Case Studies of Invasive Plant Impacts(unintentional, “assisted invasion”)

Bison and the “Iron Bison”

LOCAL FLORA – Lecture 12Dr. Donald P. Althoff

LEC 12

Introduced Bison Aiding Dispersal of Exotic Plants

• ___________ is a major process that can that can influence any extension of the distribution of a plant (native or non-native) a) ensure the “next” plant can land

“some” distance from the parentplant

b) that next place where it lands mightbe favorable with respect to

growing conditionsc) multiple seeds with multiple

introductions or re-introductions

Case Study: Introduced Bison on Santa Catalina Island, CA

Constible, J.M., R. A. Sweitzer, D.H. Van Vuren,P.T. Schuyler, and D.A. Kemp. 2005. Dispersalof non-native plants by introduced bison in an island ecosystem. Biological Invasions7:699-709

Santa Catalina Island is about 25 miles (40 km) west of Los Angeles, California

Island is ___ mi2 (=194 km2 = ________ acres)

Has Mediterranean climate, having moderate temperatures throughout the year, most rainfall is November - April

3 major upland habitat types:

• Coastal sage scrub• Grassland (dominated by non-native annual grasses and forbs• Island chaparral (dominated by evergreen and drought-resistent shrub and “short” trees

History of the Island• Many of the plants (annual grasses and forbs) on the

island are of __________________ origin• Santa Catalina Island Conservancy (SCIC) owns

approximately _____ of the island—mostly the interior portions. SCIC mission is to conserve native biotic and abiotic resources and restore ecosystem functioning including ___________ of invasive species believed to have significant negative impacts

• Between 1924-1935, 25 bison introduced to island. Prior to this, no large grazing animals on the island. Approximately _____ of island “available to bison to graze/roam.

More on the bison herd….• Herd is culled every 1-2 years since 1993 to maintain

it at 185-250 animals • Removal (i.e., eradication) of the herd has been

“delayed” and/or not attempted because of a) _________ importance to island

residentsb) _________ importance to island

residents• As of 2003, SCIC plan has been to maintain herd at

150 animals by periodic removals and contraceptive program

Bison have significantpotential to disperse non-native plants:

1)

2)

The spreading by hair clumpsis aided by ________ (dustingsites), which can both retain moisture because of the depression made in the ground over time, “release”of soil that can becomepart of matted hair stillclinging to the bison, and provide __________ sites (i.e., exposed sites) for seedgermination and minimal competition

Bison can disperse seeds two ways:

• _____________ – ingestion and later excretion of seeds (i.e., fecal pats). Process fairly well documented….more so cattle, which pass large numbers of viable seeds contributing to recruitment of native and non-native plant populations

• _____________ – attachment of seeds to the body of the animal. Thought to be less common mechanism of seed dispersal

Epizoochory considerations….

• Bison have thick, curly hair…ideally suited for adhesion of barbed, hooked, or viscous fruits. On the island, with Mediterranean climate, almost constant shedding. Therefore, great potential for year-round dispersal

• Bison constant use of wallows leading to deposition and germination of non-native seeds

Methods included…• Collected 1) clumps of hair shaved from bison

(from forelocks…an area that tends to be permanent and accumulate seeds over time when animals are foraging, loafing, and wallowing)-- during yearly roundup and 2) clumps dislodged by wallowing at active wallowing sites

• Samples “processed” further to determine species (if possible), abundance, and germination rates (i.e., seed viability)

Methods…con’t

• Germination trials took place in wire cage protected soils (using Santa Catalina Island soils). Cages prevented access by vertebrates as these were “outside” trials

• Also, collected some fresh fecal pats (i.e., dung). Air-dried them, then spread them over bermiculite, and then watered as the same schedule as for the hair clump seed samples to evaluate germination rates

Results (2000-2002)

• 2,552 seeds extracted from bison hair clumps obtained by shaving

• 1,612 seeds extracted from bison hair clumps collected at wallows

• Despite similarity in number of plant species (native vs non-native)….

…there were _________________ non-native seeds in hair clumps than native seeds!!!!

Bison wallows found in all major habitat types.Wallows distributed throughout most the range of bison on the island (see “dots” above)…but most were __________________________________________________________________________________________

Results…con’t• Two of the most common non-native forbs

(common horehound = CH & rough cocklebur = RC) found in hair clumps are thought to only get to novel (i.e., new) habitats by ____________. The viability of these two forb species seeds was ____ (CH) & ____ (RC) in shaved hair clumps and _____ (both CH & RC) from wallow hair clump samples

• Majority of plants that germinated from wallows hair clump trails were _________

Conclusions• Bison weren’t the only “agent” of dispersal (i.e.,

humans, native field mice, introducd rats, and introduced mule deer), but the combined effects of

a) long distance movements by bison &b) disturbance by bison (i.e., wallowing)

resulted in a “significant ___________________ _________________ seed dispersal of non-native plant on SCI”

• Most of the non-native plants seeds “tranported” are annuals hitting ______________

Conclusions..con’t• Bison hair clumps appear to transfer (transport)

more of these seeds that have high rates of germination than fecal pats

• Nonetheless, fecal pats have the ability to retain some seeds that will germinate making the __________________ dispersal mechanisms nearly as important as the hair clumps because the fecal pats are so widely distributed on the island— _______________ than the wallows. This includes __________________________________ other areas not conducive to wallowing

Management Considerations• ________ herd size (or eliminate) on the island• ________ the size of the range for the bison on

the island (still allows for tourism viewing)

• Relevance to land managers elsewhere: transporting stock from natural or semi-natural foraging grounds (i.e., winter or summer rangelands) can clearly facilitate dispersal of non-native plant seeds. Moving herds in this way can reduce the effectiveness of chemical and mechanical treatments…because of ___________ __________________!!!

