Butterfly Inventory and Assessment of the Effects of Fire and Grazing Managements on the Tallgrass Prairie National Preserve; an Initial Analysis.

Transcription

1 Butterfly Inventory and Assessment of the Effects of Fire and Grazing Managements on the Tallgrass Prairie National Preserve; an Initial Analysis. Greg Sievert and Jeff Prendergast Emporia State University Department of Biology 1200 Commercial Street Emporia, Kansas Submitted: 14 March 2011

2 Introduction Tallgrass prairie once covered over 500,000 km 2 in North America (Kuchler 1964) but has since been reduced by over 90% (Howe 1994, Kaiser 1998). Further reduction of the tallgrass prairie continues through practices of overgrazing, conversion to cultivated agriculture, development, and woody plant invasion and remaining patches of this habitat have become increasing isolated (Howe 1994). This habitat destruction and isolation is threatening the persistence of many prairie obligate species. Herkert (1995) documented >50% declines in the populations of many grassland birds from Research on prairie butterflies has been less extensive than for prairie birds, but prairie obligate butterflies have experienced similar declines along the edges of their range and within their core habitat (Swengle 1990, Kocher and Williams 2006). Species such as the Ottoe Skipper (Hesperia ottoe), and Regal Fritillary (Speyeria idalia) are prairie obligates whose populations are in severe decline (Hammond and McCorkle 1983, Swengel 1993). These declines in butterfly populations have invoked six tallgrass prairie butterfly species to be listed in the Kansas Comprehensive Wildlife Conservation Plan list as "species of greatest conservation need" (Wasson et al. 2005). In addition to the direct loss of habitat, additional threats to prairie butterflies include unsuitable fire management and herbicide use and invasive plant species out-competing native nursery and forage species (Panzer et al. 1995, Swengel 2001, Samways et al. 2005). The survival of prairie obligate species is reliant on remnant fragments of prairie in protected areas such as the Tallgrass Prairie National Preserve (TAPR). The TAPR encompasses around 10,894 acres of land within the Flint Hills of Kansas. The Flint Hills region is the largest remaining continuous expanse of native tallgrass prairie in North America. Nearly two-thirds of the remaining tallgrass prairie is found here. Although the Flint Hills constitutes one of the larger tracts of tallgrass prairie remaining, overutilization of prairie resources has threatened the habitat integrity of the remaining rangeland (Knopf 1994, Samson and Knopf 1994) and intensive management and close-monitoring of the prairie community will likely be necessary to maintain the prairie resources. From the 1980's until 2006, the area that is now the TAPR performed early spring annual burns and cattle were double stocked for the first half of the growing season, much like most other ranches in the Flint Hills. This grazing system is known as Intensive Early Stocking (IES). While IES coupled with spring burns is economically advantageous to ranchers, the homogeneous landscape it creates may not be the most ideal range practice for maximizing grassland plant and animal diversity. Researchers have suggested that IES paired with annual spring burns - 2 -

3 may be responsible for declines in vertebrate species (Kaufman and Kaufman 1997, Robbins et al. 2002). To promote grassland heterogeneity at the TAPR preserve managers initiated a patch-burn grazing (PBG) system on approximately 3,800 acres in The pasture that was to get the patch-burn was divided into three sub-units so that approximately one-third of the pasture is burned on a 3-year rotational basis. This creates variation in the vegetation structure within the pasture. Because cattle preferentially graze on recently burned areas, the unburned sections of the pasture are essentially rested allowing for litter build-up. The interaction between fire and grazing creates an ever-changing combination of burned and unburned, grazed and ungrazed areas, often referred to as a "shifting mosaic". The PBG system results in increased heterogeneity across the landscape, providing habitat for a broader range of grassland species (Fuhlendorf 2006). Invertebrates have often been used as indicators of habitat quality (Pyle et al. 1981, Samways 1994). Butterflies are useful for evaluating the ecosystem health of natural areas because of their sensitivity to environmental variation, rapid population response to habitat change, relative ease of field identification, and tight link with host and nectar plants (Scoble 1992, Dietrich et al. 1998, Simonson et al. 2001, Pywell et al. 2004, Poyry et al., 2005). Butterfly diversity and other inventory metrics have been utilized as indicators to assess the effects of habitat management (Swengel 1996), variation in plant diversity (Spitzer et al. 1997), impacts of habitat disturbance (Dennis and Hardy 2001, Kocher and Williams 2006), and for rapid evaluation of biodiversity in threatened habitats (Kerr et al. 2000). Grassland birds were selected as one indicator of overall prairie ecosystem quality by The National Park Service Heartland Inventory and Monitoring program. While bird populations can provide information on ecosystem condition, the migratory nature of many bird species means that their presence/abundance can be affected by conditions beyond the area of interest. However, most butterfly species go through their entire life cycle within a few miles (Moffat and McPhillips 1993). Surveying for the presence and changes in butterfly abundance over time could provide additional information regarding success of management and conservation trends at the TAPR. Just as the TAPR may provide a sufficient tract and heterogeneity of prairie for vertebrates (Powell 2000), it may also prove to be an invaluable refugia for prairie butterflies

