1. Vanessa Tobias, Giselle Block, Emilio Laca
Fine-scale predictions of perennial pepperweed invasion in a brackish tidal marsh
Vanessa Tobias, Giselle Block, Emilio Laca

2. Perennial Pepperweed Lepidium latifolium LELA

3. Creates monocultures forestryimages.org
Displaces adorable natives & swallows grazing animals
forestryimages.org

4. Displaces marsh animals. Here: salt marsh harvest mouse
water.ca.gov

5. Spreads by Rhizomes and Seeds
Not only does pepperweed live in a variety of conditions, it has a variety of mechanisms for spreading
Seeds float and can germinate in saline conditions
Spread by rhizomes and vegetative parts seems to be the most common method of spread in wet areas, though.

6. Marshes are at high risk for pepperweed invasion
Vanderhoof et al. 2009

7. Marshes are at high risk for pepperweed invasion
Vanderhoof et al. 2009

8. Management Needs for LELA
Efficient search models
Eradication plan for wetlands
Right now, recommendations for eradicating pepperweed aren’t very practical for marshes.
Methods for treatment in uplands, rangelands aren’t appropriate for wetlands- mowing with heavy equipment and grazing isn’t an option.
For wetland managers, the best defense is to find new invasions in the early stages. Since no one has unlimited funds or personnel, we focused on figuring out ways to make searching for new invasions as effective as possible.

9. San Pablo Bay NWR Sacramento San Pablo Bay Suisun Bay Sacramento Delta
Golden Gate
This is a reference map of San Francisco Bay that shows where I’m working.
For this project, I’m working with the staff of San Pablo Bay National Wildlife refuge to figure out where pepperweed invasions are most likely.
The refuge is on the north side of San Pablo Bay and it consists of saline tidal marsh. It’s a unique area for studying pepperweed because most of the research that has been done is in freshwater wetlands and rangelands.
San Francisco Bay

10. Project Area Ag Land Bay 4 km 10 km
This is a closer view of the section of the refuge where pepperweed was mapped. This is actually a bit bigger than the mapping area- the mapping was generally in the dark brown areas near the bay. This shows that the marsh is sandwiched between agricultural land and the bay.
Bay
10 km

12. Mapping of LELA patches by field crews before and after spraying
Ag Land
Bay

15. Explanatory variables used in the model
Vegetation
Disturbance
Channels, shoreline, & levees
Elevation (LiDAR)

16. Channels, shoreline, & levees
Elevation (LiDAR)
Vegetation
Disturbance
LELA Patches

17. Map of predicted probability of invasion
Ag Land
Bay
Deviance Explained = 27%

18. A practical application of modelled probabilities:
Maps identifying potential habitat
LELA Present in 2005
Potential Habitat
Search Area
Ag Land
Bay
This is the practical use of the modelling probabilities. This map shows places where the model predicts pepperweed is likely to establish in green. The yellow spots are places that actually had pepperweed in the 2005 mapping. The patch sizes are exaggerated so the colors show up.
I really like this map for a couple of reasons. First, it’s a practical application of the model. This is something that the staff can use to focus their searches. They can see where the patches were, and where new patches are likely to establish. They can also see that there are large sections of the refuge that probably don’t need to be searched as often. Second, it shows why the model doesn’t do well numerically- there are many places that have reasonable habitat for pepperweed that haven’t been invaded yet. These are important areas to check, but they show up as errors in the model.

19. True Positives
False Positives
Search Area
False Negatives
Ag Land
Bay

20. Potential habitat that hasn’t been invaded yet shows up as “false positives” in our model
True Positives
False Positives
Search Area
False Negatives
Ag Land
Bay

21. New patches mapped in 2010 as a test case for the model
New LELA Invasions 2010
Potential Habitat
Search Area
Ag Land
Pepperweed was also mapped in 2010 and the model predicted most of the new patches. That’s a pretty exciting thing because it shows that if managers used this map, they would have found most of the new patches in the early stages. That’s going to be important for controlling invasions in the future.
Bay

22. Focus search and efforts for LELA on levees and channel berms.

23. Number of Patches
Percent Cover of Pepperweed

24. No Spray
Spray

25. Herbicides are an effective control for LELA in areas where mechanical control is impractical.

26. Questions? Vanessa D. Tobias vtobias@ucdavis.edu Postdoctoral Scholar
University of California, Davis
Department of Plant Sciences