H H NPhalaris arundinacea L. PHAR reed canarygrass M M H IPhleum pratense L. timothy — — — IPoa sp. bluegrass — — —Polypogon monspeliensis (L.) Desf. POMO rabbitfoot grass — L L I

BoraginaceaeHeliotropium curassavicum L. HECU heliotrope L L — N

ChenopodiaceaeChenopodium album L. CHAL lamb’s quarters H H M I

AsteraceaeBidens cernua L. bur marigold — — — NLactuca serriola L. LASE prickly lettuce — L H I

ConvolvulaceaeConvolvulus sp. morning glory — — —

FabaceaeLotus corniculatus L. birds-foot trefoil — — — IMedicago lupulina L. black medick — — — ITrifolium sp. clover — — —

PolygonaceaePolygonum douglasii E. Greene PODO smartweed H L — IRumex crispus L. curly dock — — — I

RosaceaePotentilla anserina L. var. anserina POAN silverweed H H M N

the higher, drier ground further to the west,H. jubatum was interspersed with E. repensand with dense low-lying D. spicata.

Plant relative abundance was estimated inearly September 1990–1992 using a point-inter-cept method (Mueller-Dombois and Ellenberg1974). Points were arranged every 2.7 m along2 randomly selected transects in each of 8 ex-perimental blocks (see below). Transects wereparallel and ran the length of each block(approximately 460 m). The same blocks wereused across years, but in each year we estab-lished a new set of transects; thus, points wereindependently established within blocks acrossyears. At each point, a sharpened rod (2 mmdiameter) was dropped vertically, and speciesof the plant hit by the rod was recorded. Weused a ruler to measure vegetation heightevery 10.8 m along the same transects. Wealso measured vegetation height the day afterthe 2 prescribed burns.

BURNING TREATMENT AND EXPERIMENTAL

DESIGN.—We conducted prescribed burningon 3 December 1990 and on 25 November1991. Burning was timed so that plants weresenescent and the residual vegetation was rel-atively dry. Four burned and 4 unburned blockswere alternately arranged side by side on thepeninsula (Fig. 1). Each block was rectangular(50 × 460 m) and averaged 2.3 ha (range 1.9–2.7 ha). The experimental blocks traversed themoisture and vegetation gradients that werecorrelated with microtopographical elevationchanges (generally lower to the east; Fig. 1).We used this experimental design, associatedmeasurements of plant relative abundance, andthe statistical analysis described below to deter-mine the relative importance of burning com-pared to other abiotic factors such as moistureand salinity-alkalinity gradients.

USE OF EXPERIMENTAL BLOCKS BY GEESE.—We monitored use of the experimental blocksby 2 species of herbivorous waterfowl (Cack-ling Goose, Branta canadensis minima Ridg-way, and Pacific Greater White-fronted Goose,Anser albifrons frontalis Baird) from dawn untildusk on 67 days between 15 February and 28April 1992. When we observed geese, we usedscan sampling (Altmann 1974) conducted every20 minutes to record the number and behav-ior (feeding or not feeding) of each individualon burned and unburned blocks. All observa-tions were recorded using a 20X–60X spotting

scope from a blind located on the levee justeast of the experimental blocks (Fig. 1).

Statistical Analyses

We used repeated measures ANOVA toevaluate annual changes in species diversity,species richness (number of species), and theproportion of native versus introduced plantspecies in burned and unburned blocks withineach vegetation zone. We used Simpson’s indexof species diversity,

D = (∑ Pi2)–1

where Pi is the proportion of total hits along 2transects for species i and the summation isacross all plant species (Simpson 1949). Therepeated variable was block (resampled eachyear), and the crossed variable was vegetationzone.

We used ordination and gradient analysis,specifically correspondence analysis (indirectgradient) and canonical correspondence analy-sis (direct gradient; CANOCO 1989, Micro-computer Power, Cornell University, Ithaca,NY), and multiway contingency table analysis(Biomedical Computer Programs P series;BMDP 1992) to evaluate annual changes inrelative abundance of plant species and howburning interacted with these annual changes.The total number of hits per block for eachplant species was used as the dependent vari-able, which emphasizes proportions (i.e., rela-tive abundance) of each species. The use of cor-respondence and canonical correspondenceanalyses is well established in studies such asours (ter Braak and Prentice 1988, Palmer1993). To preserve sufficient statistical power,we used only the 8 most common species inthe contingency table analysis. For CANOCOanalyses, we included only the 16 most com-mon species (Table 1). We verified that all nec-essary assumptions of correspondence andCANOCO analyses were satisfied (Zar 1999).

Effects of burning were detected in themultiway contingency tables as significant inter-actions between treatment (T; burned or un-burned) and plant species (S), vegetation zone(Z), or year (Y). We present results on the 5most common species for which we had themost confidence in interpreting the tableresults. We included vegetation zone (3 cate-gories: Crypsis, Distichlis, Elytrigia) as an in-dependent variable in the model because our

2007] EFFECTS OF BURNING ON WETLAND PLANTS AND GRAZING GEESE 303

subjective observations and the ordinationanalysis clearly identified a moisture-relatedgradient associated with these zones. Includ-ing vegetation zone in the model enabled us todetect interactions between the effects of treat-ment and vegetation zone on relative densityof a plant species.

As per multiway contingency table notation,if there was no interaction between 2 variables(e.g., treatment and vegetation zone) we de-noted it by separating their symbols with acomma (T,Z), whereas if there was an interac-tion we denoted it by a lack of a comma (TZ).In multiway contingency table analysis, dataare “fit” to certain models that differ in com-plexity. The saturated model, by definition,always fits the data best (P = 1.0). The goal isto find the simplest model that fits (P > 0.05)the data but that is not significantly differentfrom more complex models that also fit thedata (Fienberg 1970, Jenkins 1975), followingthe principle of parsimony. Once the simplestmodel was determined, we used the methodsof Toft (1984a, 1984b) to determine the exactsource of a particular significant interaction.In short, this method involves fitting an appro-priate null model or models to the data andthen examining calculated standardized devi-ates (i.e., dimensionless, weighted deviationsfrom expected values). The appropriate nullmodel is the same as the simplest model exceptthat the 1 interaction of interest is removed.

We used the goodness-of-fit test with Yates’correction for continuity (Zar 1999) to evaluateuse of burned and unburned experimentalblocks by foraging geese.

RESULTS

Precipitation, Temperature, and Water Levels

Growing season (March–September) pre-cipitation was less in 1991 than in 1990 and1992 (Fig. 2A). In 1990, precipitation wasgreatest during March and especially high inMay (Fig. 2A). Mean high and low tempera-tures for a given month were similar in 1990,1991, and 1992 (Fig. 2B).

Flooding during spring was more extensivein 1991 than in 1992. In early March 1991,standing water covered 100% of both theCrypsis and Distichlis zones and 20% of theElytrigia zone, whereas in 1992 standing watercovered 100% of only the Crypsis zone, 50% of

the Distichlis zone, and none of the Elytrigiazone. By early April 1991, standing water cov-ered 65% of the Crypsis zone and none of theDistichlis or Elytrigia zones, whereas in 1992there was no standing water on the study area.

