Impact of Grazing on Prairie Soil Nutrient Levels and Biodiversity

HONORS: Writing Environmental WrongsFall Semester 2010

Jordyn Arndt

INTRODUCTION

BACKGROUND INFORMATION

Pertinent Biological Processes

Carbon Cycle Basics• Important for living things• Moves in a cycle from the

of the atmosphere, plants, and animals

• Carbon is found in living things, the atmosphere, soil, water, and rocks

© 2010 National Earth Science Teachers Association

Pertinent Biological Processes

Nitrogen Cycle Basics• Important for living things• Found naturally in soil• More nitrogen found in

areas that have animal excrement and/or decaying living things

• Nitrogen-rich chemical and natural fertilizers used to enhance plant growth

© 2010 National Earth Science Teachers Association

Role of Bison in the Prairie

Historical Perspective• Interaction of bison with the prairie• History of destruction of bison and prairie

Present Perspective• Relatively few native or restored prairie • Even fewer native or restored prairie with bison• Relatively few studies on bison and the prairie

Additional research is needed in order to better understand the interaction of bison with the North American tallgrass prairie

Questions and Hypotheses

Purpose of Research• Analyze the impact of grazing on soil nutrient levels in the

prairies of Afton, MN• Analyze the impact of grazing on prairie biodiversity

Anticipated Outcomes• Hypothesis 1: Nitrogen content < grazed prairie

Plants being consumed will need to absorb more nutrients from the soil for aboveground growth

• Hypothesis 2: Nitrogen content > grazed prairieGrazing would stimulate nitrogen cycling through process of consumption, digestion, and excretion

LITERATURE REVIEW

Mammalian Herbivores: Ecosystem-Level Effects in Two Grassland National Parks

Researcher: James K. DetlingWhere: Kansas and WyomingStudy: • Effects of mammalian herbivore grazing on plant

species composition, bio-mass, productivity, and nitrogen cycling

Results:• Biodiversity > in prairie grazed by prairie dogs• Prairie dogs > impact on plant community• Bison + prairie dogs > than each species alone

• N-concentration > in grazed prairie• N-concentration and grass > where bison

urinate• Changes in biodiversity take years• Variation in years of managed sites can be more

influential than the impact of grazing(Detling 1998)

Mammalian Herbivores: Ecosystem-Level Effects in Two Grassland National Parks

More forbs and dwarf shrubs present in the grazed prairie, however significant differences did not exist (P > 0.05)

“There were remarkably few differences in plant cover…This result was unexpected in view of numerous reports of changes in plant species diversity, equitability, species richness, and species composition after exclusion of grazers from an area” (Detling 6).

Possible factor: The amount of time in which the grazed prairie was grazed. The grazing enclosure was established in 1938, but most of this area had not been grazed since this time. Previous studies confirm that time impacts biodiversity.

(Detling 1998)

Impact of Grazing on Soil Nutrients in a Pampean

GrasslandResearchers: Raul S. Lavado, Jorge O. Sierra, and

Patricia N. HashimotoWhere: Pampean Grassland, ArgentinaStudy: • Effect of different grazing histories on the status

and spatial variability of soil organic matter and major nutrients (nitrogen and phosphorus)

Results:• Nitrogen and phosphorus > excreta returns• Grazing affects the pattern of spatial variability

of C, N, and P and spatial distribution dependant on differential effects of animal excreta

• Carbon content of soil > soil surface litter

(Lavado, Sierra, Hashimoto 1996)

Impact of Grazing on Soil Nutrients in a Pampean

Grassland (Lavado, Sierra, Hashimoto 1996)

No significant differences (p < 0.05) for organic carbon (OC) and total nitrogen (TN) between grazing conditions.

Mineral nitrogen content higher in ungrazed areas on both dates

> >

Study recognizes that, “…Literature dealing with the effects of grazing on soil organic matter and nutrient status is sometimes contradictory…It is a reflection of different environments, soils and grazing management” (Lavado, Sierra, Hashimoto 2).

Possible factor: Nitrogen content in ungrazed > grazed due to higher biological activity in grazed

The Keystone Role of Bison in North American Tallgrass Prairie

(Knapp et al. 1996)

Researchers: Alan K. Knapp et al.Where: KansasStudy: • First synthesis of the research at Konza Prairie

studying bison-tallgrass interactions since 1990Results:• Short-term different from long-term effects• Biodiversity > in prairie grazed by bison• Bison consume higher proportions of the

dominant grasses while avoiding forbs• Forbs > in prairie grazed by bison• N-concentration > in grazed prairie• Bison prefer grazing on urine-treated plots• Leaf nitrogen content > in urine-treated plots• Other effects of bison on prairie: wallowing and

death also affect biodiversity and soil nutrients

The Keystone Role of Bison in North American Tallgrass Prairie

(Knapp et al. 1996)

Study states, “…Their [bison] effects on nitrogen cycling are critical because nitrogen availability often limits plant productivity in these grasslands (Seastedt et al. 1991, Blair 1997, Turner et al. 1997) and influences plant species composition (Gibson et al. 1993, Wedin and Tilman 1993)” (Knapp et al. 44).

