1. Control methods for invasive species on Mima mounds at Turnbull National Wildlife Refuge, WA Brandy K. Reynecke and Rebecca L. Brown
Significance
Invasive plant species negatively impact the ecology of rangeland and prairie ecosystems by forming monocultures, outcompeting native plant species for resources and reducing the abundance of plants suitable for forage. The Channeled Scablands of eastern Washington has patchy distributions of rangeland and prairie which are dotted with geologic anomalies called Mima mounds. These mounds are aggregations of topsoil on basalt bedrock or glacial alluvium and provide habitat for plants during the summer when the shallow soiled inter-mound areas cannot. The mounds have been invaded by a multitude of winter annual grasses and invasive forbs resulting in a reduction of quality forage for cattle and wild life . Broad scale control of invasives, that also maintains natives, is difficult on the mounds and may require a combination approach. This study combines common techniques such as herbicide and native seed addition with experimental techniques . The experimental techniques we used for the control of invasive winter annual grasses are soil amendment with carbon as sucrose and a phytotoxic rhizobacterium Pseudomonas fluorescens D7 that specifically targets invasive annual grasses ; for the control of Linaria dalmatica we used a stem boring weevil Mecinus janthinus. It is necessary to restore the native vegetation on the mounds to ensure the continued availability of forage as well as preserve native plant species and communities.
Objective
Our goal is to test a combination of invasive species control and native restoration techniques on Mima mounds at Turnbull National Wildlife Refuge.
Experiment 1
Hypotheses: (make more specific)There will be a significant reduction in percent cover and stem count of invasive grasses due to treatments.
Methods:
Surveyed m2 vegetation plots summer 2009 (recorded species percent cover and stem counts of invasive grasses in a 400 cm2 subplot in a corner of each plot)
Applied fully factorial combinations of techniques across two substrates (alluvium and basalt) in the summer and fall 2009 (16 treatments; 4-11 replicates) and include:
-50 g sucrose/plot applied three times in ~three week intervals during rain events beginning the second week of June
(McLendon and Redente 1992; Paschke et al. 2000)
-140 ml Plateau herbicide/m2 applied mid November (0.75% conc., spot treatment rate)
-3 g seed/plot (Newman and Redente 2001); seed mix was Idaho fescue (Festuca idahoensis) and
Blue bunch wheat grass (Pseudoroegnia spicata)
Study Site
Basalt
Alluvium
Treatment effects on invasive annual grasses were analyzed using GLM in SAS.
Treatment effects on native and exotic percent cover and species richness were compared using ANOVA with Tukey pair wise comparisons. Kruskal-Wallis tests were used for non-normal data. (Only significant results are shown.)
Did the treatments significantly reduce the abundance of invasive grasses?
Was there an interaction between effects of substrate type and treatment on invasive grasses?
Did substrate significantly affect species richness?
Herbicide decreased cover of Bromus tectorum, B. commutatus, Ventenata dubia (P = 0.001) and all grasses cumulatively (P = 0.04). It also decreased over all grass stem counts (P = 0.02).
There was a greater reduction in both exotic and native species richness on basalt as compared to alluvium (p < 0.001).
Herbicide reduced the abundance of Ventenata dubia (P = 0.01) and Bromus tectorum (P < 0.001) more on the alluvial substrate than on basalt.
Experiment 2
Hypothesis: Doubling M. janthinus population will decrease L. dalmatica abundance.
Experiment 3
Hypothesis: Pseudomonas fluorescens D7 will decrease invasive annual grass abundance.
Discussion
Experiment 1:
Herbicide was the only technique that reduced abundance of invasive annual grasses and it is more effective on mounds underlain by alluvium than basalt, however it also killed most native species.
Carbon soil amendments had little effect possibly because the amount of sucrose used was insufficient or because applications were not applied at the right time.
Native seed addition has had no effect to date, however it typically requires >1 year for natives to establish.
Total species richness decreased overall (perhaps due to climatic differences from ) and was significantly more pronounced on basalt, possibly due to recruitment limitation.
Experiment 2:
Mecinus janthinus did not reduce the abundance of Linaria dalmatica possibly because the pre-existing population is having the maximum effect or because one growing season is an insufficient amount of time to see a significant reduction.
Experiment 3:
Pseudomonas fluorescens D7 did not significantly reduce the abundance of invasive annual grasses possibly because ambient air temperatures were too low at time of application or because one growing season is insufficient to see a significant result.
Future implications
When developing restoration plans on Mima mounds substrate must be taken in to account. The long term effects of these treatments will be tested in future studies.
Methods:
Surveyed 35 1 m2 vegetation plots summer 2009 ( recorded species percent cover and stem counts of mature L. dalmatica plants.)
Caged plots to contain insects
Applied 20 adult insects per plot in July; !doubling the existing population.
Herbicide, sucrose, and native seeds added in same concentrations and at the same time as in experiment 1 ( not fully factorial)
Treatment effects on stem count and percent cover of L. dalmatica were analyzed using ANOVA with Tukey pairwise comparisons and Kruskal –Wallis tests
(Only significant results are shown.)
Methods:
Surveyed 14 1 m2 vegetation plots in the summer of 2009 ( recorded species percent cover and stem counts of invasive grasses.)
Plots fenced
108 cells P.f. D7/ m2 (10 gal/ acre) in aqueous solution as per WSDA EUP(experimental use permit) 9025 applied in December.
Treatment effects on stem count and percent cover of invasive grasses were analyzed using paired t-tests0
M. janthinus did not significantly decrease L. dalmatica
P. fluorescens D7 did not decrease invasive annual grasses.
Acknowledgements: We thank the U.S. Department of Fish and Wildlife and the EWU biology department mini grant for funding this project. We also thank Mike Rule, TNWR employees and all of the AmeriCorps volunteers who lent intellectual and manual support. Thanks to Dr. Anne Kennedy of WSU and Chris Wend of Northwest Agricultural Products for providing and applying the P.f.D7, Jessica Bryant for help with the design and execution of these experiments., and field assistants Trenton Reynecke, Cara Hulce, Jen Grimes, Brittany Davidson and Holly O’Conner for all of the hot sweaty hours spent out on the prairie.