Zonation of Vegetation

Vegetation on the study area was dominatedby grasses, sedges, and rushes (Table 1). In1990, prior to any burning, the 3 vegetationzones that were identified a priori in the studydesign were confirmed by the indirect gradi-ent analysis (Fig. 3): (1) Elytrigia zone whereE. repens was associated with H. jubatum, P.arundinaceae, and Lactuca seriola; (2) Distich-lis zone where D. spicata was the predominantspecies; and (3) Crypsis zone where C. shoe-noides was associated with Panicum capillare,Chenopodium album, and other less abundantspecies. In addition, each sampling point in anexperimental block was assigned to a vegeta-tion zone. This resulted in 8 sites (1 per exper-imental block) for each vegetation zone thatwere identified a priori in the study design.The 8 sites designated to each vegetation zonewere distinctly clustered on the ordination nearthe plant species associated with that vegeta-tion zone (Fig. 3), demonstrating that the veg-etation zones were unambiguous and not arbi-trary.

The 1st axis of the unconstrained ordina-tion represented the obvious moisture gradi-ent on the study area, from wet (Crypsis zone)with positive values on axis 1, to intermediate(Distichlis zone), to dry (Elytrigia zone) withnegative values on axis 1 (Fig. 3). By defini-tion, axis 1 explains the most variation in occur-rence of species in the ordination; in 1990 itexplained 41% of the variation (Table 2A). The2nd axis explained an additional 25% of thevariation and, given the position of D. spicata(saltgrass) on 1 end of the continuum, this axisappeared to represent a salinity-alkalinity gra-dient. Axes 3 and 4 represented residual vari-ation.

Efficacy of Burning

Burning in the fall effectively reduced thestanding biomass of vegetation as indicated byvegetation height before (measured on 8 Sep-tember 1990 and 31 August 1991) and justafter (measured on 3 December 1990 and 25November 1991) each burn (repeated measuresANOVA, year effect: F1, 12 = 0.8, P = 0.386;

304 WESTERN NORTH AMERICAN NATURALIST [Volume 67

treatment effect: F1, 12 = 24.1, P < 0.0001).Vegetation height in burned plots was reducedfrom 25.0 ± 1.7 cm to 8.2 ± 0.6 cm in 1990,and from 31.7 ± 1.0 cm to 5.3 ± 0.7 cm in1991, while vegetation height in unburnedplots changed relatively less (24.3 ± 1.4 cm to19.2 ± 1.4 cm in 1990, and 23.0 ± 1.5 cm to19.6 ± 0.6 cm in 1991). The prescribed burnin fall 1991 reduced residual vegetation morethan the burn in fall 1990 (year × time effect:F1, 12 = 5.4, P = 0.04; treatment × time: F1, 12= 104.2, P < 0.0001). Burning was uniformacross the blocks, as indicated by the relative-ly small range in vegetation height after burn-ing (7.0–9.8 cm in 1990, 3.6–7.0 cm in 1991).

Effects of Burning on Attributes of the Plant Community

Although more species occurred in the Dis-tichlis zone (Fig. 4A; zone effect: F2, 18 = 9.7,P = 0.001), the dominance of 1 species, D. spi-cata, resulted in the Distichlis zone having thelowest diversity index for all zones (Fig. 4B).Species diversity was highest in the Crypsiszone (Fig. 4B; zone effect: F2, 18 = 16.3, P <0.001), reflecting more equitable relative abun-dance of species there. Both richness anddiversity of species were highest in 1991 (yeareffect, richness: F2, 36 = 26.3, P < 0.0001; yeareffect, diversity: F2, 36 = 29.6; P < 0.0001), al-though the pattern of annual change in species

2007] EFFECTS OF BURNING ON WETLAND PLANTS AND GRAZING GEESE 305

Fig. 2. Total monthly precipitation (cm) and monthly average high (solid line) and low (dashed line) temperature (°C)during 1990, 1991, and 1992 in Fall River Valley, Shasta County, California.

Ave

rag

e m

on

thly

tem

per

atu

re (

°° C)

Mo

nth

ly p

reci

pit

atio

n (

cm)

richness and diversity depended on the vege-tation zone (year × zone interaction, richness:F4, 36 = 4.2; P = 0.007; year × zone interaction,diversity: F4, 36 = 9.5, P < 0.0001). About50% more species occurred in all 3 vegetationzones in 1991 than in 1990 (Fig. 4A). Higherspecies richness was maintained in the Cryp-sis and Distichlis zones in 1992, but speciesrichness declined in the Elytrigia zone in 1992.In 1991, species diversity increased by about50% in the Crypsis and Distichlis zones butincreased only slightly in the Elytrigia zone(Fig. 4B). In 1992, species diversity declinedin all 3 vegetation zones.

Burning had no significant effect on speciesrichness (treatment effect: F1, 18 = 0.1, P =0.759; year × treatment interaction: F2, 36 =1.1, P = 0.358; year × treatment × zone inter-action: F4, 36 = 0.5; P = 0.767; Fig. 4A) or onthe proportion of native versus introduced plantspecies (treatment effect: F1, 18 = 0.6, P =0.454; year × treatment interaction: F2, 36 =

0.4, P = 0.665; year × treatment × zone inter-action: F4, 36 = 1.4, P = 0.243). Burning had asignificant effect on species diversity (Fig. 4B),although the increase in species diversity asso-ciated with burning was more apparent in1991 than in 1992 (treatment effect: F1, 18 =0.8, P = 0.377; year × treatment interaction:F2, 36 = 4.3, P = 0.02; year × treatment ×zone interaction: F4, 36 = 1.5, P = 0.237).

To examine how much variation was ex-plained by the effects of burning, we con-strained the ordination with 1 environmentalvariable, the burn treatment, using canonicalcorrespondence analysis. In this direct gradientanalysis, axis 1 discriminated between burnedand unburned sites (Fig. 5, Table 2B). As ex-pected, in 1990 prior to the prescribed burn-ing, axis 1 explained little (0.6%) of the varia-tion in plant species (Table 2B), and mostspecies were close to 0 on axis 1 (Fig. 5A). Inthis direct gradient analysis, only axis 1 wasconstrained by us to show the effects of the

306 WESTERN NORTH AMERICAN NATURALIST [Volume 67

Fig. 3. Ordination of plant species in 1990, prior to prescribed burning, by correspondence analysis. In this analysisspecies or site positions are unconstrained by data on environmental variables. Scores on the 2 axes for plant species arefilled circles and scores for the 8 sites in each zone are open squares. Key species for each of the 3 identifiable vegeta-tion zones are in boldface type.

burn treatment. Axes 2 to 4 were uncon-strained and, as before, were ordered by thedegree to which they explained variation inplant species abundance. Thus, axis 2 repre-sented the moisture gradient (compare withaxis 1 in Fig. 3); axis 3 represented the pro-posed salinity-alkalinity gradient (compare withaxis 2 in Fig. 3); and axis 4 contained the resid-ual variation (Table 2B).

Plant species increasingly diverged alongaxis 1 after 1 year (Fig. 5B) and 2 years (Fig. 5C)of burning, suggesting that some species wereinhibited (positive values on axis 1) and otherswere promoted (negative values on axis 1) byburning (compare Figs. 5 and 6). After eachyear of burning, more variation in plant species

2007] EFFECTS OF BURNING ON WETLAND PLANTS AND GRAZING GEESE 307

Fig. 4. Plant species richness (A) and diversity (B) inburned and unburned experimental blocks within 3 vege-tation zones during 1990–1992 in Fall River Valley, ShastaCounty, California. Species richness and diversity of plantsin 1990 were measured prior to prescribed burning.

