Effects of fire at two levels of intensity on beetle diversity in shortgrass steppe were examined. The experimental design was completely randomized, with 3 treatments and 4 replicates per treatment. Treatments were two levels of fire 1) dormant-season fire (relatively hot), and 2) growing-season fire (relatively cool), and unburned plots. The response variables were arthropod species richness and abundance. The intermediate disturbance hypothesis predicts that maximum species richness occurs at intermediate levels of disturbance. Data obtained in this study support that prediction. Species richness was higher on plots of intermediate fire intensity than the more intensely burned plots, and almost twice as high as unburned plots. Abundance did not significantly differ among treatments

Ford, Paulette L.

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University of Kentucky

University of Kentucky UKnowledge International Grassland Congress Proceedings XIX International Grassland Congress Biodiversity and Fire in Shortgrass Steppe Paulette L. Ford Rocky Mountain Research Station Follow this and additional works at: https://uknowledge.uky.edu/igc  Part of the Plant Sciences Commons, and the Soil Science Commons This document is available at https://uknowledge.uky.edu/igc/19/23/2 This collection is currently under construction. The XIX International Grassland Congress took place in São Pedro, São Paulo, Brazil from February 11 through February 21, 2001. Proceedings published by Fundacao de Estudos Agrarios Luiz de Queiroz This Event is brought to you for free and open access by the Plant and Soil Sciences at UKnowledge. It has been accepted for inclusion in International Grassland Congress Proceedings by an authorized administrator of UKnowledge. For more information, please contact UKnowledge@lsv.uky.edu. ID # 23-02BIODIVERSITY AND FIRE IN SHORTGRASS STEPPEP. L. FordRocky Mountain Research Station, 2205 Columbia SE, Albuquerque, New Mexico 87106, USA,and University of Arizona, School of Renewable Natural Resources, Tucson, Arizona 85721,USA, plford@fs.fed.usAbstractEffects of  fire at two levels of intensity on beetle diversity in shortgrass steppe wereexamined. The experimental design was completely randomized, with 3 treatments and 4 replicatesper treatment.  Treatments were two levels of fire 1) dormant-season fire (relatively hot), and 2)growing-season fire (relatively cool), and unburned plots.  The response variables were arthropodspecies richness and abundance.  The intermediate disturbance hypothesis predicts that maximumspecies richness occurs at intermediate levels of disturbance. Data obtained in this study  support  thatprediction.  Species richness was higher on plots of intermediate fire intensity than the more intenselyburned plots, and almost twice as high as unburned plots.  Abundance did not significantly differamong treatments.Keywords: Fire, disturbance, shortgrass steppe, biodiversity, arthropod, Coleoptera, beetlesIntroductionIn ecological terms fire is a disturbance.  A disturbance is an event that may, directly orindirectly, disrupt a community and change resource availability (White and Picket, 1985). Disturbance can increase species  richness by increasing spatial heterogeneity within an area, and bycreating gaps in communities that allow recolonization of the gaps by individuals of the same ordifferent species.  Even though infrequent to moderately frequent disturbances enhance diversity,extremely frequent disturbances can be so destructive that they operate in the reverse to reducediversity;   therefore,  diversity is predicted to  peak at intermediate levels of disturbance (Connell,1978;  Pianka, 1994). The order Coleoptera (beetles) contains a third of all known insects- 300,000 speciesworldwide and ~30,000 species in North America  (Milne and Milne, 1996).  Beetles are conspicuouscomponents of the terrestrial invertebrate fauna of arid and semi-arid ecosystems of North America(Allsopp, 1980). They have an important role in the functioning of the  shortgrass steppe ecosystem,serving as predators, prey, scavengers and parasites.  In addition, many plant-feeding  species attack plants and stored foods, while others pollinate flowers and eat plant pests.  My experimental researchexamined the effect of  fire at two levels of intensity on beetle diversity in shortgrass steppe.Material and MethodsThe study site was in shortgrass steppe of the southern Great Plains on the Kiowa NationalGrassland (36° 30'N, 103° 7'W) in northeastern New Mexico.  