Linking physiological traits and species abundance to invasion resistance

Jeremy James Framework

• Plant community composition influences ecosystem properties

• Much emphasis on effects of functional group diversity on ecosystem properties

• Invasive plant management can be improved by managing plant communities based on functional traits as opposed to functional groups Outline • An example of how functional traits influence ecosystem properties (N capture and invasion) – Traits related to N capture – Trait effects on ecosystems are moderated by species abundance

• What traits might be important to consider when revegetating areas prone to weed invasion? – At the seedling stage traits affecting initial growth rate important

• Conclusions and future directions Functional group diversity, nitrogen capture and invasion resistance Study site

Group Code Common Name Scientific Name Annual BRTE cheatgrass Bromus tectorum L. Annual TACA medusahead Taeniatherum caput-medusae (L.) Nevski Bunchgrass PSSP bluebunch wheatgrass Pseudoroegneria spicata (Pursh) A. Löve Bunchgrass ELEL bottlebrush squirreltail Elymus elymoides (Raf.) Swezey Bunchgrass POSE Sandberg’s bluegrass Poa secunda J. Presl Forb LOTR nineleaf biscuitroot Lomatium triternatum (Pursh) Coult. & Rose Forb CRIN grey hawksbeard Crepis intermedia Gray

Experimental design

• 15N was injected into soils around 7 study species • Injections were made: – 3 times during the growing season (April, May June) – At 2 soil depth (2-7 cm, 17-22 cm) + - – Using 2 forms of N (NH4 , NO3 ) • Removal plots – Medusahead establishment in plots where different functional groups removed N partitioning through time

April May 60

40

20 N capture (% of each species total) 15 Annuals Bunchgrasses Sandberg Forbs N partitioning by soil depth

100 2-7 cm 17-22 cm 80

60

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20 N capture (% of each species total) each species N capture (% of 15 Annuals Bunchgrasses Sandberg Forbs Integrating N uptake patterns and species abundance Influence on ecosystem = trait × abundance

Portion of community biomass

annuals Nitrogen uptake × bunchgrasses Sandberg forbs Total Ncapture

15N capture (mg m-2) 0.5 1.0 1.5 2.0 0.0 0.5 1.0 1.5 2.0 1.0 2.0 3.0 nul ucgassSnbr Forbs Sandberg Bunchgrasses Annuals 17-22 cm 2-7 cm June May April NO NH 4 3 + - T. caput-medusae (plants m-2) 100 200 300 Removal plots removed Nothing a removed forbs Annual a removed forbs Perennial a removed Bunchgrasses b A trait based approach for managing invasives

• Conventional groupings encompass a wide range of trait differences

• Different traits likely influence different ecosystem properties

• Effective invasive plant management requires an understanding of traits allowing invaders to outperform natives Trait variation of desirable species • Do you want to: – maximize trait variation – maximize a trait

D A C B What traits should be considered?

• Relative growth rate (RGR) is a key Native grass trait to consider • Invasives often have a higher RGR • Seed → seedling stage –Plant size Invasive grass – Resource capture • Influences competitive interactions and survival Components of RGR

• RGR (mg g-1 d-1) has two components – Leaf area ratio (LAR, m2 kg-1), the amount of leaf area per unit total plant mass

– Net assimilation rate (NAR, g m-2 d-1), the rate of dry mass gain per unit leaf area

RGR (mg g-1 d-1) = LAR (m2 kg-1) x NAR (g m-2 d-1) Decomposition of LAR

Leaf area ratio (LAR, m2 kg-1), the amount of leaf area per unit total plant mass, can increase by: 1. Adding more leaf biomass • Leaf mass ratio (LMR) amount of leaf mass per unit plant mass 2. Making more leaf area per unit biomass • Specific leaf area (SLA) amount of leaf area per unit leaf mass

LAR = SLA x LMR Decomposition of NAR

•NAR (g m2 d-1) rate of dry mass gain per unit leaf area

• Is the net balance of: – Photosynthetic carbon gain per unit leaf area minus carbon loss through respiration

– Influenced by how efficiently plants use nitrogen (leaf N productivity) and how much N is allocated to leaves. Traits driving RGR variation

SLA -1 (m2 kg ) LAR -1 (m2 kg ) LMR RGR (g g-1) (mg g-1 d-1) NAR (g m-2 d-1) Leaf N productivity (g leaf g N-1 d-1)

Leaf N concentration (g N m-2) Approach

• Use model to examine RGR traits in 3 invasive annual grasses, 3 perennial bunchgrasses, 6 invasive forbs, 6 desirable forbs

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-1 -1 RGR variation among grasses

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-1 -1 RGR variation among forbs Traits driving RGR variation

InvasiveInvasive vs. desirable vs. desirable forbs grasses

SLA -1 (m2 kg ) LAR -1 (m2 kg ) LMR RGR (g g-1) (mg g-1 d-1) NAR (g m-2 d-1) Leaf N productivity (g leaf g N-1 d-1)

Leaf N concentration (g N m-2) Toward trait-based management of invasives

• This involves identifying: 1. The specific ecosystem property or processes that we want to manage/ traits of the invader

2. The traits likely to have the largest impact on the property or processes

3. Trait variation and abundance in your desirable species pool • May only need to consider a handful of traits to maximize invasion resistance Traits to consider in desirable species pool

1. Get biomass established and get it fast – Target species with high RGR • High SLA and high nitrogen productivity

2. Select species that differ in phenology

3. Select species that differ in root distribution Questions and comments