A

B

C

Fig. 5. A, Ordination of plant species in 1990, prior toburning. Axis 1 is constrained by burn treatment; axis 2 isunconstrained and represents the moisture gradient. B,Ordination of plant species in 1991, after 1 burn treat-ment on 3 December 1990. Axis 1 is constrained by burntreatment; axis 2 is unconstrained and represents themoisture gradient. C, Ordination of plant species in 1992,after a 2nd burn treatment on 25 November 1992. Axis 1is constrained by burn treatment (see text); axis 2 isunconstrained and represents the moisture gradient.Four-letter acronyms for each plant species are defined inTable 1. Key species for each of the 3 identifiable vegeta-tion zones are in boldface type.

ELPA

was explained by the effect of burning, in-creasing to 5% in 1991 and to 10% in 1992;and the species-burn treatment correlationincreased notably (Table 2B). However, themoisture gradient represented by axis 2 re-mained the most important environmental fac-tor even after 1 and 2 years of burning (Fig. 5).This ordination analysis of species-specificresponses also suggests that the effect of burn-ing depended on vegetation zone (represent-ing the moisture gradient), in that the speciesdiverged in the 2-dimensional ordinationalong a diagonal (compare Figs. 5A and 5C).

Effect of Burning on Individual Plant Species

The relative abundance of plant specieswithin each of the 3 vegetation zones changedacross years in both burned and unburnedblocks (Fig. 6). We assessed the relationshipbetween the species-specific effects of burn-ing and the moisture gradient using multiwaycontingency table analysis.

The effects of burning on abundance of the8 most common plant species differed amongspecies, and interacted with vegetation zone(reflecting the moisture gradient) and year(Fig. 6). The 4-dimensional model (dependentvariable = number of hits * burn treatment[T] * species [S] * zone [Z] * year [Y]) was theonly model that fit the data (χ2 [likelihoodratio chi-square] = 0.0, P = 1.0). However, theχ2 value for fitting the next-less-complex modelof all possible 3-way interactions (model:(YTZ,STZ,SYZ,SYT), χ2 = 74.5, df = 21, P <0.00001) was relatively small (χ2 values for

models containing only the much simpler 2-and 1-dimensional effects were greater than4500) suggesting that the additional informa-tion provided by the 4th-order interaction wasnot great.

Given that the 4-way interaction was rela-tively uninformative, we analyzed key-compo-nent 3-way models, decomposing the 4-waymodel along certain dimensions. We first ana-lyzed years separately while including thespecies effect [S]. As expected, the [STZ] modelwas the simplest model that fit the data in allyears. Prior to the prescribed burn in 1990,the treatment effect [T] alone was not signifi-cant (χ2 = 1.96, P = 0.16), nor was the spe-cies-treatment interaction (χ2 = 2.45, P =0.94). The [SZ] interaction was the strongesteffect (χ2 = 804.2, P << 0.0000), which meantthat the zones differed in species composition.These results supported the study design (i.e.,no treatment effect overall before the treat-ments began) and the ordination results above(Fig. 3). In 1990, the 3-way [STZ] model wasthe simplest, best-fit model because of a slighttreatment-zone interaction (χ2 = 14.7, P =0.0007). Thus, there was a pretreatment differ-ence in plant density in the blocks designatedfor burning versus the control blocks thatdepended on the zone. This pretreatment biaswas also evident in the ordination and will bediscussed below under the individual speciesthat contributed to it. Finally, by 1992 thetreatment effect was much stronger and statis-tically significant (χ2 = 98.5, P <0.0000). Thus,burning had a measurable effect on the plantcommunity in all zones.

308 WESTERN NORTH AMERICAN NATURALIST [Volume 67

TABLE 2. Summary of indirect (A) and direct (B) gradient analyses. The sum of eigenvalues, the species-burn treatmentcorrelation, and the cumulative percentage of variation in plant species explained by each axis provide different mea-sures of the explanatory power of the ordination. In the indirect gradient analysis, in which all axes are unconstrained,axis 1 represents the moisture gradient and axis 2 represents a salinity-alkalinity gradient; axes 3 and 4 measure residualvariation. In the direct gradient analysis, axis 1 is constrained by burn treatment and the remaining axes are uncon-strained; axis 2 represents the moisture gradient, axis 3 represents a salinity-alkalinity gradient, and axis 4 measuresresidual variation.

Cumulative percent variation____________________________________Year Sum of eigenvalues Species–burn correlation Axis 1 Axis 2 Axis 3 Axis 4

A. Indirect gradient analysis (unconstrained)1990 0.912 — 41.4 66.1 77.9 85.31991 0.796 — 38.8 68.9 78.3 84.41992 0.841 — 39.4 65.9 77.3 83.8

B. Direct gradient analysis (constrained by burn treatment)1990 0.912 0.279 0.6 42.0 66.7 78.51991 0.794 0.595 4.9 43.9 73.0 79.71992 0.830 0.630 9.9 45.8 72.4 79.5

Next we analyzed the 3-way tables by spe-cies (Table 3), interpreting and expanding onpatterns evident in Fig. 6. To determine howthe effect of burning differed by vegetationzone and year, we examined departures from 2null models: (1) departures from the null model[TY,ZY] indicate how the effect of burning dif-fered by vegetation zone (i.e, [TZ] effect miss-ing; Table 4), whereas (2) departures from thenull model [TZ,ZY] indicate how the effect ofburning differed by year (i.e., [TY] effect miss-ing; Table 5). We interpreted these results, byspecies, as follows:

DISTICHLIS SPICATA.—D. spicata was com-mon throughout the study area (Fig. 6), but itsrelative abundance was greatest in the Distich-lis zone (by definition), which was intermediateon the moisture gradient (Fig. 5). Before the

burn treatment in 1990, D. spicata was moreabundant than expected in the to-be-burnedsites in the Distichlis zone (Fig. 6, Table 5). Afterthe initial burn treatment in 1991, D. spicatawas less abundant than expected in the burnedblocks than it was in the unburned blocks (Fig.6, Table 5) when spring flooding was exten-sive. The negative effect of burning on D. spi-cata in the Distichlis zone in 1991 was not asobvious after the 2nd burning in 1992 (Fig. 6,Table 5). In 1991, the abundance of D. spicatashowed the strongest differences among zones(Table 4), probably indicating the sensitivity ofthis species to the joint effects of burning andthe flooding regimen that year.

HORDEUM JUBATUM.—At the start of the studyin 1990, H. jubatum was rare in all but theElytrigia zone, where it was relatively more

2007] EFFECTS OF BURNING ON WETLAND PLANTS AND GRAZING GEESE 309

Fig. 6. Relative abundance of all plant species in burned (dark-shaded bars) and unburned (unshaded bars) experi-mental blocks within 3 vegetation zones during 1990–1992 in Fall River Valley, Shasta County, California. Relative abun-dance of plants in 1990 was measured prior to prescribed burning.

310 WESTERN NORTH AMERICAN NATURALIST [Volume 67

TAB

LE

3. A

ll po

ssib

le p

artia

l ass

ocia

tions

from

fitt

ing

the

fully

sat

urat

ed 3

-fac

tor

mod

el s

epar

atel

y fo

r ea

ch o

f 5 p

lant

spe

cies

in u

nbur

ned

and

burn

ed p

lots

(n=

4) i

n Fa

ll R

iver

Val

-le

y, C

alifo

rnia

. S =

pla

nt s

peci

es (s

ee d

escr

iptio

n in

Res

ults

); Y

= y

ear

(199

0, 1

991,

199

2); T

= tr

eatm

ent (

burn

ed o

r un

burn

ed);

Z =

veg

etat

ion

zone

(Cry

psis

, Dis

tichl

is, E

lytr

igia

).

