1. The Effect of Grazing on the Spatial Heterogeneity of Vegetation
Adler, P.B., Raff, D., and Lauenroth, W. 2001. Oecologia 128(4):465-479
This study suggests grazing alters the spatial heterogeneity of vegetation, creating a patchy pasture mosaic which in turn increases ecosystem function. This study attempts to model how and why grazing increases or decreases spatial heterogeneity. The study finds continuous and no grazing decreases heterogeneity while intermediate grazing increases heterogeneity. The study also indicates landscape attributes, such as shade pools and watering stations that constrain grazing frequency, intensity, and duration also increases spatial heterogeneity. In conclusion, how often a patch is grazed determines spatial heterogeneity of vegetation, but how often a site is gazed is determined by landscape patterns.
2. Plant Species Diversity and Grazing in the Scandinavian Mountains – Patterns and Processes at Different Spatial Scales
Austrheim, G., and Eriksson, O. (2001). Ecography, 24(6), 683-695
There is a long tradition of grazing semi-domestic reindeer and sheep in alpine and sub-alpine Scandinavian habitats. Current conservation ideology calls into question the practice of grazing and instead recommends grazing exclusion. This paper suggests the high plant diversity associated in Scandinavian mountain meadows is the result of humans grazing animals for thousands of years. The author concludes grazing is a key process for maintaining biodiversity in the Scandinavian mountains, and the practice of grazing needs to continue.
3. Farmland Biodiversity: Is Habitat Heterogeneity Key?
Benton, T.G., Vickery, J.A., and Wilson, J.D. 2003. Trends in Ecology & Evolution 18(4):182-188
This study examines the literature concerning agricultural intensification and the widespread decline in farmland biodiversity in temperate agricultural regions. The authors conclude the loss of ecological heterogeneity is a universal consequence of agricultural intensification. The author concludes that attempts to reverse declines in farmland biological diversity will include policy frameworks that benefit both the producer and biodiversity.
4. Establishing Grazing and Grazing-Excluded Patches Increases Plant and Invertebrate Diversity in a Mediterranean Oak Woodland
Bugalho, M. N., Lecomte, X., Goncalves, M., Caldeira, M. C., and Branco, M. 2011. Forest Ecology and Management, 261(11), 2133-2139
Grazing is an important ecological process in Mediterranean ecosystems but, there is little information about grazing impacts on biodiversity. This study conducts an experiment to assess the impacts of grazing and grazing-exclusion on plant and invertebrate diversity in a Mediterranean evergreen oak woodland. While total diversity between the two treatments did not differ, the floristic composition between the two treatments differed significantly. Some plant species and invertebrate taxa were recorded exclusively in grazed or ungrazed plots. Management practices that maintain grazing and small scale grazing-excluded areas can increase habitat heterogeneity and promote plant and invertebrate diversity.
5. Effects of Rotational Grazing on Nesting Ducks in California
Carroll, L.C., Arnold, T.W., and Beam J.A. 2007. The Journal of Wildlife Management 71(3):902-905
This study challenges the current narrative concerning the detrimental impacts of grazing on waterfowl production. Duck nest success is compared between grazed and un-grazed units for two seasons in Central California. Results conclude no difference in duck nest survival between graze and un-graze units. In certain circumstances, grazing may enhance waterfowl production by creating corridors that allow newly hatched upland nesting waterfowl more efficient access to open water. Likewise, herbivore dung piles attract insects which serve as a key food component to young and molting waterfowl. The authors conclude grazing should be considered as a management procedure on Federal, State, and private waterfowl production lands.
6. Effects of Patch-burn Management on Dickcissel Nest Success in a Tallgrass Prairie
Churchwell, R. T., Davis, C. A., Fuhlendorf, S. D., and Engle, D. M. (2008). Journal of Wildlife Management, 72(7), 1596-1604.
