2008 Dry Creek Sesbania Monitoring Report

sesbaniaIntroduction

The Sacramento Area Flood Control Agency (SAFCA) conducted an invasive plant control program for red sesbania (Sesbania punicea)(Sesbania) in the Dry Creek watershed from 2004 to 2006. The project was known as the Dry Creek Watershed Red Sesbania Control Project, Phase I (Phase 1 Project). The Phase 1 Project was funded by a California Department of Water Resources Proposition 13 Flood Protection Corridor Program grant administered by SAFCA. Since 2007, the maintenance phase of the removal program has been funded through a partnership between SAFCA, Sacramento County, Placer County, and the cities of Sacramento and Roseville. The project is administered by Placer County Resource Conservation District. The goal of the project is to reduce the potential for flooding in Dry Creek and to improve wildlife habitat in the watershed. The objective is to continue to remove and control seedlings of Sesbania, anticipating a diminishing level of effort over time.

This report presents the results of the 2008 monitoring effort. Monitoring was conducted by Ramona Robison, a sole proprietor doing business as California Botany with the assistance of Rebecca Waegell in June and SAFCA staff in August and October. The 2008 Dry Creek Sesbania removal contractor was Agri-Chemical and Supply, Inc., of Salinas. Gary Omori, Agri-Chemical’s Salinas office Area Manager, directed the removal effort. Agri-chemical conducted two control “sweeps” of the watershed and monitoring was conducted before sweep 1, after sweep 1, and after sweep 2.

The contract performance criteria were:

Table 1. Annual Success Criteria
Year Anticipated Condition at Start of Work Year Success Criteria at End of Work Year Overall Goal
Year 1 (2008)
  • 10-30% cover in lower watershed
  • < 10% cover in upper watershed
  • Removal of 99% of red sesbania by October 15
  • Eradication of Red Sesbania
  • < 1% remaining in treatment area at end of program

Methods

In 2008, the Dry Creek Sesbania monitoring program changed to meet requirements of grants and to provide better information on the condition of the infestation. In previous years a series of over 50 monitoring photographs were taken throughout the watershed. These photographs were useful during the early phases of the project when large shrubs were being removed, creating obvious “before and after” photographs. However, for the past few years the emphasis of control work has been on seedling removal which is not as easily monitored using photographs alone. The performance criteria for the project is removal of 99% of the Sesbania cover, and a quantitative means of assessing cover before and after treatments was needed.

Monitoring locations are also listed in Table 2.
Figure 1. 2008 Dry Creek Red Sesbania Monitoring Locations

We monitored the Sesbania infestation in six locations, collecting data on four 1 meter square quadrats at each location. Sampling locations with sand bars exposed during low flows were chosen to represent the upper, middle, and lower watershed (See Figure 1, above, and photographs in Appendix A [PDF*, 3 MB]). Several of the locations in the upper watershed (Royer Park in Roseville and downstream of Walerga Road) had few Sesbania plants, but were chosen to represent the condition in that portion of the Dry Creek watershed. Our choice of quadrat locations within the sandbar was also biased — we tried to choose quadrats with at least one live or dead Sesbania plant in them, even if the majority of the sandbar was free of Sesbania plants. This resulted in a higher cover classification than if randomly placed quadrats were used. However, the sampling unit was really the entire sandbar and the Sesbania occurring there was the focus of the monitoring effort. Permanent quadrats were also not chosen because of the dynamic nature of the river system.

Ground is lush with Sesbania.
Before Sesbania Treatment 6-21-08
Ground is bare where treatment was completed.
After Sesbania Treatment 10-7-08

During monitoring visits we took photographs of each quadrat and photographed a six foot tall pole marked off in one foot intervals to record overall vegetation height. We collected percentage cover data in each quadrat for live Sesbania alone and for all other live plant species present. The cover classes used are listed in Table 2. We counted all live Sesbania plants in the quadrat and measured the height of 10 plants to determine mean height per quadrat.

Gary Omori and Rich Gresham.
Gary Omori and Rich Gresham

The first monitoring visit was completed on June 21. We started at the top of the watershed in Granite Bay and traveled downstream to Rio Linda. For the second and third monitoring visits we started at Hansen Ranch at the bottom of the watershed and worked upstream. Agri-Chemical conducted their first sweep July 15–23 and our monitoring took place on August 11. Agri-Chemical’s second sweep was conducted September 8–12, and the final monitoring visit was completed on October 7. A final field meeting “walk-through” was held October 23 and was attended by Gary Omori, Ramona Robison, Rich Gresham (Placer County RCD), and Charlotte Kimball (Hansen Ranch Manager).

Results and Discussion

Photographs of the “before and after” condition of the Sesbania infestation in Dry Creek and its tributaries are presented in Appendix A [PDF*, 3 MB]. The table below summarizes the cover classes observed in June (before) and October (after). June and October values are presented, though a complete data set is available for the August monitoring visit. Data sheets with all quadrat information are included in Appendix B [PDF*, 12.7 MB].