Dis

tichl

isH

orde

umC

ryps

isPh

alar

isE

lytr

igia

____

____

____

____

____

___

____

____

____

____

____

____

____

____

____

____

____

____

____

____

___

____

____

____

____

_E

ffect

dfχ2

P-va

lue

χ2P-

valu

eχ2

P-va

lue

χ2P-

valu

eχ2

P-va

lue

T1

1.74

0.18

7434

0.8

0.00

000.

10.

7131

34.2

0.00

005.

40.

0199

Z2

4511

.00.

0000

631.

50.

0000

0.3

0.59

5339

.30.

0000

153.

10.

0000

Y2

484.

40.

0000

501.

10.

0000

4.1

0.12

7922

.90.

0000

45.1

0.00

00T

Z2

28.4

0.00

0040

.30.

0000

0.6

0.45

560.

90.

3444

2.1

0.15

03T

Y2

44.6

0.00

0066

.80.

0000

15.9

0.00

0411

.10.

0039

22.3

0.00

00YZ

4 6.

20.

1819

241.

00.

0000

298.

90.

0000

0.01

0.99

5310

.10.

0065

TZ

Y4

15.3

0.00

4033

.80.

0000

16.5

0.00

030.

60.

7564

2.1

0.35

72

TA

BL

E4.

Env

iron

men

tal

vari

atio

n in

the

effe

cts

of b

urni

ng o

n th

e 5

mos

t co

mm

on s

peci

es i

n th

e w

etla

nd c

omm

unit

y in

Fal

l R

iver

Val

ley,

Cal

iforn

ia.

Stan

dard

ized

dev

iate

s[(o

bser

ved

– ex

pect

ed) ÷

√exp

ecte

d] f

rom

a m

ultiw

ay c

ontin

genc

y ta

ble

anal

ysis

tha

t te

sts

for

the

[TZ

] effe

ct (i

.e.,

null

mod

el [T

Y, Z

Y]) i

n bu

rned

and

unb

urne

d pl

ots

(n=

4).

Lar

gest

anda

rdiz

ed d

evia

tes

indi

cate

str

ong

effe

cts

of th

e 1

inte

ract

ion

that

was

rem

oved

, and

the

sign

(+ o

r –)

of t

he d

evia

te in

dica

tes

whe

ther

the

obse

rved

val

ues

are

grea

ter

than

or

less

than

the

expe

cted

val

ues

from

the

null

mod

el. T

wo

plan

t spe

cies

(Pha

lari

s ar

undi

nace

aan

d E

lytr

igia

rep

ens)

wer

e ab

sent

from

the

Cry

psis

vege

tatio

n zo

ne.

Dis

tichl

is

Hor

deum

Cry

psis

Phal

aris

Ely

trig

ia__

____

____

____

____

____

____

____

____

____

____

____

____

____

____

____

____

____

____

____

____

____

____

____

____

__Ye

arVe

geta

tion

zone

unbu

rned

burn

edun

burn

edbu

rned

unbu

rned

burn

edun

burn

edbu

rned

unbu

rned

burn

ed

1990

Cry

psis

–0.5

+0.

50

0–1

.4+

1.3

——

——

Dis

tichl

is+

0.5

–0.5

+3.

2–3

.1+

1.0

–1.0

–0.1

+0.

1+

1.3

–1.1

Ely

trig

ia–0

.7+

0.7

–1.8

+1.

8+

2.1

–2.0

+0.

10

–0.4

+0.

419

91C

ryps

is–3

.4+

3.8

–4.4

+2.

9–2

.0+

2.0

——

——

Dis

tichl

is+

1.8

–2.0

+1.

9–1

.3+

1.6

–1.6

+0.

8–0

.5+

0.6

–0.6

Ely

trig

ia–1

.4+

1.6

+0.

4–0

.2+

1.5

–1.5

–0.5

+0.

3–0

.2+

0.2

1992

Cry

psis

–1.3

+1.

3–1

.0+

0.5

–2.8

+3.

3—

——

—D

istic

hlis

+0.

3–0

.3–0

.1+

0.1

+2.

9–3

.4+

0.4

–0.2

–0.1

0E

lytr

igia

+0.

4–0

.4+

0.9

–0.4

+1.

9–2

.2–0

.2+

0.1

00

abundant in the to-be-burned blocks (Fig. 6,Table 4). After the burn treatments, H. juba-tum was more abundant than expected in theburned blocks than it was in the unburnedblocks in the Crypsis zone in 1991 and 1992.Moreover its abundance in the Elytrigia zoneand especially in the Distichlis zone increasednotably in the burned blocks in 1992 (Fig. 6,Tables 4, 5). Thus, burning generally enhancedthe abundance of H. jubatum, although thestrong [YZ] interaction (Table 3) indicated thatthe strength of the burning effect dependedon the vegetation zone and year.

CRYPSIS SHOENOIDES.—This species was rel-atively rare in all but the Crypsis zone (Fig. 6),which was wettest on the moisture gradient.Before the burn treatment in 1990, C. shoe-noides was slightly more abundant than ex-pected in the to-be-burned sites in the Crypsiszone, and less abundant in the to-be-burnedblocks in the Distichlis zone and especially inthe Elytrigia zone (Fig. 6, Table 4). Crypsisshoenoides was suppressed by burning in thedrier Distichlis and Elytrigia zones, especiallyin 1992, although burning did not suppress C.shoenoides as much in the Crypsis zone (Fig.6, Tables 3, 4, 5). Thus, the abundance of C.shoenoides was generally suppressed by burn-ing, although the strong [YZ] interaction (Table3) indicated that the strength of the burningeffect depended on the vegetation zone andyear.

ELYTRIGIA REPENS AND PHALARIS ARUNDINA-CEAE.—These species were relatively rare over-all, and absent from the Crypsis zone (Fig. 6).Before the burn treatment in 1990, P. arundi-naceae was less abundant in the to-be-burnedsites in the Distichlis and Elytrigia zones, whileE. repens was less abundant in the to-be-burned sites in the Distichlis zone, but not theElytrigia zone (Fig. 6, Tables 4, 5). After the1st burn treatment, P. arundinaceae and espe-cially E. repens were less abundant than ex-pected in the burned blocks than they were inthe unburned blocks in 1991 (Fig. 6, Tables 4and 5) when spring flooding was more exten-sive. In 1992, both E. repens and P. arundina-ceae were more abundant than expected in theburned than in the unburned blocks in theDistichlis and Elytrigia zones (Fig. 6, Table 5).For both E. repens and P. arundinaceae, thetreatment-by-year interactions [TY] were thestrongest of the 3 possible 2-way interactions(Table 3).

2007] EFFECTS OF BURNING ON WETLAND PLANTS AND GRAZING GEESE 311

TAB

LE

5. Y

earl

y va

riat

ion

in t

he e

ffect

s of

bur

ning

on

the

5 m

ost

com

mon

spe

cies

in

the

wet

land

com

mun

ity i

n Fa

ll R

iver

Val

ley,

Cal

iforn

ia.

Stan

dard

ized

dev

iate

s [(o

bser

ved

–ex

pect

ed) ÷

√exp

ecte

d] fr

om a

mul

tiway

con

tinge

ncy

tabl

e an

alys

is t

hat

test

s fo

r th

e [T

Y] e

ffect

(i.e

., nu

ll m

odel

[TZ

,ZY]

) in

unbu

rned

and

bur

ned

plot

s (n

= 4

). L

arge

sta

ndar

dize

dde

viat

es i

ndic

ate

stro

ng e

ffect

s of

the

1 i

nter

actio

n th

at w

as r

emov

ed, a

nd t

he s

ign

(+ o

r –)

of

the

devi

ate

indi

cate

s w

heth

er t

he o

bser

ved

valu

es a

re g

reat

er t

han

or l

ess

than

the

expe

cted

val

ues

from

the

null

mod

el. T

wo

plan

t spe

cies

(Pha

lari

s ar

undi

nace

aan

d E

lytr

igia

rep

ens)

wer

e ab

sent

from

the

Cry

psis

vege

tatio

n zo

ne.