Grassland bird populations have declined more dramatically than any other North American bird community. Grassland birds evolved within heterogeneous patchy biotic communities structured through interactions between fire and grazing. Current grassland management diminishes this patchiness while favoring homogenous biotic communities. For example, continuous grazing promotes homogeneous stands of short vegetation, while “natural” area management such as Conservation Reserve, favors homogenous stands of tall vegetation. The authors suggest management which promotes homogenous biotic communities at the expense of patchiness might be responsible for declines in grassland bird populations. The authors examine the impacts of burning and grazing (patch burn grazing) verses traditional management (annual burning or continuous grazing) on the reproductive success of the grassland bird dickcissels (Spiza americana) in tallgrass prairie in Oklahoma. Dickcissel nest success was higher in patch-burn grazed units than in traditional management units. The positive response of dickcissel nest success to patch-burn management provides further evidence that patch burn grazing offers a useful tool for grassland bird conservation and should be encouraged as a conservation strategy for grassland bird conservation.
7. Effects of Fire, Grazing and Topographic Variation on Vegetation Structure in Tallgrass Prairie
Collins, S. L., and Calabrese, L. B. (2012). Journal of Vegetation Science, 23(3), 563-575
This study identifies the impacts on plant diversity following 20 of years burning and 13 years of bison grazing. Results indicate species diversity is maximized in sites infrequently burned and grazed, while diversity was lowest on frequently burned and ungrazed sites. In general, grass cover was highest in infrequently burned ungrazed sites and lowest on frequently burned grazed sites, while forb richness was highest in infrequently burned and grazed sites. Frequent burning favored C4 grasses, which reduced the abundance of C3 forbs. Responses of dominant grasses and forbs to fire and grazing varied depending on topographic position. Community stability was positively correlated with species richness. The authors conclude a combination of bison grazing and periodic fire is necessary to maximize diversity and community stability.
8. Avian Community Response to Vegetation and Structural Features in Grasslands Managed with Fire and Grazing
Coppedge, B.R., S.D. Fuhlendorf, W.C. Harrell and Engle D.M. 2008. Biological Conservation 141:1196-1203
This study compares bird communities between grazed and un-grazed, burned and unburned grasslands from 2001 to 2003 in Oklahoma. Bird diversity is higher in burned and grazed units at various stages of succession and lowest in units not grazed and not burned. Managers interested in grassland bird communities are encouraged to consider patch burn grazing management to increase both bird diversity and palatable forage. This study also examines the role of manmade structures, such as roads, stock-ponds and shelter-belts on bird community composition, and concludes pasture management to increase landscape heterogeneity in terms of vegetation and structure, correlates to increases bird diversity
9. The Presence of Sheep Leads to Increases in Plant Diversity and Reductions in the Impact of Deer on Heather
DeGabriel, J. L., Albon, S. D., Fielding, D. A., Riach, D. J., Westaway, S., and Irvine, R. J. (2011). Journal of Applied Ecology, 48(5), 1269-1277
Management of grazing herbivores is an important tool for maintaining biodiversity in many ecosystems. Mixed grazing by sheep and deer appears beneficial for increasing diversity and minimizing damage to heather in the uplands. Results indicate that reducing livestock may alter the impacts of wild grazers on their habitats and drive changes in diversity, whereas mixed grazing can enhance habitat quality and maintain plant diversity.
10. Livestock as Ecosystem Engineers for Grassland Bird Habitat in the Western Great Plains of North America
Derner, J.D., W.K. Lauenroth, P. Stapp and D.J. Augustine. 2009. Rangeland Ecology & Management 62(2):111-118
This study examines the potential for livestock to act as “ecological engineers” to achieve desired habitat modification for declining grassland bird populations. The research concludes using livestock as ecosystem engineers to modify vegetation is feasible and more research on using livestock to achieve desired grassland bird habitat in relationship to financial feasibility on public and private lands should be conducted.
