Effectiveness and longevity of buffelgrass treatments in sAguaro National Park

EFFECTIVENESS AND LONGEVITY OF BUFFELGRASS TREATMENTS IN SAGUARO NATIONAL PARK

Molly HunterAssistant Research ProfessorNorthern Arizona University, School of ForestryMolly.hunter@nau.edu

Objectives• Assess the effectiveness of different buffelgrass control

treatments (i.e. manual pulling, herbicide application)

• Determine how buffelgrass treatment effectiveness is impacted by factors such as treatment timing, treatment frequency, and site characteristics

Saguaro National Park• Examined treatments from 2006

– 2010• Data collected in 2010• Two types of treatments

• Herbicide only• Manual pulling followed by herbicide

• Two treatment seasons• Winter (October – May)• Summer (June – September)

Rincon Mountain District Tucson Mountain District

Treatment regime Treatment type

Number of patches

Description

Three consecutive treatments

Chemical 15 Three herbicide treatments occurring in consecutive seasons.

Three consecutive treatments

Chemical + manual

11 Three treatments (one manual followed by two herbicide) occurring in consecutive seasons.

Two consecutive seasons

Chemical 28 Two herbicide treatments occurring in consecutive seasons.

Two consecutive seasons

Chemical + manual

15 Two treatments (one manual followed by one herbicide) occurring in consecutive seasons.

One skipped season Chemical 15 Two herbicide treatments occurring in nonconsecutive season (one winter or summer season skipped)

One skipped season Chemical + manual

10 Two treatments (on manual followed by one herbicide) occurring in two nonconsecutive seasons (one winter or summer season skipped)

Two skipped seasons Chemical 12 Two herbicide treatments occurring in nonconsecutive seasons (one winter season and one summer season skipped)

Other variables• Rainfall (total rainfall 1 month prior to treatment)• Aspect (N, S, E, W)• Time since last treatment (months)• Slope (%)

Response variables• Current density (individuals m-2)• Current coverage (m2 – percent cover X patch size)• Percent change in patch size (time of first treatment

compared to summer 2010)• Percent change in density• Percent change in coverage

Statistics• Categorical variables

• Non-parametric tests (van der Waerden chi square, Wilcoxon test)• Continuous variables

• Spearman’s correlation

Results• Change in patch size was lowest when two seasons were skipped

• No other variables impacted by treatment regime

0

10

20

30

40

50

60

70

80

90

100

Cha

nge

in p

atch

siz

e (%

) ab a a

b

Results• Current buffelgrass coverage and density were lower in

manual + herbicide treatments compared to herbicide only

Chemical only Manual and Chemical0

0.2

0.4

0.6

0.8

1

1.2

1.4

Cur

rent

buf

felg

rass

indi

vid-

uals

m-2

Chemical only Manual and Chemical0

1

2

3

4

5

6

7

Cur

rent

buf

felg

rass

cov

erag

e (

m2)

Results• Percent change in patch size was lower on south-facing aspects

North East South West0

20

40

60

80

100

120

Cha

nge

in p

atch

siz

e (%

)

a a ab

b

Results• Current buffelgrass density and coverage were higher on

south-facing aspects

North East South West0

1

2

3

4

5

6

7

8

Dominant aspect

Cur

rent

buf

felg

rass

cov

erag

e

b

ab

a a

North East South West0

0.5

1

1.5

2

2.5

Dominant aspect

Cur

rent

buf

felg

rass

indi

vid-

uals

m2 b

a

ab

a

Results• Percent slope was negatively correlated with change in

patch size (-0.24) and change in density (-0.30)

• Percent slope was positively correlated with current density (0.32) and current coverage (0.35)

Results• Rainfall was positively correlated with percent change in

coverage (0.27)

• Rainfall was negatively correlated with current density (-0.23) and current coverage (-0.20)

Uncertainties• Time since last treatment was not significant, but time

frame of study was short

• Distance to roads/trails/drainages, soil type, and temperature not assessed

• Influence of original patch size, cover and density not assessed

Conclusion• Most plots showed reductions in patch area greater than 90%

• Skipping two full treatment seasons (one winter and one summer) may result in less successful control of buffelgrass

• Combination treatments may be slightly more effective than herbicide only treatments

• Buffelgrass abundance measures were consistently higher on south-facing aspects

• Buffelgrass treatments were less effective on steep slopes

Acknowledgements• Dana Backer and Perry Grissom (SNP)• Leigh Perry (UA)• NPS Fuels Reserve Fund