In June, the largest number of live Sesbania plants per square meter was at the SAFCA property north of Hansen Ranch where we counted 106 plants in one of our quadrats. During the October visit the largest number of live plants observed in any of the quadrats was three and in many cases there were no live Sesbania plants in the quadrat.

The cover class information presented in Table 2 presents the highest and lowest cover classes observed in the four quadrats at each monitoring location. It should be noted that sample locations within the monitored sandbar were not randomly chosen. An attempt was made to place each quadrat in a location with either a live or dead Sesbania plant. All locations had 5% cover or less in October with the exception of Roy Hayer Park. The lower portion of the sandbar at Roy Hayer which was sampled in June was flooded during the August and October monitoring visits, so a location upslope with a Sesbania plant was chosen. These were large plants growing within tall mature vegetation which had been missed in previous sweeps. One of the quadrats in that location had between 5 and 25% cover of Sesbania due to the presence of two large plants. When live Sesbania plants were observed during monitoring visits we measured them and then pulled them by hand. There were so few plants remaining in the October visits that we were able to remove all live plants in the six monitoring locations. Throughout the monitored areas of Dry Creek and its tributaries less than 1% Sesbania cover remained in October.

Table 2. 2008 Dry Creek Sesbania Monitoring Data Summary
Monitoring Location June Cover Classes October Cover Classes June Mean Number of Plants per Meter October Mean Number of Plants per Meter Notes
Hidden Valley, Granite Bay 2, 3, 3, 6 0, 0, 0, 1 12 0.25 Only 1 live plant observed in quadrats which was removed
Royer Park, Roseville 1, 1, 2, 3 1, 1, 1, 2 2 1.5 Few plants observed
Walerga Road, Placer County 2, 2, 2, 2 0, 0, 1, 1 3.5 0.5 Few plants observed
Gibson Ranch, Elverta 3, 3, 3, 3 0, 1, 1, 2 12.5 1.25 Lower sandbar partially flooded
Roy Hayer Park, Rio Linda 3, 3, 4, 5 2, 3† 16.8 1.5† The October cover represents 2 large plants which were removed after monitoring.
SAFCA Property North of Hansen Ranch, Rio Linda 3, 4, 5, 5 0, 0, 0, 2 72.5 0.5
Cover Classes: 0-1% = 1; 1-5% = 2; 5-25% = 3; 25-50% = 4; 50-75% = 5; 75-95% = 6; 95-100% = 7
† Monitoring location was different in August and October from the original June location.

In 2008 we collected information on the plant species associated with Sesbania for the first time. Many quadrats contained grasses, sedges (Cyperus spp.), rushes (Juncus spp.), willows (Salix spp.), knotweed (Polygonumspp.), fireweed (Epilobium spp.), mugwort (Artemesia douglasiana), beggar’s ticks (Bidens frondosa), and valley oak seedlings (Quercus lobata). Other non-native and invasive plants were also observed including Himalaya berry (Rubus discolor), plantains (Plantago lancelata and P. major), cut-leaf geranium (Geranium dissectum), cocklebur (Xanthium strumarium), sweet clover (Melilotus sp.), cudweed (Gnaphalium sp.), and Mexican tea (Chenopodium ambrosioides).

Two other invasive plants of note were observed. The first, Chinese tallow (Sapium sebiferum), was observed in Roseville at Royer Park. Seedlings were observed in one quadrat in June and two quadrats in October, indicating a viable seed source and presence of a seed bank in the area. This is not surprising since the adjacent City of Roseville parking lot is landscaped almost exclusively with mature Chinese tallow plants. The second invasive species of concern was Eucalyptus. Eucalyptus seedlings were observed in June and October on the SAFCA property north of Hansen Ranch. The monitoring location was near a mature Eucalyptus grove, although Eucalyptus do not usually produce seedlings in the Central Valley.

Conclusions

The 2008 treatment year was successful in removing 99% of the germinated Sesbania population. The contractor also removed all Sesbania pods from the floodway, preventing future germination of those seeds. Since the project started in 2004 the focus has been on removal of upstream seed producing Sesbania plants, and given the reduction in seed production the seedbank should continue to decline over time. While results this year are promising, treatments must continue until the population is reduced to low levels. The size of the Dry Creek Sesbania population increased with the heavy rainfall in 2006 due to high water flows bringing seeds from low-flow channel sediments up onto the upper floodplain where they germinated far from the channel. Therefore the level of treatment effort needed in high rainfall years is expected to increase. With the type of data collected in 2008 it will be possible to compare the Sesbania percentage cover and seedlings per square meter in order to determine if the amount of seed germinating from the seedbank is decreasing over time. GIS location data collected in 2008 will also allow us to determine if the spatial extent of the population is decreasing.


Report prepared by: Ramona Robison, Ph.D., California Botanical Surveys and Tours, 1925 Meer Way, Sacramento, CA 95822.