Exotic Herbivore Species Grazing Effect On Plant Life

Module 5

SEE-U 2001 Biosphere 2 Center, AZ

Adam Nix

Eli Pristoop

J.C. Sylvan

Yuko Chitani

Mei Ying Lai

Lily Liew

Asma Madad

Prof. Tim Kittel, TA Erika Geiger

IntroductionA community is all associated

species within a given area. A variety of factors act to structure communities — factors as varied as weather fluctuations and natural disasters, to exotic species introductions, to the natural tension between producers and consumers. Whether or not the plant is killed, however, herbivory has the potential to dramatically alter plant and animal communities.

In this study the question at hand was, how grazing effects a community? What is the effect of herbivory on plant community diversity and species abundance? It is important to find out the influences that cattle grazing has on sonoran desert land. Understanding the functioning of communities is essential to conserve endangered ecosystems and the species therein. The only way to accumulate data on this is to measure the percent of plant life forms.

Site Locations

Methods

Three different sites were chosen to represent the varying intensity of herbivory on plant communities: area 1 experienced little or no grazing by cattle. Area 2, which was fenced off, experienced moderate grazing by cattle; 64 head of cattle ranged this area for a period of 3 months prior to this study. Area 3, also fenced off, was highly utilized by neighboring ranchers as rangeland. Observation indicated that this area had experienced a high intensity of cattle grazing. The line intercept sampling was used to determine the aerial cover of species (as oppsed to basal cover) on a 50-meter line within the three sites. The distance of the line to the fence of each respective site was also recorded. The line was then divided into 10-meter sections. Working in pairs, we identified each intersecting species and their coverage.

Sample bags were labeled with: site, location on the 10-meter sections from which it was collected, specie name, and lifeform. 6 GPS readings were taken at the three sites, at the beginning and end of the line. The data was then put into Excel.

We selected four other species that were representative of the changes in the percent cover over the three areas: Boraginaceae Family #1, Calliandra eriophylla, Hilaria belangeri, Opuntia engelmanni

Absolute percent cover measures the specie’s proportion in respect to the length of the line sampled (50m).

Relative percent cover measures the specie’s proportion in respect to the total length of all species sampled (>50m).

Herbacious Woody Succulent

Grass Forb Tree Shrub

Annual Perennial Annual Perennial Broad-leaf

Micro-fyllous

Borad-leaf

Micro-fyllous

Plant Lifeform Classification

Bunch grass

Sod-forming

Draught deciduous

Draught deciduous

Draught deciduous

Draught deciduous

Cold deciduous

Cold deciduous

Cold deciduous

Cold deciduous

Evergreen Evergreen Evergreen Evergreen

Sarcostemma cynanchoides sp. Hartwegii, a vine, was classified as a perennial forb.

ResultsRESULTS

1) Plant coverage: Area 1 (ungrazed) > Area 2 (moderately grazed) > Area 3 (heavily grazed). The percent coverage of annual forbs dropped from 55% relative coverage in Area 1 to 52% in Area 2 to only 14% in Area 3 (see fig. 1, 2, 3).

2) As total plant coverage diminished, relative and absolute % values achieved parity (see fig. 3).

3) Overall bare ground increased from Area 1< 2 < 3 (see fig. 4, 9).

4) Four species represent the changes in the percent cover over the three areas: Boraginaceae Family #1, Calliandra eriophylla, Hilaria belangeri, Opuntia engelmanni. While some species displayed a decrease in percent cover, others tended to increase (e.g. succulents increases from Area 1 (9.2%) to Area 2 (16.5%) and Area 3 (24.2%)) (see fig. 9).

5) Species diversity remains constant over three areas (see fig. 10).

6) Lifeform diversity also remains constant over three areas (see fig. 10).