11. Effect of Cattle Grazing a Species-Rich Mountain Pasture under Different Stocking Rates on the Dynamics of Diet Selection and Sward Structure
Dumont, B., Garel, J. P., Ginane, C., Decuq, F., Farruggia, A., Pradel, P. (2007). Animal, 1(7), 1042-1052
Stocking rate is a key management variable influencing the structure and composition of pastures. Few studies analyzed seasonal patterns of pasture use. This study examines 3 different stocking rates over 3 years. Data included diet selection, plot use, and impact on sward structure and quality in a species-rich mountain pasture of central France. Heifers selected for legumes & forbs, and against reproductive grass whatever the stocking rate or season. Neither diet quality nor individual animal performance was affected by the stocking rates. Sward heterogeneity was highest in moderately grazed plots, suggesting a potential optimal balance between livestock production and conservation management.
12. Restoring Heterogeneity on Rangelands: Ecosystem Management Based on Evolutionary Grazing Patterns. 2001
Fuhlendorf, S.D. and Engle D.M.. 2001. BioScience 51(8):625-632
This paper proposes a pasture paradigm to enhance diversity instead of homogeneity on rangelands grazed by livestock. The concept implied is called “patch-burn grazing” and is designed to mimic historic interactions between fire and large herbivores. The two disturbances, fire and grazing are constrained by time and edaphic attributes to create a landscape patchiness of shifting biotic communities that enhance biodiversity, productivity, and ecosystem function. The authors suggest patch burn grazing replace the current “uniform disturbance” pasture management narrative in areas with multiple objectives such as biodiversity and agricultural production.
13. Application of the Fire—Grazing Interaction to Restore a Shifting Mosaic on Tallgrass Prairie
Fuhlendorf, S.D., D.M. Engle. 2004. Journal of Applied Ecology 41(4):604-614
This paper explores feedbacks between fire and grazing that creates a shifting vegetative mosaic that increases biodiversity, productivity, and ecosystem function in Oklahoma grasslands. This research attempts to restore a historic disturbance regime, where landscape patterns influence fire intensities and subsequently grazing intensities. Results show patch-burn grazing management increases community heterogeneity, biodiversity, productivity and ecosystem function. The authors suggests patch-burn grazing be employed on lands seeking to satisfy biodiversity and agricultural production objectives.
14. Should Heterogeneity be the Basis for Conservation? Grassland Bird Response to Fire and Grazing
Fuhlendorf, S.D., Harrell, W.C., Engle, D.M., Hamilton, R.G., Davis, C.A., Leslie, D.M. Jr. 2006. Ecological Applications 16(5):1706-1716.
This paper examines the effects of “patch-burn grazing” on grassland bird diversity in tallgrass prairie. The results indicate different plant species associate with different intensities of fire and grazing and different bird species correspond with different vegetation. Some plant and bird species show a preference to intensely burned and grazed treatments, while other plant and bird species show preference to infrequently burned and grazed treatments, and still other plant and bird species seem to prefer in-between intensities of fire and herbivory. The authors conclude that agricultural (i.e. grazing) and ecological objectives (i.e. bird diversity) can be achieved through management strategies that mimic historic shifting disturbance regimes that include both fire and herbivory.
15. Pyric Herbivory: Rewilding Landscapes Through the Recoupling of Fire and Grazing
Fuhlendorf, S. D., Engle, D. M., Kerby, J., Hamilton, R. (2009). Conservation Biology, 23(3), 588-598
This study examines the relationship between fire and grazing over time and space. The authors conclude the ecological interaction of fire and grazing are dependent opon one another and over time, create a shifting mosaic were community patches vary in composition depending upon the time since the last fire and or grazing event occurred. The authors call this process pyric herbivory and conclude grazing and fire through a series of positive and negative feedbacks establish a predictable burning-grazing pattern on the landscape.