Dis

tichl

isH

orde

umC

ryps

isPh

alar

isE

lytr

igia

____

____

____

____

____

____

____

____

____

____

____

____

____

____

____

____

____

____

____

____

____

____

____

____

____

Year

Vege

tatio

n zo

neun

burn

edbu

rned

unbu

rned

burn

edun

burn

edbu

rned

unbu

rned

burn

edun

burn

edbu

rned

1990

Cry

psis

+0.

9–0

.70

0–0

.2+

0.2

——

——

Dis

tichl

is–1

.0+

1.1

+6.

6–4

.0–0

.9+

1.2

+0.

7–0

.5+

1.1

–1.0

Ely

trig

ia–0

.7+

0.7

+1.

1–0

.7+

0.4

–0.7

+2.

0–1

.3–0

.4+

0.4

1991

Cry

psis

–0.6

+0.

5–0

.8+

0.2

+0.

2–0

.1—

——

—D

istic

hlis

+3.

9–4

.1+

3.3

–2.0

–0.8

+1.

1+

0.6

–0.4

+0.

9–0

.8E

lytr

igia

+0.

6–0

.6+

0.5

–0.3

–0.7

+1.

2+

0.2

–0.1

+1.

7–1

.419

92C

ryps

is–0

.1+

0.1

+1.

2–0

.30

0—

——

—D

istic

hlis

–3.2

+3.

4–4

.1+

2.5

+1.

9–2

.7–1

.1+

0.8

–1.5

+1.

4E

lytr

igia

–0.1

+0.

1–1

.7+

1.1

+0.

6–1

.0–1

.5+

1.0

–2.4

+2.

0

Effect of Burning on Numbers and Behavior of Geese

Cackling Geese were observed using thepeninsula (Fig. 1) on 1 of 67 observation days.On 23 March, 30 Cackling Geese fed for lessthan 30 minutes in the southern tip of thepeninsula and were never close to the experi-mental blocks. White-fronted Geese were ob-served using the peninsula on 10 of 67 obser-vation days. On 4 of the 10 days (1 April, 3April, 10 April, and 17 April), White-frontedGeese were observed using the experimentalblocks. On 10 April, 2 geese were presentfrom 1100 hours to 1130 hours, and on 17April, 6 geese were present from 0740 hoursto 1030 hours. On 1 and 3 April, 15–45 geesewere present on the experimental blocks from0730 hours to 1800 hours; most of this timethe geese were resting on the flooded portionof the blocks. After 1600 hours on both 1 Apriland 3 April, the geese began feeding in theexperimental blocks. During these eveningfeeding periods on 1 April and 3 April, moregeese were observed in burned blocks (19.8and 31.5 geese, respectively) than in unburnedblocks (1.3 and 1.0 geese, respectively; signifi-cant treatment effect on each day, P < 0.001),and geese fed only when they were in burnedblocks (7.8 feeding geese per scan on 1 April,11.0 feeding geese per scan on 3 April; nofeeding geese on either day in unburnedblocks; significant treatment effect on eachday, P < 0.025).

DISCUSSION

Wetland Plant Communities and the Relative Importance of Fire

We found that burning explained, at most,10% of the total variation in plant species. Themoisture and salinity-alkalinity gradientsexplained the majority (>60%) of the totalvariation in plant species. Not surprisingly,management of wetlands typically involvesmanipulating water levels because it so strong-ly influences the plant community (Smith etal. 1989, Weller 1994). It does not follow, how-ever, that prescribed burning has an inconse-quential effect on wetland plant communities.Instead, our results show that the effects of pre-scribed burning, like the effects of many othermanagement activities, are often contingenton interactions with other important ecologi-cal factors. Below we consider interactions

between 3 important ecological factors (burn-ing, moisture, and salinity) as we evaluate the3 hypotheses initially posed in this study.

Effects of Burning on Attributes of the Plant Community:

Does Burning Increase Plant Diversity and Richness, and the Proportion

of Native Plant Species?

Species diversity and species richness ofplant communities that are infrequently burnedtypically peak soon after fire and then declineas the community ages (Whelan 1995, Bondand van Wilgren 1996). In one of the few long-term studies that focused on the effects of firefrequency on diversity and richness of wet-land plant communities, species diversity de-clined with fire frequency (from 2.77 in sitesburned at 20-year intervals to 1.64 in annuallyburned sites) in Spartina wetlands in north-eastern Kansas ( Johnson and Knapp 1995).Most studies of the short-term effects of burn-ing on wetland communities show that burn-ing enhances plant diversity and richness(Schmalzer et al. 1991, Cowie et al. 1992, deSzalay and Resh 1997).

In the wet meadow plant community thatwe studied over 3 years, burning had no effecton species richness, but burning increased plantspecies diversity especially in the 2 wettervegetation zones (Distichlis and Crypsis zones).The increase in plant species diversity was notassociated with an increase in the proportionof native versus introduced plant species.Rather, the increase in plant species diversitywas caused primarily by a decrease in relativeabundance of common native species (e.g., D.spicata) and introduced species (e.g., C. shoe-noides) and an increase in relative abundanceof less common native species (e.g., H. juba-tum, Panicum capillare) and introduced species(e.g., Chenopodium album). Thus, natural dis-turbances such as fire may increase plant spe-cies diversity, but not necessarily the diversityof native plant species.

Burning may initially enhance species rich-ness and diversity in wetlands because it pro-duces bare ground, which provides microhab-itat for seedling recruitment (Van der Valk1986), or because the wetlands are dominatedby perennial rhizomatious species that resproutreadily after fire (Schmalzer et al. 1991). Also,burning may be necessary for the persistence

312 WESTERN NORTH AMERICAN NATURALIST [Volume 67

of rare, native, fugitive species in these sys-tems (Kirkman and Sharitz 1994, Pendergrasset al. 1999). Determining which processes aremost important in structuring wetland plantcommunities that are burned requires anunderstanding of how individual plant speciesrespond to burning.

Effect of Burning on Individual Plant Species

The Clementsian view of an orderly, pre-dictable pattern of succession following distur-bance (see Pickett et al. 1987, Luken 1990,Glenn-Lewin et al. 1992) has been applied topost-fire succession (e.g., Phillips 1934, 1935a,1935b) but has proven generally inadequate,primarily because relative competitive abilityoften poorly predicts observed changes in plantcommunities after fire (Bond and van Wilgren1996). Fire ecologists instead emphasize theinterplay between disturbance frequency, spe-cies-specific mechanisms of persistence dur-ing a disturbance, ability to establish after adisturbance, and the timing of both distur-bance events and key life history variables suchas time to reproductive maturity and life span(Noble and Slatyer 1980, Bond and van Wilgren1996, Menges and Hawkes 1998). Thus, anunderstanding of the patterns of persistence ofindividual plant species is essential for predict-ing temporal changes in plant communitiesafter fire.