Relative vs. Absolute Percent Coverage by Lifeforms in Area 1

0%

10%

20%

30%

40%

50%

60%

Annual Grasses Perennial BunchGrasses

Annual Forbs Perennial Forbs MicrophyllousDeciduous

Shrubs

MicrophyllousDeciduous

Trees

Succulents

Lifeform

Pe

rce

nt

Co

vera

ge

relative %

absolute %

Fig. 1

Relative vs. Absolute Percent Coverage by Lifeform in Area 2

0%

10%

20%

30%

40%

50%

60%

Annual Grass Perennial BunchGrass

Annual Forbs Perennial Forbs MicrophyllousDeciduous

Shrubs

MicrophyllousDeciduous

Trees

Succulents

Lifeform

Pe

rce

nt

Co

vera

ge

relative %

absolute %

Fig. 2

Relative vs. Absolute Percent Coverage by lifeform for Area 3

0%

2%

4%

6%

8%

10%

12%

14%

16%

Annual Grass PerennialBunch Grass

PerennialSod-forming

Grass

Annual Forbs PerennialForbs

MicrophyllousDeciduous

Shrubs

MicrophyllousDeciduous

Trees

Succulents

Lifeform

Pe

rce

nt

Co

vera

ge

Relative (%)

Absolute (%)

Fig. 3

Fig. 4

Comparison of Absolute % Cover by Lifeform in Areas 1,2,3

0%

10%

20%

30%

40%

50%

60%

Annua

l Gra

ss

Pere

nnial

Bun

ch G

rass

Pere

nnial

Sod

-form

ing G

rass

Annua

l For

bs

Pere

nnial

For

bs

Microp

hyllo

us D

ecidu

ous

Shrub

s

Microp

hyllo

us D

ecidu

ous

Tree

s

Succu

lents

Bare

Groun

d

Lifeforms

Pe

rce

nt

Co

ver

Absolute % (1)

Absolute % (2)

Absolute % (3)

Fig. 5

Comparison of Relative % Cover by Lifeform Areas 1,2,3

0%

10%

20%

30%

40%

50%

60%

Annual Grass Perennial Bunch

Grass

Perennial Sod-

forming Grass

Annual Forbs Perennial Forbs Microphy llous

Deciduous

Shrubs

Microphy llous

Deciduous

Trees

Succulents

Lifeform

Pe

rce

nt

Co

ver

Relative % (1)

Relative % (2)

Relative % (3)

Relative vs. Absolute Cover Percentages in Area 1

0.00%

5.00%

10.00%

15.00%

20.00%

25.00%

Acacia

gre

ggii

Aristid

a te

rnipe

s va

r. ge

ntilis

Bothr

iochlo

a ba

rbino

dis

Boute

loua

hirsu

ta

Callian

dra

eriop

hylla

Daucu

s pu

sillus

= S

pecie

s H

Echin

ocer

eus

Erag

rost

is cu

rvula

Erige

ron

diver

gens

= S

pecie

s A

Gilia s

p.

Lept

ochlo

a du

bia =

Spe

cies

B

Micros

eris

linea

rifoli

a =

Specie

s D

Opunt

ia ph

aeac

anth

a

Pros

opis

velut

ina =

Mes

quite

Viguier

a lon

gifoli

a =

Specie

s F

BARE GROUND

Species

Pe

rce

nt

Co

vera

ge

Relative Cover (%)

Absolute Cover (%)

Fig. 6

Relative vs. Absolute Percent Coverage in Area 2

0.00%

5.00%

10.00%

15.00%

20.00%

25.00%

Ambros

ia co

nfer

tiflor

a

Borag

inace

ae F

amily

#1

Borag

inace

ae F

amily

#3

Boute

loua

curti

penb

ula

Callian

dra

eriop

hylla

Daucu

s pu

sillus

= S

pecie

s H

Echin

ocer

eus

Erag

rost

is cu

rvula

Eriog

onum

wrig

htii

Gnaph

alium

Lept

ochlo

a du

bia =

Spe

cies

B

Micros

eris

linea

rifoli

a =

Specie

s D

Opunt

ia en

gelm

anni

Opunt

ia sp

inosio

r

Pros

opis

velut

ina =

Mes

quite

Viguier

a lon

gifoli

a =

Specie

s F

LITTE

R, INCLU

DING D

EAD C

ACTI

Species

Pe

rce

nt

Co

vera

ge Relative Cover (%)

Absolute Cover (%)

Fig. 7

Relative vs. Absolute Percent Coverage in Area 3

0.00%

10.00%

20.00%

30.00%

40.00%

50.00%

60.00%

Am

bros

ia

Aris

tida

tern

ipes

Bor

agin

acea

e

Bou

telo

ua

Bro

mus

rub

ens

Dau

cus

pusi

llus

Elym

us

Erag

rost

is

Gilia

sp.