4 The objective of this project was two-fold. First, we wanted to establish the current butterfly community composition within the TAPR. Secondly, we evaluated butterfly species diversity between the PBG and IES grazing systems on the TAPR. We hypothesized that the species diversity of butterflies would be higher on all three patches on the PBG than in the IES grazing system in accordance with the increases in habitat heterogeneity. Likewise, we also anticipated seeing more prairie specialists within the PBG than in the IES grazing system

5 Methods Butterfly monitoring protocols developed for four prairie parks (Debinski et al. 2000) were used to document the current butterfly community at TAPR and to evaluate the impact on butterfly diversity of management practices being instituted on the preserve. The protocol calls for standard transect techniques (Pollard and Yates 1993) that have been used extensively (Beavers and Ramsey 1998) and are thought to provide good estimates of butterfly species richness and abundance (Swengel 1996, Natuhara et al. 1998, Mahady 1999). Patch-burn management was initiated on the preserve in 2006 in a 3,831 acre pasture referred to as Big Pasture. Consequently, the present study began in the second, 3-year cycle of patch-burn grazing management. Two Section Pasture has had IES and annual burning for many years but it also had season long grazing in 2006, 2007, and Transects were established in four different management units (Fig. 1) on the TAPR. In Big Pasture, there were three different patch-burn grazing units: Burned 2010; Burned One Year Post-burn; and Burned Two Year Post-burn that had butterfly transects (Fig.2). Two Section Pasture (IES Annually Burned) was used as the representative of traditional management for butterfly transects (Fig.3). Based on recommendations by Debinski et al. (2000) we used six transects per management unit. The 24 transects were 5 by 50 m and were located at least 50 m apart. In each management unit, some transects were oriented against the prevailing wind (E -W) and some were oriented with the prevailing wind (N-S). Transects were established in April 2010 after the management units were burned and the cattle were stocked. Surveys were conducted during a seven to ten day period each month, from May through September. Each month the 24 transects were each surveyed six times with at least a 15 minute rest period between surveys for a total transect walking time of 30 minutes for each transect. We walked each 50 m transect at a constant pace of 10 m per minute and counted butterflies that were within a 5 m box around the observer (2.5 m on each side of the observer). Transect walks were undertaken between 10:00 am and 5:00 pm CDT and only when the temperature was above 18 C (66 F). Surveys were curtailed whenever cloud cover was estimated to be above 70% or when the average wind speed exceeded 32 kph (20 mph) or wind gusts exceeded 40 kph (25 mph). In addition, at least once a month we spent time at Palmer Creek and Fox Creek which were outside of our fire managed prairie study areas (Fig 1). We censused these forested riparian habitats for butterflies in the hopes of increasing the total number of known butterfly species found at the TAPR. No additional new - 5 -

6 species were found at Fox Creek that were not also found at Palmer Creek so it is not included in our results. Statistical Analyses Since some transects were oriented N-S and some E-W, we used a simple T- test to test for differences in butterfly diversity and butterfly abundance between the transect orientations. We did this analysis with the statistical package SAS (SAS Institute, Cary, NC) using Proc TTEST. A Simpson Diversity Index, corrected for a finite population (Krebs 1999), was used to calculate the diversity of butterflies for each transect, each month. If no butterflies were observed on a transect during a survey it was treated as missing data. We used an analysis of variance (ANOVA) with months as blocks to test for differences among the four treatments in butterfly diversity. We did this analysis with the statistical package SAS using Proc GLM. All P-values were considered significant at the a priori level of α =