METHODS

Belwin ConservancyBelwin Conservancy• 1,300 acre preserve of oak savanna

and woodlands, tallgrass prairie, wetlands and fens

• Dedicated to land conservation, scientifically–based ecological restoration

• Bison introduced in 2008

Data Collection ProcessSoil Nutrient Content• Seven soil samples from grazed and

ungrazed prairie taken with an auger approximately 18 cm below ground

• Samples taken with random number table• Soil samples refrigerated for one week• Moisture content, % organic matter, and C:N

ratio assessed• Data compiled and analyzedPlant Biodiversity• Seven plots were assessed in the near

vicinity of previous soil data collection sites• Sample plots determined by throwing a

frame over a patch of prairie• Within this framed prairie patch, land cover

of bare ground, litter, specific species of grasses, and specific species of forbs were estimated

Data Collection at Belwin Conservancy

RESULTS

Analytical Tools• Carbon to Nitrogen Ratio• Percentage of Organic Matter in Soil• Percent Cover of Forbs and Grasses

Percentage of Carbon in Soil

Ungrazed Grazed1.57

1.58

1.59

1.6

1.61

1.62

1.63

1.64

1.65

1.66

1.67Pe

rcen

tage

of C

arbo

n in

Soi

l

1.6070 1.6623

Can conclude that there is no significant difference due to overlapping standard error bars

Percentage of Nitrogen in Soil

Ungrazed Grazed0.136

0.137

0.138

0.139

0.14

0.141

0.142Pe

rcen

tage

of N

itro

gen

in S

oil 0.1379 0.141

0

Can conclude that there is no significant difference due to overlapping standard error bars

Ratio of Carbon to Nitrogen in Soil

Ungrazed Grazed13.55

13.56

13.57

13.58

13.59

13.6

13.61

13.62Ra

tio o

f Car

bon

to N

itrog

en i

n So

ilt-test, p = 0.9

13.5710 13.6074

Can conclude that there is no significant difference (P > 0.05) because t-test indicates that P = 0.9

Percentage of Organic Matter in Soil

Ungrazed Grazed17.5

18

18.5

19

19.5

20

20.5Pe

rcen

tage

of O

rgan

ic M

atter

in S

oil

t-test, p = 0.4

20.166618.5627

Can conclude that there is no significant difference (P > 0.05) because t-test indicates that P = 0.4

Percent Cover of Forbs and GrassesForbs

• Goldenrod• Marigold• Desmodium• Aster• Sunflower• White Sweet Clover• Fescue• Mint• Golden Alexander• Yellow Cone• Ox-Eye• Dandelion

Grasses• Brome• Indian Grass• Big Blue Stem

Bare Ground

Litter

ungrazed grazed0

10

20

30

40

50

60

70

Average total % forbes

Average total % grass

Perc

enta

ge C

over

of F

orbs

and

Gra

sses

forbs

• There is perhaps a trend that grazed prairie has a higher percentage of forbs than ungrazed, but there is no significant difference

• Grazed prairie has a lower percentage of grasses than ungrazed, and there is significant difference P = 0.028 (P > 0.05)

Prairie Biodiversity

Prairie Biodiversity

DISCUSSION AND CONCLUSIONS

Conclusions to Study

Factors Impacting ResultsLocation of Study:• Belwin Conservancy’s role in land management• Number of years prairie has been grazed• Number of bison grazing• Amount of time annually that bison spend grazingStudy Design: • Sample size• Amount of time in which samples are gathered

Additional research is needed in order to better understand the interaction of bison with the North American tallgrass prairie

REFERENCES CITED

Works Cited• Belwin Conservancy. "Bison." Belwin Conservancy. Belwin Conservancy, 2007. Web. 7 Dec 2010. <http://www.belwin.org/bison/>.

• Belwin Conservancy. "Home." Belwin Conservancy. Belwin Conservancy, 2007. Web. 7 Dec 2010. <http://www.belwin.org/>.

• The Center for Innovation in Engineering and Science Education. "Nitrogen Cycle." Oceans Connecting a Nation. Stevens Institute of Technology, 2007. Web. 19 Oct 2010. <http://www.ciese.org/curriculum/oceansproj_new/students/cycle.html>.

• Detling, James K. (1998). Mammalian herbivores: ecosystem-level effects in two grassland national parks. Wildlife Society Bulletin, 26(3)1-12, Retrieved from http://www.jstor.org/stable/3783756

• Dorn, Tom. "Nitrogen Sources." University of Nebraska Cooperative Extension in Lancaster County. University of Nebraska Cooperative Extension, 2001. Web. 19 Oct 2010. <http://lancaster.unl.edu/ag/factsheets/288.htm>.

• Gardiner, Lisa. "The Nitrogen Cycle." Windows to the Universe. National Earth Science Teachers Association (NESTA), 07 May 2007. Web. 06 Dec 2010. <http://windows2universe.org/earth/Life/nitrogen_cycle>.

• Johnson, Roberta. "The Carbon Cycle." Windows to the Universe. National Earth Science Teachers Association (NESTA), 07 Nov 2010. Web. 06 Dec 2010. <http://windows2universe.org/earth/Water/co2_cycle.html>.

• Knapp, Alan K., Blair, John M., Collins, Scott L., Hartnett, David C., Johnson, Loretta C., & Towne, E Gene. (1999). The keystone role of bison in north american tallgrass prairie. BioScience, 49(1), 1-13, Retrieved from http://www.jstor.org/stable/1313492

• Lavado, Raul S., Sierra, Jorge O., & Hashimoto, Patricia N. (1996). Impact of grazing on soil nutrients in a pampean grassland. Journal of Range Management,49 (5) 1-7, Retrieved from http://www.jstor.org/stable/4002929

• Tucker, M. Ray. "Essential Plant Nutrients: their presence in North Carolina soils and role in plant nutrition."North Carolina Department of Agriculture & Consumer Services. NCDA & CS Agronomic Division, Oct 1999. Web. 23 Nov 2010. <http://www.ncagr.gov/agronomi/pdffiles/essnutr.pdf>