In this study, the complexity of the plantcommunity’s response to prescribed burningwas caused by individual species-specific re-sponses to fire that, in turn, depended on site-specific abiotic and biotic conditions. Of the 5perennial plant species that were most abun-dant at our study area, 1 native species (H.jubatum) was consistently more abundant thanexpected following burning, and 1 introducedspecies (C. shoenoides) was consistently lessabundant than expected following burning.Two introduced species (E. repens and P. arun-dinaceae) were less abundant than expectedfollowing burning in 1991, when flooding wasmore extensive, and then more abundant thanexpected following burning in 1992, whenflooding was less extensive. The response ofthe 5th species (D. spicata, native) to burningwas different in each of the 3 vegetation zonesrepresenting the physical moisture gradient.

Without disturbance such as fire, H. juba-tum was rare in all but the Elytrigia zone,

probably because it does not persist in hyper-saline soils (Badger and Ungar 1989, 1991). Ofthe 5 predominant plant species in our studyarea, H. jubatum is the only species that effec-tively invades disturbance-generated bare spaceboth vegetatively and through seed dispersal(Hadley 1970, Payne 1992). It also emergesearly and grows quickly compared to the other4 common species (Payne 1992), although thesetraits may negatively affect its abundance ifearly spring fires coincide with the activegrowth period (Hadley 1970). Johnson andKnapp (1995) found that wetland plant species,which emerged early in the spring and hadrapid shoot growth, increased in relative abun-dance with frequent fire.

The abundance of C. shoenoides was gener-ally suppressed by burning, particularly in thedrier Distichlis and Elytrigia zones, and burn-ing effects were weaker on C. shoenoides inthe Crypsis zone, where this species was mostabundant. A common response to burning issuppression of certain plant species (reviewedby Kirby et al. 1988, Pederson et al. 1989, Payne1992), and this response is often the motiva-tion to burn wetlands that have encroachingwoody vegetation, or to burn dense mono-specific stands of Typha, Scirpus, Cladium, Spar-tina, Phragmites, and other plants that are con-sidered a nuisance when too common (Saleand Wetzel 1983, Payne 1992, Weller 1994).

Both E. repens and P. arundinaceae, whichwere either suppressed or enhanced by burn-ing (depending on flooding regimen), primar-ily invade disturbance-generated bare spacevegetatively (Lyon and Stickney 1976, Payne1992). Like H. jubatum, both E. repens and P.arundinaceae are intolerant of hypersalinesoils (Pederson et al. 1989, Payne 1992), and inour study they were relatively common only inthe drier Elytrigia zone. Our results suggestthat the abundance of both E. repens and P.arundinaceae may be reduced by burningcombined with spring flooding.

D. spicata is a native perennial that rapidlyinvades disturbance-generated bare space vege-tatively (Bertness 1991). It is also quite toler-ant of stressful physical conditions, such ashypersaline soils (Hansen et al. 1976, Skougardand Brotherson 1979, Bertness and Ellison1987, Brotherson 1987) or burial by floatingplant debris (Bertness 1991). However, if flood-ing occurs soon after burning in the fall, stand-ing crop of Distichlis spicata during the next

2007] EFFECTS OF BURNING ON WETLAND PLANTS AND GRAZING GEESE 313

growing season is dramatically decreased (Smithand Kadlec 1985a). If flooding is delayed 2–7weeks after burning in the fall, the depressionof D. spicata is much less extensive (de Szalayand Resh 1997). We found that fall burningreduced D. spicata abundance during the nextgrowing season, especially when spring flood-ing was extensive, although the level of re-sponse was different for each of the 3 vegeta-tion zones.

Does Fall Burning Enhance the Use of Wetlands by Migrating

Geese during Spring?

Prescribed burning of wetlands is used toinhibit invasion of shrubs into graminoid wet-lands (Kushland 1990), to enhance the abun-dance of rare indigenous species (Pendergrasset al. 1999), to improve the quality and quan-tity of available forage for grazing (McAtee etal. 1979a, 1979b, Smith et al. 1984, Schmalzerand Hinkle 1993), and to encourage growth ofpreferred wildlife food for migratory and win-tering waterfowl and shorebirds (Givens 1962,Goodwin 1979, Kadlec and Smith 1989). Insuch systems, burning in the fall or early springfollowed by flooding generally improves habi-tat conditions during the next growing season,whereas burning in summer reduces wetlandplant cover during the summer nesting seasonand reduces habitat quality for waterfowl infall and winter (Martz 1967, Fredrickson andTaylor 1982, Laubhan 1995, Fredrickson andLaubhan 1996).

At our study area, the seasonally floodedwetland is managed primarily for spring migrat-ing waterfowl, especially grazing geese, on theassumption that burning in the fall followedby flooding in the spring enhances the avail-ability of newly growing forage because thisregime reduces residual litter and provides ad-jacent flooded sites for birds while they rest.We found that when geese used the experi-mental blocks for feeding there was a clearpreference for burned compared to unburnedblocks. Thus, fall burning on a larger scalemay provide suitable habitat for grazing geeseduring their spring migration. Because herbi-vores directly influence wetland plant commu-nities (Bakker 1985, Fuller et al. 1985, Bazelyand Jefferies 1986, Foote et al. 1988), burningmay affect the interaction between the herbi-vore and its food supply, although evidence forsuch an interaction between fire and herbi-

vory is currently lacking for wetlands (Tayloret al. 1994, Miller et al. 1997) but not for othersystems (e.g., grasslands [Hobbs et al. 1991]).If more geese had fed in the experimentalblocks during our study, then preferential graz-ing by geese may have affected the wetlandplant community along with burning.

Management Implications

Prescribed burning is an important man-agement tool, especially for ecosystems suchas prairies, scrublands, and wetlands that havefire as part of their natural history. Determin-ing the effect of prescribed burning on suchplant communities is complicated because itseffect is often not simply positive or negative,but is contingent on other important ecologicalfactors (Packard and Mutel 1997, Menges andHawkes 1998). Using an experimental approach,we show that prescribed burning has direct,positive effects on some wetland plant species(e.g., H. jubatum) and direct negative effectson others (e.g., C. shoenoides). However, theresponse of other wetland plant species to pre-scribed burning depended upon the coincidenteffects of moisture and salinity-alkalinity gra-dients. Given this interactive dependency, theuse of fire to promote certain plant species has,not surprisingly, produced mixed results (Pen-dergrass et al. 1999). We suggest that effectivemanagement of complex ecological systems likewetlands requires the use of experimentalstudies such as ours to determine the directand indirect effects of certain managementactivities.

Like the management of many other eco-systems, wetland management typically involvesimplementation of multiple activities. The ob-jectives of wetland management at our studysite are typical of many managed wetlands andinclude (1) enhancement of native plant species,(2) control of invasive introduced plant spe-cies (e.g., P. arundinacea), and (3) provision ofappropriate habitat for native fauna. Prescribedburning in fall combined with flooding inspring achieves the latter goal because burn-ing removes residual cover and makes newspring growth of plants available to geese, andflooding provides safe roost sites adjacent tofeeding areas. Prescribed burning combinedwith flooding does not increase the proportionof native versus introduced plant species, al-though some native species (e.g., H. jubatum)

314 WESTERN NORTH AMERICAN NATURALIST [Volume 67

were enhanced by burning. Control of P. arundi-nacea in these wetland plant communities maybe possible if prescribed fall burning is fol-lowed by flooding in spring, although furtherstudy of the interaction between burning andflooding on the abundance of this invasiveintroduced species is needed.

ACKNOWLEDGMENTS

We thank Dave Boyd and Steve Moore forlogistical help with the burning. Jeff Davis,Roger Jones, Ed Burns, and Karen Boldahelped with data collection. Special thanks goto Jack Sloat and Pacific Gas and ElectricCompany for equipment, power, and hospital-ity, and to J. Taylor, K. Novik, D. Connelly, andD. Yparraguirre of the California Departmentof Fish and Game for outstanding field sup-port. Funding was provided by the CaliforniaDepartment of Parks and Recreation, the Cali-fornia Department of Fish and Game, PacificGas and Electric Company, and the Universityof California at Davis.