16. Effects of Bison Grazing, Fire, and Topography on Floristic Diversity in Tallgrass Prairie
Hartnett, D., Hickman, K., Walter, L. (1996). Journal of Range Management, 49(5), 413-420
The authors sample plant diversity on grazed and ungrazed sites subjected to different fire frequencies in the Konza Prairie in northeast Kansas. The objective was to determine the effects of bison grazing on plant community composition in sites with contrasting fire frequencies. The study found some plant species increased and some species decreased with grazing. Total diversity was significantly higher in grazed sites versus ungrazed sites. Increases in plant diversity associated with bison grazing were greater in annually burned than occasionally burned sites.
17. Diversity and Invasion: Implications for Conservation
Hobbs, R.J. L.F. Huenneke. 1992. Conservation Biology 6(3):324-337
This paper summarizes how different disturbance regimes (i.e. fire, grazing, soil disturbance, and nutrient additions) affect plant diversity. Disturbance regimes that closely mimic historic disturbance regimes tend to maintain intact functional diverse ecosystems. Likewise, disturbance regimes that differ from historic regimes, including type of disturbance, intensity, frequency and duration can decrease ecosystem integrity, function, and diversity. Ecosystems outside historic disturbance patterns are vulnerable to invasion by undesirable species and subsequent rapid transitions from functional to dysfunctional ecosystems.
18. Grazers, browsers, and Fire Influence the Extent and Spatial Pattern of Tree Cover in the Serengeti
Holdo, R. M., Holt, R. D., Fryxell, J. M. (2009). Ecological Applications, 19(1), 95-109
African savanna acts as a model to help us better understand how savanna intentionally ecosystems functioned prior to intensive antropocation. Some argue African savannas are different than temperate savannas of North America and Eurasia; however, both systems are adapted to predictable seasonal climates: African systems senesce during hot dry periods, temperate savannas senesce during cold dry periods, and animals in both systems adjust their movements accordingly. This study develops a dynamic simulation model to better understand feedbacks between vegetation, fire, and herbivores. Results show grazers in open migratory ecosystems, can regulate the impact of fire and thus exert strong controls on landscape tree patterns.
19. Herbivore-induced Coexistence of Competing Plant Species
Ishii, R., Crawley, M. J. (2011). Journal of Theoretical Biology, 268(1), 50-61
This paper uses a lottery model to understand feedbacks between two competing plant species, one palatable and the other non-palatable, in a homogeneous habitat grazed by large herbivores. The non-palatable species suffers from low reproductive success due to trade-offs for being non-palatable. Coexistence of the two plants cannot occur when the herbivore density is very low; the palatable plant always wins, or when the herbivore density is very high; the non-palatable plant always wins. Intermediate herbivore densities facilitate plant coexistence, even in a homogeneous environment. Herbivore forage-selection depends on average palatability and both plant populations are stabilized and coexistence is promoted. The authors conclude biodiversity objectives in grasslands are dependent on herbivore identity, density, duration and frequency.
20. Direct and Indirect Effects of Livestock Grazing Intensity on Processes Regulating Grassland Bird Populations
Johnson, T.N. 2011. Dissertation.
This dissertation examines impacts of grazing intensity on vegetation structure and grassland songbird demography in a Northwest USA bunch-grass prairie. Different treatments receive different intensities of grazing. Results show songbird diversity does not change between grazing intensity, but songbird community composition differs significantly between treatments. This suggests different songbird species prefer different vegetation structure resulting from different grazing intensities. The research also identifies changes in songbird food (i.e. insects) quality, with declines in heavily grazed paddocks leading to nesting failures. The research concludes by suggesting good grazing management can maintain diverse grassland bird populations and agriculture production.
21. Restoring Tallgrass Prairie and Grassland Bird Populations in Tall Fescue Pastures with Winter Grazing.
Johnson, T.N. Sandercock, B.K. 2010. Rangeland Ecology & Management 63(6):679-688.