Lepi

dium

Mac

haer

anth

era

Opu

ntia

Plan

tago

Sar

cost

emm

a

BA

RE

GR

OU

ND

LITT

ER,

Species

Pe

rce

nt

Co

ve

rag

e Relative Cover (%)

Absolute Cover (%)

Fig. 8

Comparison of Absolute Percent Coverages of 5 Selected Species for Areas 1,2,3

0.00%

10.00%

20.00%

30.00%

40.00%

50.00%

60.00%

BARE GROUND Boraginaceae Family#1

Calliandra eriophylla Hilaria belangeri Opuntia engelmanni

Species (excluding "Bare Ground")

Ab

so

lute

Pe

rce

nt

Co

vera

ge

Area 1

Area 2

Area 3

Fig. 9

Total Number of Collected Species and Total Lifeforms Present Under Different Grazing Treatments

0

5

10

15

20

25

30

35

Area 1: Ungrazed Area 2: Moderately Grazed Area 3: Heavily Grazed

Grazing Treatment

Nu

mb

er

of

Sp

eci

es

/Lif

efo

rms

Species

Lifeforms

Fig. 10

Plant Species Found at Sites• Acacia greggii• Ambrosia confertiflora• Androsace occidentalis• Aristida ternipes var. gentilis• Boraginaceae Family #1• Boraginaceae Family #2 = Species K• Boraginaceae Family #3• Bothriochloa barbinodis• Bouteloua curtipenbula• Bouteloua hirsuta

• Bromus rubens• Calliandra eriophylla • Chenopodium sp.• Daucus pusillus = Species H• Descurainia pinnata = Species E• Echinocereus• Elymus elymoides• Eragrostis curvula• Eragrostis intermedia• Erigeron divergens = Species A• Eriogonum wrightii• Gilia sp.• Gnaphalium

•Hilaria belangeri•Lepidium lasiocarpum•Leptochloa dubia = Species B•Lupinus concinnus(?)•Machaeranthera tagetina•Microseris linearifolia = Species D

•Opuntia chlorotica

•Opuntia engelmanni

•Opuntia phaeacantha

•Opuntia spinosior

•Plantago patagonica

•Prosopis velutina = Mesquite

•Sarcostemma cynanchoides ssp. Hartwegii

•Sisymbrium irio L.

•Tridens muticus = Species J2

•Triodanis perfoliata = Species J1

•Viguiera longifolia = Species F

•Species I

•BARE GROUND

•DUNG

•LITTER

DiscussionHow Does Grazing Affect

Plant Community Diversity and Species Abundance?

To answer this question, we studied three different sites: Area 1 an ungrazed range, Area 2 a moderately grazed range, and Area 3 a heavily grazed open range. From general observation, it was clear that the heavily grazed site had the least abundance of plants and a lot of bare ground between markings. It also took us considerably less time to sample the heavily grazed site than it did for the other two sites.

We measured the plant community’s overall richness of species by analyzing the number of species found and collected in each of the three areas. The possible sources of error include: misidentification of plants, inconsistency and inaccuracy in measuring technique, uncertainty in whether the lines sampled were representative of the different areas.

Conclusion

 

 

•Intense herbivory has an effect on the lifeform composition of the plant community.

•However, herbivory does not necessarily affect the biodiversity of the community.

In this exercise we learned:• Plant identification and classification• Relative and absolute percent coverages

Epple, Anne Orth. A Field Guide to the Plants of Arizona. Lew Ann Publishing Company, Mesa, Arizona. 1995.

Gould, Frank W. Grasses of the Southwestern United States. University of Arizona Press, Tucson. 1993.

Kearney, Thomas H. and Peebles, Robert H. Arizona Flora. University of California Press, Berkeley. 1960.

Niehaus, Theodore F. A Field Guide to Southwestern and Texas Wildflowers. Houghton Mifflin Co., New York. 1984.

Robbins, Travis, David Lancaster, Janna Lancaster and Dr. Tony Burgess. Biosphere 2 Centre Plant Field Guide. (Unpublished).

References

Thanks to Tim and Erika for their

expertise in plant identification.