7 Results We observed a total of 1712 butterflies of 34 species along the 24 transects. An additional 17 species were observed on the preserve that were never observed during transect surveys and thus not enumerated (Table 1). There was no significant difference in either butterfly abundance (P=0.881) or diversity (P=0.574) between the transects that were set with the prevailing wind (N-S) and those that were set against the prevailing wind (E-W). While the overall butterfly diversity was highest in the area that was burned in 2009 (1 year post-burn), the diversity was higher in other plots during certain months (Table 2). There was a significant blocking effect of month (F 4,112 = 6.24; P<0.001). Butterfly diversity appeared to follow a bimodal distribution with the highest diversities in June and September (Fig.4). There was a significant difference in the butterfly diversity among the four treatments (F 3,112 = 12.02; P<0.001), with butterfly diversity being lowest on annually burned intensively grazed site and highest on the area burned in 2009 (1 year post-burn) (Fig.5)

8 Discussion Butterfly diversity was higher in all three treatments of the patch-burn grazing pasture than in the traditionally managed pasture, however not significantly different between the traditionally managed field and the patch that was unburned for two years. These results are as expected, but still slightly surprising. Contrary to our expectations the butterfly diversity on the traditional management annual burned site was most similar to the patch that had been unburned for two years as opposed to the patch that was burned in the same year. Combinations of fire and grazing can increase the diversity of herbaceous plants (Hickman et al. 2004). So it is likely that the two years of rest prior to being burned increased the diversity of herbaceous plants, and thus food resources for butterflies, which could account for the differences in diversity we observed between the two pastures burnt in the same year. According to our results the patch-burn grazing system has increased the overall diversity of butterflies. With no significant difference between the annual burned patch and the patch that had been unburned for two years it might seem feasible to consider a 2-year burn cycle (Fig. 5). However, nearly half of the Regal Fritillaries, an important prairie obligate, were found in the patch that had been unburned for two years. Additionally, increasing the burn frequency would likely impact the diversity of herbaceous plants on all burn units (Hartnett et al. 2004; Hickman et al. 2004). In addition to the confirmed species that we found on the preserve (Table 1), there were also four species that we observed but were unable to catch to confirm. Our unconfirmed sightings included the Gulf Fritillary (Agraulis vanilla), Marine Blue (Leptotes marina), Northern Cloudywing (Thorybes pylades), and the Common Sootywing (Pholisora catullus). In addition to our unconfirmed sightings, Table 3 gives several other species that were not observed but could potentially occur in this area (Dole et al. 2004). Some of these species may have been present within the TAPR but remained undetected due to time and location of surveys or they could have occurred at low enough densities to avoid detection with our sampling protocol. Alternatively, some of these species (i.e. soapberry hairstreak) may have been absent from the TAPR due to inadequate resources

9 When interpreting our results, it is important to recognize that our conclusions are based on a single season of observations and do not take into account any inter-annual variation that may occur. Additionally, given the design of management practices on the TAPR there is only one replicate of each treatment that was allotted for assessment of butterfly diversity, thus true replication was unattainable. Therefore, unusual conditions or site specific variation could have affected these results. We also were following recommendations on the methodology of surveying from previous butterfly surveys (Debinski et al. 2000), but for a park of this size we would recommend increasing the length of transects from 50 m to 300 m and walking each transect only once. Increasing the length of transects would allow a greater range of topography to be sampled at each location which can influence both plant communities (Grace et al. 2000) and butterfly activity (Fleishman and MacNally 2002). Longer transects could also buffer against artificially increased diversities due to re-sampling hot spots of butterfly activity. By walking each transect once instead of multiple times, more transects could be surveyed by removing the waiting time between repeating samples of transects. Additionally, multiple walks of the same transect likely result in recounting many individuals repeatedly, which can complicate the analyses. It could also be useful to compare the butterfly diversity of each transect to the diversity of herbaceous flowering plants along the transects to correlate butterflies to available food resources. With the large number and diversity of butterflies and the larger abundance of prairie specialists supported, the patch-burn grazing system is likely an important strategy for the continued success of butterflies on the TAPR. The rotating burn provides the heterogeneity of habitats needed for the continued success of many of the butterfly species that are not commonly found in the traditional annual burned and intensively grazed pastures. With the propensity of butterflies to be used as indicator species (Kerr et al. 2000) and evidence of other species intolerance of annual burned IES pastures (Robbins et al. 2002), it is likely that many other clades will also benefit from the patch-burn grazing system. As such, the TAPR is likely an important refuge for prairie obligate and generalist species alike. It will be important to continue monitoring programs for butterflies and all other taxa utilizing this area to ensure the continued benefits of the grazing strategy

