With many more non-native species than native species, the Delta is considered the most invaded estuary in the world. Climate change is expected to make conditions more favorable for invasive species at the expense of native species. At the November meeting of the Delta Stewardship Council, Delta Lead Scientist Dr. Laurel Larsen’s Science Spotlight focused on the most invasive marsh plant species in the Delta, phragmites australis, or the common reed. The plant species is native to Europe, but a rampant invader in marshes across the US.
In the Suisun Marsh, it’s particularly problematic as its rapid expansion has threatened biodiversity and the quality of habitat for fish and wildlife. The invasion of phragmites presents an interesting social-ecological issue due to the patchwork of land ownership in Suisun Marsh among duck clubs, other private owners, and public entities. It’s also challenging in that parts of the marshland are open to tidal exchange, and levees with controlled inflow surround other parts; herbicides are restricted in the stands that are open to tidal exchange because of the possibility of dispersal further into the estuary and the possibility of threatening endangered species habitat.
The Suisun Resource Conservation District has a program that incentivizes individual landowners to treat stands of phragmites with herbicide where they can. Still, there’s little data to show whether or not that program has been effective.
One of the larger projects funded by the Delta Stewardship Council under the 2021 proposal solicitation was to a research team led by John Takekawa of the Suisun Resource Conservation District. His team is using a participatory collective approach to studying the social and ecological dimensions of phragmites invasion and management in the Suisun Marsh. They will be establishing and evaluating an integrated management approach for control, implementing a monitoring program, assessing landowner perceptions and their ability to engage in different actions for controlling phragmites, soliciting their technical input, and ultimately developing a regional coordination plan.
The paper, Invasive vegetation mapping from publicly available data shows extensive spread of Phragmites australis in Suisun Marsh, is the first paper to be published from that project. The paper addresses the challenge that it can be very difficult to respond effectively to phragmites spread in a timely manner because there’s not much data on where phragmites is, how quickly it is spreading and has spread, and whether the rate of spread in particular locations might be linked to management strategies that are being applied in those locations.
Currently, the Department of Fish and Wildlife publishes vegetation maps for Suisun Marsh every three years. The maps are meticulously developed by experts in a time-consuming process that depicts the distribution of vegetation over the previous three years. For this study, the research team used publicly available aerial photography collected by the US Department of Agriculture and used artificial intelligence to train the computer to recognize patches of phragmites from the aerial imagery. The aerial photographs are available every two years, so the frequency is slightly better than the previous vegetation mapping, but even more important, these maps can be generated almost instantly as soon as the images are available.
“The research team found that the strategy can identify phragmites patches at 90% accuracy, which is comparable to the expert-derived vegetation maps,” said Dr. Larsen. “When the research team applied their mapping technique to the record of available photographs, they found that phragmites has been expanding in Suisun Marsh more rapidly than has been reported anywhere else in the world. They suggested that some of the characteristics that are unique to Suisun might make it a particularly good habitat for phragmites to outcompete other species. This includes frequent drought when its expansion really seems to take off.”
However, Dr. Larsen said the story is not all bad. “They were also able to see that phragmites abundance has decreased in some areas within Suisun, particularly the impounded managed wetlands where it is likely that treatment has taken place, even though they don’t have specific historical data on where that treatment was. But that is some of the monitoring that will take place as part of this project. So going forward, the team will be able to combine this aerial photography approach for monitoring with the information that they’ll be collecting in order to assess the effectiveness of treatment.”
“The other thing that the team learned from their analysis is that the proximity of a land parcel to other parcels that already have phragmites makes that parcel highly likely to become invaded in the future, whether or not there’s a levee separating the two parcels,” she continued. “This high propensity for spread underscores the fact that it’s very important to coordinate control efforts regionally. And I will be staying tuned to see what progress the team is able to make in their goal to promote this regional coordination.”
DELTA SCIENCE UPDATES
The Salinity Management Workshop series will be held on March 26-27. This second workshop will focus on the human dimensions of salinity management. The first day will highlight the conceptual model of the impacts of different salinity management actions within the Delta and hear the results from a research team that’s been conducting interviews on different communities’ perceptions of salinity management and their impacts. The second day will focus on the results from new modeling tools that have been developed and what we’re learning from the new modeling tools in terms of what we might expect salinity distribution to be during future drought conditions under a limited subset of scenarios, including one that’s very much like the Delta adapts restoration scenario. The second day will solicit feedback on the visualizations of the results, what additional metrics are needed, and any perceived gaps.
“We anticipate that this workshop is going to be incredibly useful for staging the next steps in a collaborative, adaptive, participatory scenario planning process that will be taking place through externally funded research,” said Dr. Larsen. “The Council is going to be producing a white paper that summarizes some of the research science and modeling gaps that we learned about from this workshop series, as well as produces recommendations or scenarios that diverse communities would like to see run and how they would like those results to be communicated.”
The Delta Independent Science Board hosted a workshop on food webs on November 8. The workshop evaluated the degree to which the inclusion of foodweb interactions across different levels of the food chain could benefit and facilitate ecosystem management. One specific question was whether the available data and science can support the development of tools such as food web models and forecasting capabilities. It included presentations from scientists, managers, and stakeholders with a lot of diverse experience and food web dynamics, including elsewhere in the US.
“One of the things that I particularly appreciated was hearing from Zachary Emerson from the United Auburn Indian community on several panels. We learned about how United Auburn and Shingle Springs are really interested in establishing an indigenous ecology lab in the Delta and getting involved in some of this research. We also learned about the Coyote Crew that they have formed, which is an intertribal cultural ecosystem revitalization crew promoting indigenous burning to achieve multiple objectives, including improvement of food web dynamics. So that just underscored this growing emphasis that we have in the Science Program and in the Council to learn from indigenous communities and really include them in our planning and learning processes.”
The fall edition of the biannual Delta Breeze newsletter is now available. The theme of the newsletter is open science and the global movement to make scientific research processes and products accessible to all. INCLUDE LINK
