Impacts of Bohemian Knotweed

on Litter Decomposition, etc.

Shannon Claeson

Olympia PNW Research Station

USDA Forest Service

14 November 2013

• Forms dense monocultures, up to 5m tall,

• Displaces native vegetation,

• Perennial - drops leaves all at once in autumn,

• Reabsorbs nutrients from leaves prior to leaf-fall!

Bohemian Knotweed

Bohemian knotweed (Polygonum x bohemicum)

red alder (Alnus rubra)

black cottonwood (Populus trichocarpa)

Objectives

Aquatic litter processing

Aquatic litter processing

Leaves high in nutrients • more fungal biomass, • more insect shredders, • decompose faster.

Nutrients

(nitrogen,

phosphorus)

Fungi

Invertebrate

detritivores

Leaf decomposition

+

+

+

+ Leaves high in structure • less fungal biomass, • less insect shredders, • decompose slower.

Physical

abrasion

Structure

(fiber, cellulose,

lignin)

-

-

-

-

-

-

Field Experiment - Methods

Single species leaf-packs: • Leaf-pack = 5.0g of senesced, dry leaves • 3 species = alder, cottonwood, or knotweed • 3 streams = Stony, Wildcat, Porter

(Chehalis Basin) • Leaf-packs in water January-March 2011

Field Experiment - Methods

At start (day 0) and after 15, 31, & 56 days Removed 5 leaf-packs/species/stream & measured: • % Fiber, Cellulose, Lignin (day 0 only) • % Carbon, Nitrogen, Phosphorus (each time) • Dry mass (each time) • Fungal biomass (each time) • # Aquatic invertebrates (day 31 only)

Aquatic litter processing

Structure (%FCL)

Nutrients (%CNP) Fungal biomass Change in leaf mass

Insect abundance

Study Streams

StonyPorter

Wildcat

123°0'0"W124°0'0"W

47

°30

'0"N

47

°0'0

"N4

6°3

0'0

"N

Chehalis

Rive

r

WASHINGTON

0 10 20 30 Kilometers

Study reaches

Rivers

Sea water

Forested, 2nd-3rd order, pool-riffle, gravel-cobble, alder & cottonwood, support salmon.

Wildcat Creek

Stony Creek

Porter River

1

2

3

4

5

6

7

8

9

10

deg

rees

Cel

ciu

s

Water Temperature (˚C) - Daily Mean

WildcatStonyPorter

Stream Reaches (50m long)

Wildcat Creek Stony Creek Porter River

Stream Reaches

Wildcat Creek

Stony Creek

Porter River

Parameter Stony Wildcat Porter

pH 7.0 6.9 7.3

Conductivity (µS/cm) 43.5 62.7 45.9

Dissolved Oxygen (mg/L) 12.4 12.1 12.8

NO3/NO2-N (µg/L) 579 627 638

NH4-N (µg/L) 33 11 11

PO4-P (µg/L) 11 15 10

Streams similar!

Senesced Leaf Structure (day 0)

Alder

Cottonwood

Knotweed

Leaf conte

nt

(%)

0

10

20

30

40

50

60

70

80

90

100

a

Species

a a

ab b

b

b c

c

Al

Lignin Cellulose Fiber

Ct Kw Al Ct Kw Al Ct Kw

Bars are mean ± 1 SE

Tukey-Kramer adjusted p<0.05

Senesced Leaf Chemistry

a a

Alder

Cottonwood

Knotweed

Ca

rbo

n:N

itro

ge

n

10

20

30

40

50

60

70

80

90

Ca

rbo

n:P

ho

sp

ho

rus

400

500

600

700

800

900

1000

1100

1200

1300

1400

0 20 30 60 10 40 50 0 20 30 60 10 40 50

a

b

c

a

b

c

a

b b

a

b b

a

b

b

a

a

b

a

a

a

a

Time (days) Time (days)

More nitrogen/phosphorus lowers C:N/C:P ratios.

Points are mean ± 1 SE

Tukey-Kramer adjusted p<0.05

Fungal Biomass (ergosterol)

Fun

gal bio

ma

ss (

mg/g

)

0

10

20

30

40

50

60

70

80

90

Time (days)

0 20 30 60 10 40 50

a b

c

a

b

c

a

a

a

a

ab

b Alder

Cottonwood

Knotweed

Points are mean ± 1 SE

Tukey-Kramer adjusted p<0.05

Aquatic Invertebrates (day 31)

*

Bars are mean ± 1 SE

Tukey-Kramer adjusted p<0.05 *

0

50

100

150

200

250

300Abundance

0

5

10

15

20

25

Taxa Richness

0%

1%

2%

3%

4%

5%

6%

7%

8%

9%

10%Scraper

0%

5%

10%

15%

20%

25%

30%Shredder

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%Collector

0%

1%

2%

3%

4%

5%

6%

7%

8%

9%

10%Predator

Alder

Cottonwood

Knotweed

*

Functional feeding groups:

Invertebrate Community Composition (day 31)

Abundance

%CF

%CG

%SC

%SH Richness

Wildcat

Creek Porter Creek

Stony

Creek

Axis

2 (

r2 =

0.1

9)

Axis 1 (r2 = 0.63)

NMS ordination of 45 leaf-packs with 43 taxa.

Streams differed in abundance, richness, and % FFG’s.

Alder

Cottonwood

Knotweed

Mass remaining %

Mass r

em

ain

ing (

%)

0

20

40

60

80

100

Time (days)

0 20 30 60 10 40 50

a

b

b

a

a

ab

b

a

Alder

Cottonwood

Knotweed

Bars are mean ± 1 SE

Tukey-Kramer adjusted p<0.05

Results Alder leaves:

• More nutrients, less structure

Initially less fungal biomass, developed more over time

• More insect shredders

• Initially decomposed faster

Knotweed leaves:

Less nutrients, more structure

Initially more fungal biomass, developed less over time

Fewer insect shredders

Initially decomposed slower

Cottonwood leaves: in between…

Nutrients

(nitrogen,

phosphorus)

Fungi

Invertebrate

detritivores

Leaf decomposition

+

+

+

+

Physical

abrasion

Structure

(fiber, cellulose,

lignin)

-

-

-

-

-

-

Native vs. Non-native

leaf litter inputs:

Quality

? Quantity

? Timing

Wildcat Creek, Chehalis Basin, WA

Funding & Resources provided by:

• U.S. Fish & Wildlife Service

• U.S. Forest Service

• Dr. Carri LeRoy at The Evergreen State College (TESC)

• Dr. Kevin Kuehn at University of Southern Mississippi (USM)

Special thanks to:

• Jacob Barry (USM)

• Tamara Cowles, Ben Leonard, Steve Scott, Caitlin Reece (TESC)

• Environmental Analysis class 2011 (TESC)

Acknowledgements