This paper examines the potential to use grazing as a tool to restore warm season prairie plant species and how this might impact grassland bird communities. Experimental pastures are dominated by tall fescue (Schedonorus phoenix), a cool season exotic grass species. Treatments include: 1) grazing livestock year around so both cool and warm season species are defoliated and 2) grazing livestock only during the cool season so only the cool season species are defoliated. The experiment runs for five years. Results show cool season grazing significantly increases warm season prairie plant species dominance. Bird species respond differently; some species prefer continuous grazing while other species benefit from seasonal grazing. The author concludes that grazing and cessation of fertilizer can provide an effective restoration tool for rangeland with objectives for both agriculture production and biodiversity.
22. Grazing Impact on Plant Spatial Distribution and Community Composition
Kohyani, P. T., Bossuyt, B., Bonte, D., Hoffmann, M. (2011). Plant Ecology and Evolution, 144(1), 19-28
Land managers are increasingly interested in using grazing animals to help conserve the few remaining natural grasslands. In theory, grazing livestock helps prevent invasion and dominance by late successional low-quality plant species (i.e. plants which provide few ecosystem services such as food and fiber production, soil building, water infiltration and purification, and nutrient regulation). This study tests the effects of herbivores to reduce dominance by late successional low-quality species. Results indicate grazing is effective at reducing community dominance by late successional low-quality species while at the same time facilitating the emergent of less competitive high-quality plant species, and increasing total biological diversity.
23. How much does Grazing-induced Heterogeneity Impact Plant Diversity in Wet Grasslands?
Marion, B., Bonis, A., Bouzille, J. (2010). Ecoscience, 17(3), 229-239
While much research exists indicating the positive impacts of grazing on grassland heterogeneity and biodiversity in plant communities, the mechanisms linked to this relationship remain unclear. This study examines 3 different wet-grassland communities situated along the French Atlantic that have been historically grazed by horses and cattle. Results show a positive correlation between grazing, patchiness, and species richness. The authors conclude grazing-induced patchiness entirely explained the increase in plant richness, and partially explained the recruitment of new species.
24. Rabbit Grazing as the Major Source of Intercanopy Heterogeneity in a Juniper Shrubland
Marko, G., Onodi, G., Kertesz, M., Altbaecker, V. (2011). Arid Land Research and Management, 25(2), 176-193
Semi-arid shrublands are fire dependent communities; however, in recent time fire within these communities has increasingly become catastrophic: dense grass-shrub vegetation ignites, blows-up, and then spreads uncontrollably. Shrubs are more prone to ignition when intercanopy vegetation accumulates and contributes to excessive fuel loads. This study occurs in a semi-arid shrub community prone to high fire risk, where grass density under red cedars contributes high loads. The authors examine the relative significance of 3 main factors contributing to intercanopy plant cover and fuel loads including: allelopathy, shading, and herbivory. Test plots either contained or excluded grazing rabbits. Results indicate that neither shading nor allelopathy are as important as herbivory for reducing plant cover and fuel loads. The authors conclude local herbivore activity can affect the spatial heterogeneity of combustible materials, and moderate rabbit grazing can reduce catastrophic fire.
25. Long-term Impacts of Extensive Grazing and Abandonment on the Species Composition, Richness, Diversity and Productivity of Agricultural Grassland
Marriot, C.A., K. Hood, J.M. Fisher and R.J. Pakeman. 2009. Agriculture, Ecosystems & Environment 134(3-4):190-200
This paper examines the effectiveness of grassland extensification on addressing declines in biodiversity in agricultural landscapes. The study compares productivity, diversity, and species composition between grazed and ungrazed grasslands. Results indicate good grazing can maintain productivity, increase biodiversity, and maintain desirable species composition. Abandoned land shows no decline in biodiversity, but does show a significant change in species composition, with a trend towards rank low-quality weedy species, suggesting proper grazing promotes high quality vegetation.