LITERATURE CITED

ALTMANN, J. 1974. Observational study of behavior: sam-pling methods. Behaviour 49:227–267.

BADGER, K.S., AND I.A. UNGAR. 1989. The effects of salin-ity and temperature on the germination of the inlandhalophyte Hordeum jubatum. Canadian Journal ofBotany 67:1420–1425.

______. 1991. Life history and population dynamics ofHordeum jubatum along a soil salinity gradient. Cana-dian Journal of Botany 69:384–393.

BAKKER, J.P. 1985. The impact of grazing on plant commu-nities, plant populations, and soil conditions on salt-marshes. Vegetatio 63:391–398.

BAZELY, D.R., AND R.L. JEFFERIES. 1986. Changes in thecomposition and standing crop of salt-marsh com-munities in response to removal of a grazer. Journalof Ecology 74:693–706.

BERTNESS, M.D. 1991. Interspecific interactions amonghigh marsh perennials in a New England salt marsh.Ecology 72:125–137.

BERTNESS, M.D., AND A.M. ELLISON. 1987. Determinantsof pattern in a New England salt marsh plant com-munity. Ecological Monographs 57:129–147.

BMDP. 1992. Bio-medical programs, release 7.0. Statisti-cal Solutions, Inc., Saugus, MA.

BOND, W.J., AND R.W. VAN WILGREN. 1996. Fire andplants. Chapman and Hall, New York.

BROTHERSON, J.D. 1987. Plant community zonation in re-sponse to soil gradients in a saline meadow near UtahLake, Utah County, Utah. Great Basin Naturalist 47:322–333.

CANOCOTM. 1989. CANOCO software. MicrocomputerPower, Cornell University, Ithaca, NY.

COWIE, N.R., W.J. SUTHERLAND, M.K.M. DITLHOGO, AND

R. JAMES. 1992. The effects of conservation manage-

ment of reed beds. II. The flora and litter disappear-ance. Journal of Applied Ecology 29:277–284.

DE SZALAY, F.A., AND V.H. RESH. 1997. Responses of wetlandinvertebrates and plants important in waterfowl dietsto burning and mowing of emergent vegetation.Wetlands 17:149–156.

FERRARI, C.A. 1994. Soil survey of Intermountain Area,California. USDA National Resources ConservationService, Washington, DC.

FIENBERG, S.E. 1970. The analysis of multidimensionalcontingency tables. Ecology 51:419–433.

FOOTE, A.L., J.A. KADLEC, AND B.K. CAMPBELL. 1988.Insect herbivory on an inland brackish wetland. Wet-lands 8:67–74.

FREDRICKSON, L.H., AND M.K. LAUBHAN. 1996. Managingwetlands for wildlife. Pages 623–647 in T.A. Bookhout,editor, Research and management techniques forwildlife and habitats. The Wildlife Society, Bethesda,MD.

FREDRICKSON, L.H., AND T.S. TAYLOR. 1982. Managementof seasonally flooded impoundments for wildlife.U.S. Fish and Wildlife Service, Resource Publication148.

FULLER, D.A., C.E. SASSER, W.B. JOHNSON, AND J.G. GOS-SELINK. 1985. The effects of herbivory on vegetationon islands in Atchafalaya Bay, Louisiana. Wetlands 4:105–114.

GIBBS, J.P., H.L. SNELL, AND C.E. CAUSTON. 1999. Effec-tive monitoring for adaptive wildlife management:lessons from the Galapagos Islands. Journal of Wild-life Management 63:1055–1065.

GIVENS, L.S. 1962. Use of fire on southeastern wildliferefuges. Proceedings of the Tall Timbers Fire EcologyConference 1:121–126.

GLENN-LEWIN, D.C., R.K. PEET, AND T.T. VEBLEN. 1992.Plant succession: theory and prediction. Chapmanand Hall, New York.

GOODWIN, T.M. 1979. Waterfowl management practicesemployed in Florida and their effectiveness on nativeand migratory waterfowl populations. Florida Scien-tist 42:123–129.

HADLEY, E.B. 1970. Net productivity and burning responseof native eastern North Dakota prairie communities.American Midland Naturalist 84:121–135.

HANSEN, D.J., P. DAYANANDAN, P.B. KAUFMAN, AND J.D.BROTHERSON. 1976. Ecological adaptations of saltmarsh grass, Distichlis spicata (Gramineae), and en-vironmental factors affecting its growth and distribu-tion. American Journal of Botany 63:635–650.

HANSON, H.C. 1939. Fire in land use management. Ameri-can Midland Naturalist 21:415–434.

HICKMAN, J.C., EDITOR. 1993. The Jepson manual. Higherplants of California. University of California Press,Berkeley.

HOBBS, N.T., D.S. SCHIMEL, C.E. OWENSBY, AND D.S.OJIMA. 1991. Fire and grazing in the tallgrass prairie:contingent effects on nitrogen budgets. Ecology 72:1374–1382.

HOLLING, C.S., EDITOR. 1978. Adaptive environmentalassessment and management. John Wiley & Sons,New York.

JENKINS, S.H. 1975. Food selection by beavers: a multidi-mensional contingency table analysis. Oecologia 21:157–173.

JOHNSON, S.R., AND A.K. KNAPP. 1995. The influence offire on Spartina pectinata wetland communities in a

2007] EFFECTS OF BURNING ON WETLAND PLANTS AND GRAZING GEESE 315

northeastern Kansas tallgrass prairie. Canadian Jour-nal of Botany 73:84–90.

KADLEC, J.A., AND L.M. SMITH. 1989. The Great Basinmarshes. Pages 451–474 in L.M. Smith, R.L. Peder-son, R.M. Kaminski, editors, Habitat managementfor migrating and wintering waterfowl in North Amer-ica. Texas Tech University Press, Lubbock.

KANTRUD, H.A. 1986. Effects of vegetation manipulationon breeding waterfowl in prairie wetlands—a litera-ture review. U.S. Department of the Interior, Fishand Wildlife Technical Report No. 3.

KIRBY, R.E., S.J. LEWIS, AND T.N. SEXSON. 1988. Fire inNorth American wetland ecosystems and fire-wild-life relations: an annotated bibliography. U.S. Fishand Wildlife Service, Biological Report 88.

KIRKMAN, L.K., AND R.R. SHARITZ. 1994. Vegetation dis-turbance and maintenance of diversity in intermit-tently flooded Carolina Bays in South Carolina. Eco-logical Applications 4:177–188.

KOZLOWSKI, T.T., AND C.E. AHLGREN, EDITORS. 1974. Fireand ecosystems. Academic Press, New York.

KUSHLAND, J.A. 1990. Freshwater marshes. Pages 324–363in R.L. Myers and J.J. Ewel, editors, Ecosystems ofFlorida, University of Central Florida Press, Orlando.

LAUBHAN, M.K. 1995. Effects of prescribed fire on moist-soil vegetation and soil macronutrients. Wetlands 15:159–166.

LUKEN, J.O. 1990. Directing ecological succession. Chap-man and Hall, New York.

LYNCH, J.J. 1941. The place of burning in management ofthe Gulf Coast wildlife refuges. Journal of WildlifeManagement 5:454–457.

LYON, L.J., AND P.F. STICKNEY. 1976. Early vegetal succes-sion following large northern Rocky Mountain wild-fires. Proceedings of the Tall Timbers Fire EcologyConference 14:355–373.