10 Acknowledgments Project funding was provided by the National Park Service, NRPP Regional Program Block Allocations. Thanks go to Jesse Murray who helped us survey for butterflies on several occasions. We are indebted to Paula Matile, Flint Hills Conservation Specialist with The Nature Conservancy for help with various aspects of this project, but especially for preparing the maps included in this final project report. We also thank Kristen Hase, Chief of Natural Resources at TAPR from the National Park Service, for help obtaining this contract and many other aspects of this project

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13 Moffat, M., and N. McPhillips Management for butterflies in the northern Great Plains: a literature review and guidebook for land managers. U.S. Fish and Wildlife Service, Pierre, South Dakota. 19 pp. Natuhara, Y., C. Iman, and M. Takahashi Evaluation of community indices in seasonal assemblages of butterflies (Lepidoptera) at different frequencies of transect count. Biodiversity and Conservation 7: Panzer, R., D. Stillwaugh, R. Gnaedinger, and G. Derkovitz Prevalence of remnant dependence among prairie and savanna inhabiting insects of the Chicago region. Natural Areas Journal 15: Pollard, E., and T. J. Yates Monitoring butterflies for ecology and conservation. London: Chapman & Hall. Poyry, J., S. Lindgren, J. Salminen, and M. Kuussaari Responses of butterfly and moth species to restored cattle grazing in semi-natural grasslands. Biological Conservation 122: Powell, A. N Grassland bird inventory of seven prairie parks. Final report to the Great Plains Prairie Cluster Long-term Ecological Monitoring Program, National Park Service, Wilson s Creek National Battlefield, Republic, Missouri. 47 p. Pyle, R., M. Bentzien, and P. Opler Insect conservation. Annual Review of Entomology 26: Pywell, R. F., E. A. Warman, T. H. Sparks, J. N. Greatorex-Davies, K. J. Walker, W. R. Meek, C. Carvell, S. Petit, and L. G. Firbank Assessing habitat quality for butterflies on intensively managed arable farmland. Biological Conservation 118: Robbins, M.B., A. T. Peterson, and M.A. Ortega-Huerta Major Negative Impacts of Early Intensive Cattle Stocking on Tallgrass Prairies: The Case of the Greater Prairie-Chicken (Tympanuchus cupido). North American Birds 56: Samson, F.B., and F.L. Knopf Prairie conservation in North America. Bioscience 44:

14 Samways, M. J Insect Conservation Biology. Chapman & Hall, London. Samways, M. J., S. Taylor, and W. Tarboton Extinction reprieve following alien removal. Conservation Biology 19: Scoble, J. J The Lepidoptera: Form, Function and Diversity. Oxford University Press, New York. Simonson, S. E., P. A. Opler, T. J. Stohlgren, and G. W. Chong Rapid assessment of butterfly diversity in a montane landscape. Biodiversity and Conservation 10: Swengel, A.B Monitoring butterfly populations using the Fourth of July butterfly count. American Naturalist 124: Spizter, K, J. Jaros, J. Havelka, and J. Leps Effect of small-scale disturbance on butterfly communities of an Indochinese montane rainforest. Biological Conservation 80:9-15. Swengel, A.B Monitoring butterfly populations using the Fourth of July butterfly count. American Naturalist 124: Swengel, A Regal fritillary: prairie royalty. American Butterflies 1:49. Swengel, A. B Effects of fire and hay management on abundance of prairie butterflies. Biological conservation 76: Swengel, A. B A literature review of insect responses to fire, compared to other conservation managements of open habitat. Biodiversity and Conservation 10: Wasson, T., L. Yasui, K. Brunson, S. Amend, V. Ebert A Future for Kansas Wildlife, Kansas' Comprehensive Wildlife Conservation Strategy. Dynamic Solutions, Inc. in cooperation with Kansas Department of Wildlife and Parks.170 pp

15 Figure 1. The four burn management units at the TAPR where butterfly transects were located

16 Figure 2. Big pasture at the TAPR showing the 3-year patch-burn units and butterfly transect sites

17 Figure 3. Two Section Pasture at the TAPR showing the butterfly transect sites. This pasture is under traditional management where it is intensively stocked with cattle after an annual burn