26. Disturbance Response in Vegetation Towards a Global Perspective on Functional Traits
McIntyre, S., Lavorel, S., Landsberg, J., and T. Forbes. (1999). Journal of Vegetation Science, 10(5), 621-630
Functional trait analysis of plant communities provides an informative description as to why certain species inhabit a particular space in a particular time. Plants with similar functional traits inhabit similar environmental spaces. Functional trait diversity provides a more useful approach to quantifying biodiversity and is commonly employed in Europe and Australia, but has failed to gain acceptance in North America. This paper attempts to categorize plant species into functional groups based on their resilience to various grazing intensities. Increases in functional diversity, which equates to increases in ecosystem function and service, theoretically occurs in paddocks subjected to intermediate intensities of grazing at predictable times. The authors identify 3 functional groups tolerant to three intensities of grazing pressure and include: heavy, moderate, and low grazing groups, in both cool and warm seasons. The authors conclude functional trait analysis should provide explicit descriptions of evolutionary and ecological traits from a global perspective.
27. Spatial Heterogeneity and Plant Species Richness at Different Spatial Scales Under Rabbit Grazing
Olofsson, J., de Mazancourt, C., & Crawley, M.J. 2008. Oecologia (2008) 156:825–834
This paper documents increases in spatial heterogeneity and species richness in a rabbit-grazed grassland. The research examines the relationship between spatial patterns of grazing intensity, rabbit droppings, plant height, plant biomass, soil water, and nutrient cycling in grazed and ungrazed treatments in southern England grasslands. Results indicate rabbit grazed sites contain 2 different plant assemblages: 1) heavily grazed patches with low vegetation (lawns) with high nutrient soils, and 2) ungrazed patches with high vegetation and nutrient-poor soils (tussocks). Rabbit grazing increases species richness at all spatial scales. Species richness was negatively correlated with plant height and positively correlated with diverse vegetation height, both low and high vegetation.
28. Different Grazing Strategies are Necessary to Conserve Endangered Grassland Birds in Short and Tall Salty Grasslands of the Flooding Pampas
Pablo Isacch, J., and Augusto Cardoni, D. (2011). Condor, 113(4), 724-734
This study examines how grazing affects bird assemblages in coastal salt-grasslands in Argentina. Four different types of grazing (rotational, continuous, winter grazing, and graze exclusions) are examined. Results show different species of birds prefer different types of grazing. The authors propose diverse avian communities will require a system of heterogeneous grazing systems that optimizes both agri-production and conservation of grassland birds.
29. Comparison of Riparian Plant Communities under Four Land Management Systems in Southwestern Wisconsin
Paine, L.K., Ribic, C.A. 2002. Agriculture, Ecosystems & Environment 92(1):93-105
This study compares riparian plant communities under four types of management: 1) continuous grazing, 2) rotational grazing, 3) woody buffer strip, and 4) grassed buffer strip. Results indicate plant diversity is highest in woody buffer strip, rotational, and continuous grazing management regimes. Less desirable species, such as reed canary grass, display higher dominance in grassed and woody buffer strips, and are nearly absent in continuous and rotational grazing treatments. Native plant species display a higher frequency in both rotational and continuous grazing units. The authors conclude well managed grazing can achieve both agricultural production and ecosystem integrity objectives.
30. Another Tool in the Toolbox? Using Fire and Grazing to Promote Bird Diversity in Highly Fragmented Landscapes.
Pillsbury, F.C., Miller, J.R., Debinski, D.M., & Engle, D.M. 2011. Ecosphere 2(3):Article 28
Patch-burn grazing (PBG) can increase grassland bird biodiversity in extensive grassland landscapes (i.e. landscapes dominated by un-fragmented grasslands); however the ability for PBG to amplify grassland bird diversity in fragmented landscapes (i.e. landscapes dominated by annual crops) is not understood. This study indicates restoration of diverse grassland bird communities in fragmented landscapes are less dependent on employment of PBG and more dependent on landscape context. The authors suggest restoration of diverse grassland bird communities in fragmented landscapes requires a reversal in fragmentation first and implementation of PBG second.