MARTZ, G.F. 1967. Effects of nesting cover removal onbreeding ducks. Journal of Wildlife Management31:236–247.

MCATEE, J.W., C.J. SCIFRES, AND D.L. DRAWE. 1979a.Improvement of Gulf cordgrass range with burningor shredding. Journal of Range Management 32:372–375.

______. 1979b. Digestible energy and protein content ofGulf cordgrass following burning or shredding. Jour-nal of Range Management 32:376–378.

MENGES, E.S., AND C.V. HAWKES. 1998. Interactive effectsof fire and microhabitat on plants of Florida scrub.Ecological Applications 8:935–946.

MILLER, D.L., F.E. SMEINS, J.W. WEBB, AND M.T. LONG-NECKER. 1997. Regeneration of Scirpus americanusin a Texas coastal marsh following Lesser Snow Gooseherbivory. Wetlands 17:31–42.

MUELLER-DOMBOIS, D., AND H. ELLENBERG. 1974. Aimsand methods of vegetation ecology. John Wiley &Sons, Inc., New York.

NOBLE, I.R., AND R.O. SLATYER. 1980. The use of vitalattributes to predict successional changes in plantcommunities subject to recurrent disturbances. Veg-etatio 43:5–21.

PACKARD, S., AND C.F. MUTEL. 1997. Perspective. Pages9–18 in S. Packard and C.F. Mutel, editors, The tall-grass restoration handbook. Island Press, Washing-ton, DC.

PALMER, M.W. 1993. Putting things in even better order:the advantages of canonical correspondence analysis.Ecology 74:2215–2230.

PAYNE, N.F. 1992. Techniques for wildlife habitat manage-ment of wetlands. McGraw-Hill, Inc., New York.

PEDERSON, R.L., D.G. JORDE, AND S.G. SIMPSON. 1989.Northern Great Plains. Pages 181–202 in L.M. Smith,R.L. Pederson, and R.M. Kaminski, editors, Habitatmanagement for migrating and wintering waterfowlin North America, Texas Tech University Press, Lub-bock.

PENDERGRASS, K.L., P.M. MILLER, J.B. KAUFFMAN, AND

T.N. KAYE. 1999. The role of prescribed burning inmaintenance of an endangered plant species, Loma-tium bradshawii. Ecological Applications 9:1420–1429.

PHILLIPS, J.R.V. 1934. Succession, development, the cli-max and the complex organism: an analysis of con-cepts. Part I. Journal of Ecology 22:88–105.

______. 1935a. Succession, development, the climax andthe complex organism: an analysis of concepts. PartII. Journal of Ecology 23:210–223.

______. 1935b. Succession, development, the climax andthe complex organism: an analysis of concepts. PartIII. Journal of Ecology 23:554–571.

PICKETT, S.T.A., S.L. COLLINS, AND J.J. ARMESTO. 1987.Models, mechanisms and pathways of succession.Botanical Review 53:335–371.

PICKETT, S.T.A., AND R.S. OSTFELD. 1995. The shiftingparadigm in ecology. Pages 261–278 in R.L. Knightand S.F. Bates, editors, A new century for naturalresources management. Island Press, Washington,DC.

RAVEN, P.H. 1988. The California flora. Pages 109–137 inM.G. Barbour and J. Major, editors, Terrestrial vege-tation of California. California Native Plant Society,Special Publication Number 9, Sacramento.

SALE, P.J.M., AND R.G. WETZEL. 1983. Growth and metab-olism of Typha species in relation to cutting treat-ments. Aquatic Botany 15:321–334.

SCHMALZER, P.A., AND C.R. HINKLE. 1993. Effects of fireon nutrient concentrations and standing crops inbiomass of Juncus roemerianus and Spartina bakerimarshes. Castanea 58:90–114.

SCHMALZER, P.A., C.R. HINKLE, AND J.L. MAILANDER. 1991.Changes in community composition and biomass inJuncus roemerianus Scheele and Spartina bakeri Merr.marshes one year after a fire. Wetlands 11:67–86.

SIMPSON, E.H. 1949. Measurement of diversity. Nature163:688.

SKOUGARD, M.G., AND J.D. BROTHERSON. 1979. Vegeta-tional response to three environmental gradients inthe salt playa near Goshen, Utah County, Utah. GreatBasin Naturalist 39:44–58.

SMITH, L.M., AND J.A. KADLEC. 1985a. Fire and herbivoryin a Great Salt Lake marsh. Ecology 66:259–265.

______. 1985b. Comparisons of prescribed burning andcutting of Utah marsh plants. Great Basin Naturalist45:462–466.

SMITH, L.M., J.A. KADLEC, AND P.V. FONNESBECK. 1984.Effects of prescribed burning on nutritive quality ofmarsh plants in Utah. Journal of Wildlife Manage-ment 48:285–288.

SMITH, L.M., R.L. PEDERSON, AND R.M. KAMINSKI, EDI-TORS. 1989. Habitat management for migrating andwintering waterfowl in North America. Texas TechUniversity Press, Lubbock.

TAYLOR, K.L., J.B. GRACE, G.R. GUNTENSPERGEN, AND A.L.FOOTE. 1994. The interactive effects of herbivoryand fire on an oligohaline marsh, Little Lake, Louisi-ana, USA. Wetlands 14:82–87.

316 WESTERN NORTH AMERICAN NATURALIST [Volume 67

TER BRAAK, C.J.F., AND I.C. PRENTICE. 1988. A theory ofgradient analysis. Advances in Ecological Research18:271–317.

TOFT, C.A. 1984a. Activity budgets in two species of beeflies (Lordotus: Bombyliidae, Diptera): a comparisonof species and sexes. Behavioral Ecology and Socio-biology 14:287–296.

______. 1984b. Resource shifts in bee flies (Bombyliidae):interactions among species determine choice of re-sources. Oikos 43:104–112.

UHLER, F.M. 1944. Control of undesirable plants in water-fowl habitats. Transactions of the North AmericanWildlife Conference 9:295–303.

VAN DER VALK, A.G. 1986. The impact of litter and annualplants on recruitment from the seed bank of a lacus-trine wetland. Aquatic Botany 24:13–26.

WALTERS, C.J. 1986. Adaptive management of renewableresources. Macmillan Publishing Company, New York.374 pp.

WALTERS, C.J., AND C.S. HOLLING. 1990. Large-scale man-agement experiments and learning by doing. Ecology71:2060–2068.

WELLER, M.W. 1994. Freshwater marshes: ecology andwildlife management. 3rd edition. University of Min-nesota Press, Minneapolis.

WHELAN, R.J. 1995. The ecology of fire. Cambridge Uni-versity Press, New York.

WILLARD, E.E., AND R.H. WAKIMOTO. 1995. Vegetationrecovery in sedge meadow communities within theRed Bench Fire, Glacier National Park. Pages 102–110 in S.I. Cerulean and R.T. Engstrom, editors, Firein wetlands: a management perspective. Proceed-ings of the Tall Timbers Fire Ecology Conference,No. 19., Tall Timbers Research Station, Tallahassee,FL.

WRIGHT, H.A., AND A.W. BAILEY. 1982. Fire ecology: UnitedStates and southern Canada. John Wiley & Sons,Inc., New York.

ZAR, J.H. 1999. Biostatistical analysis. 4th edition. Pren-tice Hall, Upper Saddle River, NJ.

Received 11 May 2005Accepted 17 July 2006

2007] EFFECTS OF BURNING ON WETLAND PLANTS AND GRAZING GEESE 317