EFFECTIVENESS AND LONGEVITY OF BUFFELGRASS TREATMENTS IN SAGUARO NATIONAL PARK Molly Hunter Assistant Research Professor Northern Arizona University, School of Forestry [email protected]

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

Three consecutive treatments Three consecutive treatments Two consecutive seasons Two consecutive seasons One skipped season One skipped season

Treatment type

Chemical Chemical + manual

Number of patches

15 11

Description

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

Chemical Chemical + manual Chemical Chemical + manual 28 15 15 10 Two herbicide treatments occurring in consecutive seasons.

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

Two herbicide treatments occurring in nonconsecutive season (one winter or summer season skipped) 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 (m 2 – 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

120 a a 100 ab b 80 60 40 20 0 Three consecutive trts Two consecutive trts One skipped season Two skipped seasons

Results

• Current buffelgrass coverage and density were lower in manual + herbicide treatments compared to herbicide only 9 1 0 3 2 8 5 4 7 6 1,6 1,4 1,2 1 0,8 0,6 0,4 0,2 0 Chemical only Manual and Chemical Chemical only Manual and Chemical

Results

•

Percent change in patch size was lower on south facing aspects

120 a ab a 100 b 80 60 40 20 0 North East South West

Results

• Current buffelgrass density and coverage were higher on south-facing aspects 1,5 1 0,5 0 3,5 3 2,5 2 a North ab b a East South

Dominant aspect

West 12 10 2 0 8 6 4 a North b ab a East South

Dominant aspect

West

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