Almost all of the grassland on theplains in the Southwest is composed of mixed or shortgrass communities (Brown, 1994).  While thesecommunities have been considerably altered by grazing and the results of this practice (firesuppression followed by shrub invasion), much of the grassland remains an uncluttered perennial grassdominated landscape (Brown, 1994). It is estimated that less than 23% of true shortgrass steppe in the United States still exists innative vegetation (National Grasslands Management Review Team, 1995).  My study site, locatedin the far northeastern corner of New Mexico, is one such area.  My site consists of approximately160 ha of shortgrass steppe that has never been plowed, though it was grazed by livestock until 1990. The site is relatively homogeneous and nearly flat.  Elevation ranges from 1,455 m at the southwestcorner to 1,472 m at the northwest corner of the site.  Mean annual precipitation is 391 mm.  Themajority of precipitation occurs from May through September, with peak rainfall in July. Overall, thedeep, well-drained loam soils on the site support and almost shrubless grassland with a relatively tightsod of buffalograss (Buchloe dactyloides (Nutt.) Engelm.) and blue grama (Bouteloua gracilis(H.B.K.) Lag.)  These species average 85% of the cover through out the site.The research experimental design was completely randomized, with 3 treatments and 4replicates per treatment.  Treatments were two levels of fire 1) dormant-season fire, and 2) growing-season fire, and unburned plots.  The response variables were arthropod species richness andabundance. Treatments were randomly assigned to 12 2-ha plots.  Treatments were applied in 1997. Dormant-season fire (level 1) occurred in April, when moisture was low and fine fuel was cured. Growing-season fire (level 2) occurred in July  when vegetation was green and moisture was high. Pre-treatment sampling took place in March, post-burn sampling began two weeks after firetreatment. Surface-active beetles were captured with pitfall traps, 1-pint paint cans set into the groundwith the opening flush with the ground surface.  Pitfalls were placed 30 m apart .  Propylene glycolwas used as the preservative.  Twenty pitfalls per plot, for a total of 240 pitfalls, were open twoweeks, once a month for 6 months in 1997 (March - October) and from July-October 1998.  Pitfallsare biased toward the capture of solitary wandering species and against those with low mobility (Uetzand Unzicker, 1976;  Baars, 1979;  Halsall and Wratten, 1988) or that live in colonies (Marsh, 1984). Therefore, this collecting method by itself does not account for all of the site’s diversity, even ofsurface-dwelling species.  Beetles were identified to species, and number of individuals for eachspecies was tallied. Permutation methods in SAS PROC MULTTEST (SAS Institute Inc., 1989-1996)  were usedfor sets of three pairwise comparisons among treatments and across sample periods forpre-treatment data (March 1997) and post-treatment data from July-October 1998.    Results and DiscussionBeetle samples were composed of 29 families, 115 species, and 4,608 individuals.  Tenspecies from six families, made up 90% of the individuals (Table 1).  Pre-treatment measures ofspecies richness and abundance revealed no significant differences among the 12 experimental plots(Table 2). Approximately one year and six months after dormant-season fire (level 1), and one year andthree months after growing-season fire (level 2) species richness significantly differed amongtreatments; growing-season fire treated plots had a significantly higher number of beetle species thanunburned plots.  Species richness was also higher on growing-season plots versus dormant-seasonplots, but the difference was not significant.  Abundance did not significantly differ among treatments(Table 2).       The intermediate disturbance hypothesis predicts that maximum species richness occurs atintermediate levels of disturbance because 1) high disturbance levels allow persistence of thosespecies that are disturbance-adapted or in this case fire adapted, and  2) low disturbance levels allowcompetitive dominance by some species, causing local extinctions of others.  However, many speciescan coexist and persist at intermediate levels of disturbance.  My data support that prediction.  Firesduring the dormant-season (level 1), when fuel was cured and moisture was low, appeared to burnhotter and faster, and more completely than growing-season fires.  