31. Grassland Bird Responses to Land Management in the Largest Remaining Tallgrass Prairie
Rahmig, C.J., Jensen W.E., & With, K.A. 2009. Conservation Biology 23(2):420-432
This paper examines impacts of grazing on grassland bird community composition in the Flint Hills of Kansas. Bird surveys occur in grazed, hayed, and CRP treatments. Results indicate the lowest bird diversity is correlated with CRP fields and different bird species prefer different management techniques. The author concludes diversification of land management, to include grazing, burning, resting, and haying would serve best to restore diverse grassland bird communities in the Flint Hills landscape.
32. Grassland Birds Associated with Agricultural Riparian Practices in Southwestern Wisconsin
Renfrew, R.B., Ribic C.A. 2001. Journal of Range Management 54(5):546-552
This paper examines four common types of land management impacts on bird diversity in riparian landscapes in Southwest, Wisconsin. The four types of land management include: 1) row crop production, 2) rotational grazing, 3) continuous grazing, and 4) grassed buffer strips. Results show no difference between bird diversity between land use types; however, bird species of management concerns are found more frequently in both grazing types, rotational and continuous continuous and rotational, but rarely in buffer strip and row crop land management types. The authors conclude different types of bird species prefer different types of vegetation associated with different types of land management.
33. The Influence of Grazing Intensity and Landscape Composition on the Diversity and Abundance of Flower-visiting Insects
Sjodin, N.E., Bengtsson, J., Ekbom, B. 2008. Journal of Applied Ecology 45(3):763-772
This study compares insect pollinator diversity under three different grazing intensities:
- moderate grazing
- intense grazing in both extensive and fragmented landscapes
Results seem to indicate different types of pollinators prefer different grazing intensities; however, how different grazing intensities are arranged on the landscape seems more important to pollinator diversity then just different grazing intensities. The authors suggest grazing plans to encourage insect pollinator diversity should be developed at the landscape context and not for the individual pasture.
34. Feedback Loops in Ecological Hierarchies Following Urine Deposition in Tallgrass Prairie
Steinauer, E., & Collins, S. (2001). Ecology, 82(5), 1319-1329
Ecologists often predict large-scale factors constrain small-scale factors, but the potential for small-scale events to impact large-scale structure is unclear. This study examines the effects of highly localized urine deposition on large-scale vegetation structure and composition in tallgrass prairie, and if urine deposition, plant community response, and grazing are related to one another through a series of feedbacks. Results indicate bison grazing was more intense on urine patches than off urine patches. Also, grazed patches on urine deposition sites expanded well beyond the area of urine deposition. The combination of urine patches plus grazing produced unique large-scale vegetation patches. Bison preferentially grazed urine patches, which eventually became “grazing lawns” that in turn attracted more grazing, thus establishing a positive feedback loop. The authors conclude urine patches are an example of a small-scale disturbance that constrains large-scale patch structure in tallgrass prairie. While this study identifies a unique positive feedback between urine deposition and grazing, the conclusion suggesting a small scale disturbance of urine patches constrains large scale vegetation patterns fails to consider herd movement is constrained by landscape features such as river crossings, saddles, shade pools, canyons, and etc. The landscape context allows us to understand how grazing animals choose preferential grazing lawns. In this case a “larger” feature, the landscape, constrains a smaller feature, urine patches.
35. The Relative Importance of Grazing Stock Type and Grazing Intensity for Conservation of Mesotrophic ‘Old Meadow’ Pasture
Stewart, G.B. and A.S. Pullin. 2008. Journal for Nature Conservation 16(3):175-185
This study examines the potential of grazing livestock to maintain rare grassland communities in Britain that are threatened by conversion into row crop production and “improved” pasture. The authors conduct a literature review to conclude a significant lack of research makes it difficult to draw any general conclusions as to which type of livestock will achieve optimal conservation objectives. The only discernible pattern occurs between grazing intensity and vegetation composition where the evidence suggests intermediate grazing maximizes species richness. The authors suggest future research collect more accurate data on grazing intensities by different types of livestock in relationship to plant community composition.
