Influence of Chinese privet (Ligustrum sinense Lour.) on floodplain productivity and regeneration

Eve Brantley, Jennifer Mitchell, and B. Graeme LockabyAuburn University School of Forestry and Wildlife SciencesCenter for Forest Sustainability

Ligustrum sinense Lour.• Often forms dense thickets, particularly in bottomland

forests and along fencerows

• Shade and flood tolerant

• Aggressive colonizer - spreads locally by root sprouts and widely by abundant bird- and other animal-dispersed seeds.

Invasive Plants of the Eastern United States

• Present in all of the southeastern states and ranges north to Massachusetts

Objectives• To determine how increasing densities of Chinese privet

influence aboveground and belowground net primary productivity.

• Investigate influence of Chinese privet density on native plant regeneration

Study Sites• 16 - 0.04 ha study sites selected in West Georgia

• Southern Piedmont

• Floodplains occupied by deciduous forests, closed canopy

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Georgia, USA

Columbus GA

LaGrange GA

Study Sites

• Sites represent a continuum of understory Chinese privet stem density (0 – 100%)

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

BLN

1

BLN

2

BLN

3

MU

3

RB1

SC2

SC1

MU

2

RB3

SB2-

1

SB2-

2

MU

1

RB2

SB4-

3

SB4-

1

SB4-

2

Prop

ortio

n of

ste

ms

as C

hine

se p

rivet

Study sites

To determine how increasing densities of Chinese privet influence above- and belowground net primary productivity.

Aboveground productivity:• Monthly collection of litterfall (3 -.25 m2 traps per site)

• Litterfall samples dried, weighed and analyzed for C, N, P

• Diameter at breast height (DBH) recorded annually for all stems greater than 10 cm DBH and used to estimate stem annual increment

To determine how increasing densities of Chinese privet influence above- and belowground net primary productivity.

Belowground productivity:• Two fine root samples collected every 6-8 weeks using

soil core method (Vogt and Persson 1991, Anderson and Ingram 1993, Bledsoe et al. 1999)

• Samples collected to a depth of 11 cm and sorted size classes by live and dead fractions

• Samples dried, weighed

and analyzed for C and N

Investigate influence of Chinese privet density on native plant regeneration

Regeneration:• 12 – 1 m2 plots established at 3, 6 and 9M from site

center on north, south, east, and west ordination

• After spring leaf out, vegetation in each regen plot less than 10 cm DBH will be identified to species and its height recorded

Statistics• SAS version 9.1

• Linear and non-linear regression

• All differences below p < 0.10 reported

Year 1 Results

Increasing privet understory

Net Primary Productivity, Year 1

0

500

1000

1500

2000

2500

3000

3500

BLN

1

BLN

2

BLN

3

MU

13

RB

1

SC

2

SC

1

MU

12

RB

3

SB

21

SB

22

MU

11

RB

2

SB

43

SB

41

SB

42

g/m

2/yr

Roots Stem NPP Litterfall

Year 1 Results

• Chinese privet presence measured by proportion of understory - percent of understory that is Chinese privet (0 – 100%)

• Curvilinear and linear relationships between Net Primary Productivity and privet invasion

• Strong, negative relationship between Chinese privet invasion and native plant regneration

Net Primary Productivity and Chinese privet understory proportion

Significant curvilinear relationship between

– Total NPP & proportion of understory as privet

(P < 0.008 R2 .5821)

0

500

1000

1500

2000

2500

3000

3500

0 20 40 60 80 100

% understory privet 2004

tota

l npp

g/m

2/yr

Net Primary Productivity and Chinese privet understory proportion

Significant curvilinear relationship between

– Aboveground NPP & proportion of understory as privet

(P < 0.05 R2 .4133)

0

500

1000

1500

2000

2500

0 20 40 60 80 100

% understory privet 2004

tota

l ab

ove

gro

un

d n

pp

g/m

2/yr

Net Primary Productivity and Chinese privet understory proportion

Significant nonlinear relationship between

– Belowground NPP & proportion of understory as privet

(P < 0.01 R2 .5311)

0

200

400

600

800

1000

1200

0 20 40 60 80 100

% understory privet 2004

bel

ow

gro

un

d n

pp

g/m

2/yr

Regeneration

% Chinese Privet Understory (2004) compared with % Chinese Privet in Regeneration Layer (2005)

y = 0.9688x + 5.9086 (p < 0.001 R2 = 0.933)

0

20

40

60

80

100

0 20 40 60 80 100

% Understory Chinese Privet 2004

% R

eg

en

era

tion

Ch

ine

se P

rive

t 2

00

5

Regeneration

% Chinese Privet Understory (2004) compared with % Native Species in Regeneration Layer (2005)

y = -0.9641x + 94.115 (p < 0.001 R2 = 0.9472)

0

20

40

60

80

100

0 20 40 60 80 100

% Understory Chinese Privet 2004

% R

egen

erat

ion

Nat

ive

Spe

cies

20

05

Year 1 Conclusions - NPP

• In southeastern Piedmont riparian areas Chinese privet appears to influence

– Net Primary Productivity

– Native species regeneration

As Chinese privet stem densities rise:

• ANPP is the greatest at medium levels of Chinese privet understory proportion (40-80%)

• ANPP is lower at the low (0-40%) and high (80-100%) levels of Chinese privet understory proportion

As Chinese privet stem densities rise:

• BNPP is the greatest at medium levels of Chinese privet understory proportion (40-80%)

• BNPP is lower at the low (0-40%) and high (80-100%) levels of Chinese privet understory proportion

Year 1 Conclusions – Regeneration

• Proportion of Chinese privet in the understory is strongly related to the regeneration layer

– Increase in Chinese privet regeneration with increasing proportion of understory Chinese privet

– Decrease in native species regneration with increasing proportion of understory Chinese privet

~ 50% understory privet, native regen drops below 40%

Acknowledgements

• Dr. B. Graeme Lockaby• Dr. Kathryn Flynn• Dr. William Conner• Dr. James E. Hairston

• Jennifer Mitchell• Don Vestal• Robin Governo• Lena Polyakova• Rachel Jolley• Jackie Crim• Emile Elias

Auburn University School of Forestry and Wildlife Sciences, Center for Forest Sustainability