Growing-season fires appearedto burn unevenly in a patchy manner, slow, smoky, and cool because of the green vegetation and highsoil moisture content.  Level 1 represented a higher level of disturbance than level 2, whichrepresented an intermediate level of disturbance.  Unburned plots represented a low level ofdisturbance.  Species richness was higher on plots of intermediate fire intensity than the moreintensely burned plots, and almost twice as high as unburned plots.ReferencesAllsopp, P. G. (1980).  The biology of false fireworms and their adults (soil-inhabitingTenebrionidae) (Coleoptera): a review.  Bull. Entomol. Res. 70:343-379.Baars, M. A.  (1979).  Catches in pitfall traps in relation to mean densities of carabid beetles. Oecologia 41:251-259.Brown, D. E.  (1994).  Biotic communities: southwestern United States and northwestern Mexico. University of Utah Press, Salt Lake City, p. 342.Connell, J. H.  (1978).  Diversity in tropical rainforests and coral reefs.  Science 199:1302-1310.Halsall, N. B. and Wratten S. D.  (1988).  The efficiency of pitfall trapping for polyphagouspredatory Carabidae.  Ecological Entomology 13:293-299.Marsh, A. C.  (1984).  The efficacy of pitfall traps for determining the structure of a desert antcommunity.  Journal of the Entomological Society of South Africa 47:115-120.Milne, L. and Milne M. (1996).  National Audubon Society Field Guide to North                         American Insects and Spiders.  Alfred A. Knopf, New York, p. 989.National Grasslands Management Review Team.  (1995).  National Grasslands ManagementReview Report.  October 30 - November 8.  USDA Forest Service Report, Washington, D. C.Pianka, E. R.  (1994).  Evolutionary Ecology.  HaperCollins College Publishers, p. 486.SAS Institute Inc.  (1989-1996).  The SAS System for Windows Release 6.12.  Cary, NC, USA.Uetz, G. W. and Unzicker J. D.  (1976).  Pitfall trapping in ecological studies of wandering spiders. Journal of Arachnology 3:101-111.White, P. S. and Pickett S. T. A.  (1985).  Natural disturbance and patch dynamics: an introduction.  Pages 3-13 in S. T. A. Pickett and P. S. White, eds. The Ecology of Natural Disturbance and PatchDynamics.  Academic Press,  Orlando, FL.Table 1 -   Beetle relative abundance (%): total number of individuals per species compared                 to the total number of individuals of all other beetles species combined.Family Species Relative Abundance (%)Carabidae Cicindela obsoleta                  3Pasimachus californicus                  4Pasimachus obsoletus                  1Curculionidae undetermined                  1Elateridae Agrypnus rectangularis                  9Nitidulidae Carpophilus lugubris                  66Scarabaeidae Euphoria kerni                  1Neopsammodius interruptus                  3Phyllophaga glabricula                  2Tenebrionidae Eusattus convexus                  2Other                  8Total                  100Table 2 -   Results of MULTTEST analysis of beetle (Coleoptera) abundance and richness in whichfire season (dormant-season, growing-season) or unburned were treated as the independent variables,and number of beetle individuals and species as the dependent variables.  " = 0.05.______________________________________________________________________________Abundance______________________________________________________________________________Period1              Treatment    Abundance            CONTRAST2               P Value                              (N)                            Mean (SD)______________________________________________________________________________Period 1 Unburned (4)          42(28)      U vs D  0.83Dormant-season (4)          73(56)      U vs G  0.98Growing-season (3)          60(26)      D vs G  0.99 Period 2 Unburned (4)         297(80)         U vs D  1.00Dormant-season (4)         317(76)      U vs G  0.91Growing –season(3)           376(189)                   D vs G                      0.97RichnessTreatment (N) AbundanceMean (SD)CONTRAST P VAluePeriod 1 Unburned (4) 7(1) U vs D 0.99Dormant-season (4) 8(1) U vs G 0.55Growing-season (3) 10 (4) D vs G 0.68Period 2 Unburned (4) 16(3) U vs D 0.75Dormant-season (4) 20 (3) U vs G 0.04Growing-season (4) 25 (5) D vs G 0.341Period 1 = pre-treatment, March 1997. Period 2 = July-October 1998.2U = unburned, D = dormant-season fire treatment, G = growing – season treatment.

Biodiversity and Fire in Shortgrass Steppe

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Biodiversity and Fire in Shortgrass Steppe

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