18 Table 1. Cumulative list of butterflies observed during 2010 summer surveys at the TAPR. The total number of butterflies observed in each of the four burn treatments (2008, 2009, 2010 and traditional) is indicated, an X indicates the species was observed in the treatment but not during a transect survey. Additionally, monthly trips were also taken to a natural prairie stream (Palmer Creek) in the park and butterfly species that were only observed here are also indicated by an X. Species Traditional Great Spangled Fritillary X X 0 0 Speyeria cybele Regal Fritillary Speyeria idalia Variegated Fritillary Euptoieta claudia American Lady X Vanessa virginiensis Buckeye X Junonia coenia Eastern Comma Polygonia comma Monarch Danaus plexippus Mourning Cloak 0 X 0 0 Nymphalis antiopa Painted Lady Vanessa cardui Pearl Crescent Phyciodes tharos Question Mark Polygonia interrogationis Red Admiral X Vanessa atalanta Red-Spotted Purple X Limenitis arthemis astyanax Silvery Checkerspot X Chlosyne nycteis Viceroy Limenitis archippus Palmer Creek X X

19 Little Wood Satyr Megisto cymela Northern Pearly-Eye Enodia anthedon Wood Nymph Cercyonis pegala Gray Hairstreak Strymon melinus Juniper Hairstreak Callophrys gryneus Reakirt's Blue Hemiargus isola Spring/Summer Azure Celastrina neglecta Eastern Tailed-Blue Everes comyntas Gray Copper X Lycaena dione Cabbage White Pieris rapae Checkered White 1 X 0 1 Pontia protodice Clouded Sulphur Colias philodice Cloudless Sulphur Phoebis sennae Dainty Sulphur 0 1 X 0 Nathalis iole Little Yellow Eurema lisa Orange Sulphur X Colias eurytheme Sleepy Orange Eurema nicippe Southern Dogface Colias cesonia Black Swallowtail Papilio polyxenes Giant Swallowtail Papilio cresphontes X X X X X X

20 Eastern Tiger Swallowtail Papilio glaucus Zebra Swallowtail 0 X 0 0 Eurytides marcellus Arogos Skipper Atrytone arogos Checkered-Skipper Pyrgus communis Crossline Skipper 0 6 X X Polites origenes Dun Skipper Euphyes vestris Eufala Skipper Lerodea eufala Fiery Skipper Hylephila phyleus Least Skipper 0 X 0 0 Ancyloxypha numitor Ottoe Skipper Hesperia ottoe Sachem X Atalopedes campestris Silver-Spotted Skipper Epargyreus clarus Tawny-Edged Skipper Polites themistocles Southern Cloudywing X Thorybes bathyllus Horace's Duskywing Erynnis horatius Wild Indigo Duskywing Erynnis baptisiae X X

21 Table 2. Mean butterfly diversity ± SD (Simpson Diversity Index) for each month in each of the four burn treatments. Burn May June July August September Treatment Diversity Diversity Diversity Diversity Diversity Traditional 1.23 ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ±

22 Figure 4. Mean butterfly diversity ± SD (Simpson Diversity Index) by month during the summer of 2010 on the TAPR

23 Figure 5. Mean butterfly diversity ± SD (Simpson Diversity Index) by burn treatment during the summer of 2010 on the TAPR

24 Table 3. Species of possible occurrence on the TAPR (Dole et al., 2004). Hackberry Emperor Tawny Emperor Pipevine Swallowtail Olympia Marble Mexican Yellow Harvester Bronze Copper Coral Hairstreak Soapberry Hairstreak Banded Hairstreak Henry's Elfin Red-banded Hairstreak Texan Crescent Bordered Patch Gorgone Checkerspot Phaon Crescent Goatweed Leafwing Queen Hayhurst's Scallopwing Zebulon Skipper Nysa Roadside-Skipper Common Roadside-Skipper Bell's Roadside-Skipper Delaware Skipper Asterocampa celtis Asterocampa clyton Battus philenor Euchloe olympia Eurema mexicana Feniseca tarquinius Lycaena hyllus Satyrium titus Phaeostrymon alcestis Satryium calanus Callophrys henrici Claycopis cecrops Phyciodes texana Chlosyne lacinia Chlosyne gorgone Phyclodes phaon Anaea andria Danaus gilippus Staphylus hayhurstii Poanes zabulon Amblyscirtes nysa Amblyscirtes vialis Amblyscirtes belli Anatrytone logan