Objectives
Catherine Brett¹, Patrick Yin², Kyle Zhang², Hamsavardhini (Anu) Thirunarayanan², Zonghuan (Jason) Li²
¹CuriOdyssey, Sr. Educator and Science Research Manager
²San Mateo High School
Manual Removal and Herbicide Treatment for Maximum
Limonium ramosissimum Reduction
Background
Limonium ramosissimum (Poir.) Marie (1), also known as Algerian sea lavender or LIRA, is a perennial herb native to the western Mediterranean. Introduced into the San Francisco Bay Area where it has proven to be invasive, LIRA has out-competed native plants including Sarcocornia pacifica (perennial pickleweed) and Distichlis spicata (coastal salt grass) in salt marshes (2). LIRA forms dense, nearly monotypic mats and directly competes with native pickleweed (3), which provides habitat for the endangered salt marsh harvest mouse, Reithrodontonmys raviventris (4).
Soon after dense patches of LIRA were discovered in the San Francisco Estuary in 2006, researchers began to map the extent to which LIRA has spread and assess its invasion potential. More research revealed that a single large LIRA plant can yield as many as 17,000 seeds (3) and thrives in the higher marsh zones from mean high water to mean higher high water zones in low salinity conditions (5). Therefore, the seed bank under a mat of LIRA has the potential to provide an abundant supply of seeds for new recruitment despite diligent hand removal efforts.
In June 2016, funded by a grant from the National Fish and Wildlife Foundation, the California Invasive Plant Council (Cal-IPC) treated the LIRA at Coyote Point Park with an herbicide application, a combination of imazapyr and glyphosate, two active ingredients that have shown previous success (6). In October 2016 following the herbicide application, observations of its effectiveness on LIRA revealed mixed results. Given the herbicide efficacy we want to understand how best to maximize LIRA reduction with a combination of manual removal and herbicide treatments, while trying to minimize costly hand removal efforts.
Initially, LIRA percent coverage in the control and treatment 1 stays almost exactly the same as both sharply decrease to the lowest point at month 3. This indicates that both the control and treatment 1 reduce LIRA with the same effectiveness up until month 3.
After month 3, the percent coverage of the control and treatment 1 starts to gradually increase and diverge slightly. Specifically, at month 6 and 9, the treatment 1 plots have a lower percent coverage than the control plots. This indicates that treatment 1 is more effective than the control at reducing LIRA regrowth up until the 12 month mark. After 12 months, the difference in percent coverage between the control and treatment 1 ceases to be statistically significant. This means that treatment 1 is only more effective than the control at reducing LIRA regrowth in the short-term span of one year.
Since not all plots randomly selected for treatment 2 had large (≥15 cm) LIRA plants, the treatment was applied to only 7 of 10 randomly selected plots, causing the comparison of all treatment data to be difficult and insufficient for analysis. A well established infestation of large LIRA plants will be necessary to answer this question in future research.
Anecdotally, we noticed that as the small individual LIRA plants grow larger, they fuse together into larger LIRA plants. This may be an example of inosculation in LIRA.
Image of Limonium ramosissimum
Jason Li and Patrick Yin holding a LIRA plant
Conclusions
Acknowledgments
The purpose of this experiment is to help determine the best methods for local reduction of LIRA at Coyote Point Park in San Mateo, CA. In this study, we sought to investigate the impacts of different levels of manual removal effort after an herbicide application to determine if the maximum LIRA reduction is achieved by manually removing all LIRA plants, or whether it is equally effective to remove only the large LIRA plants. The results of this experiment will serve to inform future management strategies and LIRA removal efforts at Coyote Point Park and potentially the greater San Francisco Estuary.
Plot 27: Treatment 1
Plot 8: Control
Drew Kerr, Treatment Program Manager, Cal-IPC; Kevin Shoban, Science Educator and Photographer, CuriOdyssey; Elsa Valenzuela, SFSU Ecology, Evolution and Conservation Biology Candidate, 2019; Bryan Holmes, Science Educator, CuriOdyssey; Beth Kracum, Science Educator, CuriOdyssey; Róisín Altreuter, Science Educator and Conservation Coordinator, CuriOdyssey; Lu Yin, Data Scientist, Sphere Institute; Leigh Simpson, Volunteer Photographer, Jacob George SMC Ranger; Sabrina Jin; The Moore Foundation Volunteers; St. Matthews Episcopal School 6th grade 2018; San Mateo County Parks
Preliminary Results
Initially, before herbicide application, the LIRA percent coverage between the control and treatment 1 are very similar at 29.410% and 28.809%, respectively. LIRA percent coverage drops dramatically after herbicide application, reaching the lowest point at month 3 at 0.995% for the control and 0.717% for treatment 1. After that, LIRA percent coverage gradually increases. The LIRA percent coverage at month 15 is about one-third that of the initial LIRA percent coverage. LIRA percent coverage in treatment 1 is lower than in the control group. The difference between the treatment 1 and the control at 6 months and 9 months is statistically significant.
Thirty, square meter plots were randomly selected for one of three treatments, 10 plots per treatment. Initial data were collected one day prior to herbicide application. All experimental plots received herbicide application before hand pulling treatment. The three treatments were as follows – Treatment 1: Hand pull every LIRA plant. Treatment 2: Hand pull only large LIRA plants (≥15 cm). Treatment 3: Control, herbicide application only, no hand removal. Images of experimental plots were taken before herbicide application and every three months following treatments for the next 24 months.
Data were captured from each image using Clipping Magic and GNU Imaging Manipulation Program, (GIMP), both available for free on the internet. Clipping Magic is a website that allowed us to isolate the live LIRA (≥50% green) or isolate the necromass (≤50% green, distinguishable parts with visible roots and leaves). After isolating the selected region in the image, percent coverage was captured using GIMP which counts the total number of pixels in the image and the pixels in the selected region and produces a ratio.
At each 3-month plot point, we conducted an ANOVA between the plot percentage of treatment 1 and treatment 3. The data taken for treatment 2 were insufficient for analyses.
Date | Initial | Month 0 | Month 3 | Month 6 | Month 9 | Month 12 | Month 15 |
Control (Avg % Coverage) | 29.410% | 3.662% | 0.995% | 3.139% | 3.884% | 6.914% | 9.163% |
Treatment 1 (Avg % Coverage) | 28.809% | 4.595% | 0.717% | 0.833% | 0.688% | 3.774% | 6.875% |
P-Value from ANOVA | | 0.7999 | 0.6889 | 0.02419 | 0.01213 | 0.05443 | 0.3379 |
References
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Materials and Methods
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