Are we creating the idealconditions for Arundo donax

invasion in California?

Gretchen CoffmanRichard F. Ambrose

Tom DudleyPhil W. Rundel

UCLA

Arundo (Arundo donax)• Indigenous to northern

India and southern Nepal, a Wet-Dry Tropical Climate

• Bamboo-like member of Grass family

• 8-10 meters tall• Spreads via massive

rhizomes

PROBLEM

• Introduced globally for use in erosion control, ceilings, roofs, fences, baskets, and around hot springs

• Successful invader in river systems of Southern CA in past 35 years

Distribution

Why is Arundo So Successful?• Easily dispersed via rhizomes• Disturbance colonizer • Successful in Mediterranean-type

climate– fast growing (up to 7 cm per day)– reaches >8 m in height after only

a few months– grows 3-4 times faster than native

plants• Outcompetes indigenous plant

species for resources Bell 1994

Factors Thought to Contribute to Invasion

• Water• Nutrients • Light• Fire

IMPORT AND EXPORT OF WATER

NUTRIENT INPUTS

LOTS OF LIGHT...

October 2003

FIRE !!!

Invasion Hypothesis

Increased water, nutrients, light, and fire in riparian ecosystems have made a significant contribution to the successful invasion of Arundo (Arundo donax) throughout river systems in Mediterranean-type climates like California

Study Approaches

• Experimental study -• large-scale field experiment (2002-5)

• Correlational field study -• opportunistic fire study (2003-4)

Study Area Santa Clara River Watershed

Field Experiment

Stillwater Sciences

Field Experiment

HRNA

Santa Clara River

South Mountain RoadN

Riparian Field Experiment

• Large-scale field experiment (0.4 ha)– 1,152 plants – 8 competition treatments (4 species)– 3 nutrient treatments– 2 water treatments– 2 light treatments

Study Design1 2 3 4 5 6 7 8 9

M A C C M A W A M M W A A A M A C C C C C A M M A A A A W W C A W A C A A C M M W C A M W W W WL H L L H L H H L H H L H L H L

A M C C A M A W M M A W A A A M C C C C A C M M A A A A W W A C A W A C M W M M M A C W W W W W

M M W A M M C A W A A A M A M A A A W W W A C C C C C A M M A A M A C C M A W M W W W W A M C AL H H L L H L H H L H H L H L L

M M A W M M A C A W A A A M C W A A W W A W C C C C A C M M A A A M C C A M A C W W W W W C A C

C C M A C A W C W A M A M M C W W W C C W A C C M C M M A A A A M M C A W W M A C A W W A A W AH L L H L H L H H H L L L H H L

C C A M A C A M A W A M M M A M W W C C A W C C W A M M A A A A M M A C W W A M A C W W A A A W

C A C A A A W W M M M M W A W W A A M A W A A A C C W A C C C A M A M A M W C A C C W W A W M ML L L L L H H L H H H L H H L H

A C A C A A W W M M M M A W W W A A A M A W A A C C A W C C A C A M A M A C W M C C W W C M M M

W A A A C A C C C A M M C C C A W A W W A A C C M A W W M A A A C A M M W A M M A W M A M C W WH H L L H H L L H L L H L H L

A W A A A C C C A C M M C C M W A W W W A A C C A M W W A M A A A C M M A W M M M C A M W A W W

W A C C W A W A C W M M M M A A C A M A A A W A W C A A C A C C W W W W W W C C M A C A M M M AH H H L L L H L L H H L H L H L

A W C C M C A W M A M M M M A A A C A M A A A W A M A A A C C C W W W W W W C C A M A C M M A M

LEGEND:

A = Arundo donax (Giant Reed) = Open treatmentC = Black Cottonwood (Populus balsamifera ssp. trichocarpa ) = Shade treatment (80%)M = Mule Fat (Baccharis salicifolia ) = Plant grouping numberW = Red Willow (Salix laevigata ) C AH = High N fertilizer treatment H = Plant groupingL = Low N fertilizer treatment A C

249 250 251245 246 247 248241 242 243 244

200 201 202 203

153 154 155

193 194 195 196 197 198 199

149 150 151 152145 146 147 148

104 105 106 107

57 58 59

97 98 99 100 101 102 103

53 54 55 5649 50 51 52

261 262 263 264257 258 259 260253 254 255 256

213 214 215 216209 210 211 212205 206 207 208

165 166 167 168161 162 163 164157 158 159 160

117 118 119 120113 114 115 116109 110 111 112

69 70 71 7265 66 67 6861 62 63 64

21 22 23 2417 18 19 2013 14 15 16

11

10 11 12

60

108

156

204

252

Groundwater wellsand soil moisture sensors

Measurements• Biomass• Growth• Soil moisture• Groundwater levels• Soil grain size• Leaf area• Leaf nutrient

content• Water potential

Results

Plant Species

Dry

Abo

vegr

ound

Bio

mas

s (g

)

0

200

400

600

800

1000

1200

1400

1600

High Soil Moisture Low Soil Moisture

Arundo donaxBlack

CottonwoodMulefat

Red Willow

Water AvailabilitySoil Moisture

Light Availability

Plant Species

Dry

Abo

vegr

ound

Bio

mas

s (g

)

0

200

400

600

800

1000

1200

1400

1600

1800

Arundo donaxBlack

CottonwoodMulefat

Red Willow

Plant Species

0

200

400

600

800

1000

SHADEOPEN

Arundo donaxBlack

Cottonwood MulefatRed Willow

Low Soil MoistureHigh Soil Moisture

Summer 2003

Nutrient Availability

Plant Species

Dry

Abo

vegr

ound

Bio

mas

s (g

)

0

200

400

600

800

1000

1200

1400

1600

1800

2000

Arundo donaxBlack

Cottonwood MulefatRed Willow

Plant Species

0

200

400

600

800

1000

NO FERTILIZER LOW FERTILIZER HIGH FERTILIZER

Arundo donaxBlack

Cottonwood MulefatRed Willow

High Soil Moisture Low Soil Moisture

Summer 2003

1

23 46 5

7-1415

Fire Studies• Documented

historical spread of fire through Arundoin 9 rivers in Southern CA

• Measured growth, density and % cover of Arundo vs. natives after fire

Extent of fire

Rapid Arundo growth after fire

6 months8 weeks

Post-Fire Growth

Time after FireNovember

DecemberJanuary

February March April May June JulyAugust

September

Ave

rage

Ran

dom

Hei

ght (

cm)

-50

0

50

100

150

200

250

300

350

Arundo donaxNative Plant SpeciesTrends over time

Time Post-fire (2004)

March April June July August SeptemberM

ean

Den

sity

(ste

m/m

2 )

0

5

10

15

20

25

30

Arundo donaxNative Plant SpeciesTrends over time

Plant Abundance

0

20

40

60

80

Arundo donaxNative Plants

Summer 2003Pre-fire

July 2004Post-fire

Time

Plan

t Abu

ndan

ce (p

erce

nt c

over

/m2 )

SummaryWater Import/Export

Nutrient Inputs

Removal of MatureRiparian Forest

Fire

Acknowledgements• Funding:

– UC Water Resources Center– State Coastal Conservancy– Santa Clara River Trustee Council– The Nature Conservancy– University Research Expedition Program– Rico International– UCLA/UCSB

• Thanks to my many field assistants and volunteers in the Western Cape, South Africa and Southern California who made this research possible!