36. Vegetation Trends in Tallgrass Prairie from Bison and Cattle Grazing
Towne, E., Hartnett, D., Cochran, R. 2005. Ecological Applications, 15(5), 1550-1559
This paper summarizes a 10-year study to compare the differences in vegetation change between cattle and bison grazed treatments in a Kansas, USA tallgrass prairie. All treatments were burned and grazed and stocking rates were considered moderate. Grazing pressure was held constant by matching animal body mass in all pastures each year. Results show bison and cattle differentially modify vegetation composition and structure, but overall, plant communities in bison and cattle pastures were 85% similar after 10 years. The authors conclude measurable differences between cattle and bison-grazed pastures in tallgrass prairie are typically in response to contributing factors, such as stocking rates, frequencies, intensity and duration rather than differences between herbivore species.
37. Influence of Grazing and Fire Frequency on Small-scale Plant Community Structure and Resource Variability in Native Tallgrass Prairie
Veen, G. F., Blair, J. M., Smith, M. D., Collins, S. L. 2008. Oikos, 117(6), 859-866.
Grazing and fire are important forces affecting resource availability and plant community composition. It is not clear whether changes in community structure are the effects of disturbance (i.e. grazing and fire) or the indirect effects brought about by changes in resource availability (i.e. nutrients and sunlight). This research conducts a field study to determine the effects of long-term fire and grazing regimes by bison on plant community structure and resource variability. Results show grazing increased light and nitrogen availability, reduced C-4 grass dominance, and increased species richness, diversity and heterogeneity. In contrast, annual fire increased C-4 grass dominance and decreased species richness and diversity, particularly in absence of grazing, but had no effect resource availability. The authors conclude the direct impacts of grazing and fire had more impact on community composition and structure than did the indirect effects of resource availability. The author’s conclusion is justified; however, it depends on the temporal and spatial scale we choose to observe the system. If we change scale, the dominant set of controls over community composition and structure, fire and grazing in this case, switch and resource availability becomes the constraining factor over plant community composition and structure.
38. Diet Selection Variation of a Large Herbivore in a Feeding Experiment with Increasing Species Numbers and Different Plant Functional Group Combinations
Wang, L., Wang, D., Liu, J., Huang, Y., & Hodgkinson, K. C. 2011. Acta Oecologica-International Journal of Ecology, 37(3), 263-268
This study exams the impact of sheep grazing on plant functional diversity (e.g. plant guilds such as: spring ephemeral, cool season, warm season, graminoid herbaceous and so forth). The authors assume good grazing management can maintain high levels of plant functional diversity, but this research examines the role of plant functional diversity’s influence on grazing patterns. The experiment exposes sheep to increasingly higher levels of plant functional diversity. Results show preferential grazing declines as plant biodiversity increases, indicating a negative feedback between selectivity and diversity. In conclusion, the authors suggest that high levels of biodiversity tend to decrease selectivity by sheep while promoting uniform utilization of pasture which in turn reinforces a high level of diversity.
39. Megaherbivores and Southern Appalachian Grass Balds
Weigl, P., & Knowles, T. (1995). Growth and Change, 26(3), 365-382
This study examines the persistence of high altitude treeless grass “balds” in the Southern Appalachians. The balds are historically described in both the Amerindian oral tradition and early accounts by early European settlers. Modernization of agriculture led to the abandonment of the balds, and subsequently, the balds are rapidly transitioning from open meadows into closed woodland. Despite the assemblage of rare and unique plants, the balds receive little conservation attention because they are considered a human artifact of tree felling. The authors conduct a review of literature to conclude the balds were a natural feature created by high intensity grazing over several million years, and most recently maintained as grazing lawns by Amerindians using fire. The authors conclude by suggesting the balds are worthy of conservation and grazing animals offers a viable management strategy.