sagebrush seedling recruitment following tebuthiuron application

Sagebrush seedling recruitment following

tebuthiuron applicationSara Germain, Rebecca Mann, Kari Veblen, Tom Monaco

Dept. of Wildland Resources, SURCO, NRCS CIG, Utah Agricultural Experiment Station, USDA-ARS Forage and Range Research Lab.

Goals1. Work with ranchers to increase forage for livestock.

2. Determine amount of shrub reduction in response to treatments

3. Evaluate how these responses vary with Ecological Site

Ecological Site-Based Management

Cedar Fort: Snakeweed Gutierrezia sarothrae

Birdseye: Rubber Rabbitbrush Ericameria nauseosus

Bear Lake: SagebrushArtemisia spp.

Park Valley: GreasewoodSarcobatus vermiculatus

Study Area

Two Ecological Sites per ranch

Bear Lake Site SpecificsEcological Site: Upland Stony LoamSoils: Lonjon Silt LoamElevation: 2225mTemperature: 6 C Precipitation: 305-406mm

Shrubs

Wyoming Big SagebrushBlack SagebrushRubber RabbitbrushGreen RabbitbrushBitterbrushSaskatoon Serviceberry

Grasses/Forbs

Wheatgrass Needle + ThreadPrairie Junegrass LupineBuckwheatArrowleaf BalsamrootAster

What is tebuthiuron?Soil active herbicide used to kill mature shrubs

How was it applied?Flew on pellets in fall 2012 – tebuthiuron 20P (2.5 lbs/ac)

Tebuthiuron and Sagebrush

Research Questions1. How does tebuthiuron affect young Sagebrush? 2. Does tebuthiuron affect Sagebrush seedling emergence?

Transect Map

Sagebrush density by age class: dead, mature, young • 1 Summer after treatment July 2013• 2 Summers after treatment July 2014

Seed rain trap – capture seed from this year• Autumn October – Nov 2013• Winter/Spring December – May 2014

Seed bank samples – capture seed from previous years

Sampling

Grow-out trialsGrew 200 sub-samples per trial (3 trials) in USDA greenhouse, counted and identified seedlings as they emerged (n=40 per trial)

• 2 Seed rain – sagebrush only

• 1 Seed bank – sagebrush, shrubs, forbs, grasses

Results – DensityAt the ranch...• Mature sagebrush decreased• Young sagebrush increased

Why?• Mature sagebrush is killed, opening new

niches for young sagebrush to grow• Application rate may be too low to kill

young plants

2013 20140

5

10

15

20

25

30

35

40

Sagebrush Density after Tebuthiuron Treatment

Young

Mature

Year

Mea

n N

umbe

r of S

ageb

rush

In the greenhouse...• Fewer Sagebrush seedlings

emerged from treated samples than control samples

Why?• Higher mortality of mature

sagebrush means fewer reproducing plants

• Is tebuthiuron reducing the viability of seeds from plants in treated areas?

Results - Seed Rain

Results - Seed BankIn the greenhouse...• No differences in seedling emergence (sagebrush, forbs, or grasses).

Why? • Viability of seed bank doesn’t seem to be affected by treatment.

Tebuthiuron and Sagebrush Management

On an Upland Stony Loam E.S:• Initial reduction of mature Sagebrush is effective

• Success may be offset by the failure to target reestablishment mechanisms

• Repeated applications, or use with other management tools, likely necessary to keep sagebrush densities low over time: this may be more costly

AcknowledgementsMonty Weston Property OwnerJustin Williams Field AssistanceRebecca Mann Graduate Student AdvisorKari Veblen Faculty AdvisorTom Monaco Experimental Design