THE IRON BISON IMPACT:

Fragmentation: At-risk landscapes due to invasive plants species

“micro” Fragmentation

• Power-line right-of-ways• Phone cables• Gas pipelines• Rural water lines• Wind turbine installation and service

road network

Invasibility of Plant Communities: TWO MAJOR “OPPOSING” THEORIES

• Elton (1958)

• May (1973) and Huston & DeAngelis (1994)

Elton (1958)

Exotic species might more easily invade areas of ______ species diversity because areas of high species diversity should use limiting resources more completely…thereby preventing invasion by exotic species

1

May (1973) Huston & DeAngelis (1994)

Highly DIVERSE plant communitiesare intrinsically _________ with some species dropping in and out routinely

2

Stohlgren et al. 1998

At small scales (micro-level), invasive species CAN get established at low cover, bare ground sites---

ex. _________________

Invasive species CAN get established at highly diverse sites because not all resources are used up—

ex. _________________

1

2

LCTA at Fort Riley(now RTLA)

• Program started in 1989• Permanent plots established for monitoring

trends in vegetation, small mammal, and bird communities

• Summarized dataset for 1994-2001 (8 years)

Sericea Lespedeza

• Chinese lespedeza = Chinese bush-clover• Introduced in U.S. in 1896 for erosion control, hay

production, and wildlife cover• Introduced in SE Kansas during 1930s as cover for

strip-mined lands; around state and federal reservoirs from 1940s-1970s AND in 1950s as part of soil bank program.

• 1 July 2000 declared “state wide noxious weed “ in Kansas.

Sericea Lespedeza…con’t

• Drought tolerant• ________________________________• Few natural predators/herbivores• Prolific seed producers—_______ seeds per stem not

rare. Result: 1-2 million seeds per acre can be produced

• Seeds may be viable up to ______ in the soil

Introduced

Chinese (Sericea) Lespedeza

1994 1995 1996 1997 1998 1999 2000 2001

Pro

porti

on o

f plo

ts (+

SE

)

0.0

0.2

0.4

0.6

0.8

1.0

IOC = 0.42

100,000 acresMPRC

IMPACTZONE

95

95

95

95

96

9696

96

96

97

98

98

99

9999

99

99

00

00

00

00

0000

00

0101

1995 – 4 - 31996 – 5 - 21997 – 1 - 01998 – 2 - 21999 – 5 - 22000 – 7 - 32001 – 2 - 2

Year-New Plots-Areas

Sericea lespedeza

Chinese (Sericea) Lespedeza

1994 1995 1996 1997 1998 1999 2000 2001

Pro

porti

on o

f plo

ts (+

SE

)

0.0

0.2

0.4

0.6

0.8

1.0

IOC = 0.42

Chinese Lespedeza (Sericea) FORB IntroducedCumulative No. of Plots Detected

based on "presence" data

1994 1995 1996 1997 1998 1999 2000 2001

Cum

ulat

ive

No.

of P

lots

0

5

10

15

20

25

30

Chinese (Sericea) lespedeza FORB introducedCumulative no. of new training areas detected

(based on presence data)

1994 1995 1996 1997 1998 1999 2000 2001

Cum

ulat

ive

No.

of

Trai

ning

Are

as D

etec

ted

0

5

10

15

20

Johnson Grass FORB IntroducedCumulative no. of new regions detected

(based on presence data)

1994 1995 1996 1997 1998 1999 2000 2001

Cum

ulat

ive

no. o

f new

regi

ons

0

5

10

15

20

Johnson Grass FORB IntroducedCumulative no. of new plots detected

(based on presence data)

1994 1995 1996 1997 1998 1999 2000 2001

Cum

ulat

ive

no. o

f new

plo

ts

0

5

10

15

20

25

30

95

95

96

96

96

96

97

98

98

98

98

98

98

9899

99

99

99

990000

1995 – 2 - 21996 – 4 - 21997 – 1 - 01998 – 7 - 51999 – 5 - 02000 – 2 - 02001 – 0 - 0

Year-New Plots-Areas

Johnson grass

Key Points: Fragmentation• It can be at a very ________ scale • Invasive plants (exotics) can easily acquire ______ or

________ to disperse to favorable, recently “_______” ________________ landscapes

• High diversity of surrounding “native” plant communities (riparian zones) can be _________ AND ____________ for exotics in grassland ecosystems

• ________________ sites in upland areas are very vulnerable to invasions by exotics

• On Fort Riley, wheeled and tracked vehicles probably spread seeds—especially when training exercises took place ___________________—with clumps of soil transported from area to area

For the prairie ecosystem….

• Climax vegetation type is ______________ vegetation (predominately grass and forbs)

• _______________, in “large patches” (assume something > 1-2 m2) not a “good” thing. The more slope, the more rainfall, the more “traffic” the greater the likelihood of invading species becoming established and greater degree of soil erosion