species under experimental drought Emma Byerly & S. Luke Flory - - PowerPoint PPT Presentation

Facilitation among invasive plant species under experimental drought

Emma Byerly & S. Luke Flory

Multiple Species Invasions

• Most research focused on effects of

a single invasive species

• Usually 3 or 4 invasive plants co-

invade

• Shortage of studies on multiple

plant invaders

Kuebbing et al., 2013)

Facilitation

• Novel interactions
• Can be beneficial, neutral, or negative
• Microstegium facilitated Alliara due to offset phenologies (Flory and Bauer,

2013)

• May mitigate effects of harsh environmental conditions (Lortie et al., 2004)
• In Southeast US, seasonal droughts will occur more frequently (Mulholland and

Best 1997)

• Invasional meltdown (Simberloff & Von Holle, 1999)
• Primary invasion facilitates secondary ones

Research questions

• How do cogongrass invasions influence the establishment success of

secondary invaders?

• How do drought conditions influence these interactions?

Primary Invader

• Cogongrass (Imperata cylindrica)
• C4 rhizomatous grass
• Extensive network of rhizomes

(Dozier et al., 1998; Estrada and Flory, 2015)

• May mediate effects of drought

Secondary Invaders

• Chinese tallow tree

(Triadica sebifera)

• Prefers more mesic

conditions

• Taproot (Scheld et al.,

1981)

• Brazilian pepper tree (Schinus terebinthifolius)
• Fast growth, drought resistant, high seedling survival (Ewel et al.,

1982)

• Found in association with cogongrass (Platt et al., 2001)
• Lantana (Lantana

camara)

• Tolerates low annual

rainfall (Gujral and

Vasudevan 1983)

• Anecdotal accounts of

lantana suppressing cogongrass (Burkill 1935)

Possible Outcomes

Drought + Invasion = ↓↓ Drought + Invasion = ↑↓

+ +

Methods

• Secondary invaders planted in

plots June 2016

• Survival and performance data

collected July – November 2016

Native spp. Ambient rainfall Native spp. Drought treatment Invasion Ambient rainfall Invasion Drought treatment

X 10 replicates

Chinese Tallowtree

78% p = 0.0002 74% p = 0.0001 9x p = 0.04

2x

Lantana

4x p = 0.0191 2x p < 0.0001 1.8x 19% p = 0.004

Brazilian Peppertree

2x (p = 0.0805) 2x (p = 0.0001)

2x

Summary table

Spp. Survival Herbivory Average Biomass Total Biomass Reproduction Chinese tallow ↓78% (invasion) ↑74% (invasion) ↑868% (invasion) ↑111% (invasion) NA Lantana ↓19% (invasion) ↑213% (invasion) ↑400% (drought) NA ↑ 30% (invasion) ↑ 67% (drought) Brazilian pepper Ø ↑215% (invasion) ↑111% (invasion) ↑100% (invasion) NA

VWC water content 2015

• Soil moisture higher in

ambient plots

• Under drought

conditions, invaded plots have greater soil moisture

PAR light data 2015

Take home

• There is some evidence that cogongrass facilitates secondary invaders
• Facilitation due to drought or invasion is species-specific
• Dependent on traits of both primary and secondary invaders
• Indirect effects of invasion may mediate interactions among invaders

Acknowledgements: Chris Wilson Jules NeSmith Chrissy Alba

Flowering

• 33 individuals:
• 19 drought, resident

vegetation

• 9 ambient rainfall, invaded
• 7 drought, invaded
• Number of inflorescences,

reproductive biomass

Rodent damage