Summary of Pre- and Post-Project Vegetation Survey Results

Transcription

1 3921 East Bayshore Road Palo Alto CA tel fax Introduction Summary of Pre- and Post-Project Vegetation Survey Results Acterra Stewardship s San Francisquito Creek Habitat Restoration Project at Hopkins Creekside Park in Palo Alto was a two-year project funded by the Santa Clara Valley Water District to restore vegetation in Hopkins Park. Hopkins Park is a 1.5-mile linear open space area along San Francisquito Creek owned by the City of Palo Alto. This project focused on the 3,700 linear foot section of the park between Middlefield Road and Chaucer Street. The project site was in part chosen because the local neighborhood was already holding creekside restoration volunteer days and was enthusiastic about expanding this effort. The existing vegetation along this section of creek was typical of many urban streams in the region. The existing tree species include mature native trees such as Coast Live Oak, Buckeye, Elderberry, and Bay as well as many non-native trees species including invasive Tree-of-Heaven, Acacia, Privet and Eucalyptus. The primary native shrub in the understory is Toyon and there are several invasive shrubs including Cotoneaster, Italian Buckthorn, Privet and French Broom. At the beginning of the project, the understory was dominated by invasive Algerian Ivy with smaller quantities of Cape Ivy, Himalayan Blackberry, and Periwinkle. This project involved community volunteers in revegetating 2,500 linear feet of the creek bank. Volunteers cleared Algerian Ivy and other invasive plants manually and sheet mulched some areas- using cardboard with a layer of wood chips to suppress weeds. Native plants were then installed in many of the weeded and sheet mulched areas. Volunteers helped maintain planted areas by watering, weeding, and picking up trash. A baseline vegetation survey of the site was conducted, documenting existing species and approximate percentage of native versus non-native cover along the stream from Middlefield Road to Chaucer Street (0.7 miles, approximately 3,700 feet). The initial survey also provided data needed for prioritizing restoration reaches. The survey was repeated after project completion to evaluate success. This report summarizes and discusses these survey methods and results. Methods The pre-project survey was completed in July of 2013, and the post-project survey was completed after two years of revegetation work, in July The 3700 linear foot (ft) length of Hopkins Park was divided into 100 ft sections. For every section, a 100 ft long baseline was established parallel to Palo Alto Avenue and marked off. Using a random number generator, a number between 1 and 100 was determined for each 100 ft section, marked, and a transect tape was laid perpendicularly along the top of bank. Each transect was laid from the street curb towards the creek until the bank became too steep or too densely covered with poison oak to safely survey. A 3 square foot quadrat was placed on the downstream side of each transect at 10 ft increments until the end of the transect (unless a tree was obscuring the way, in which case, the quadrat was laid on the upstream end of the transect).

2 For every quadrat, vegetation was identified and measured at three levels: ground cover, mid-level and canopy. Ground cover was defined as any vegetation less than 3 ft tall and percent cover was determined for each identified species. Mid-level vegetation was defined as 3-15 ft, for which each species was identified and percent cover was estimated. Canopy was defined as vegetation over 15 ft tall. In the pre-project survey, a spherical densitometer was used to determine an average percent canopy cover at two separate locations for each transect, one at the beginning and one at the end. At each end of the transect, four canopy measurements were taken 90 to each other. Average percent canopy cover was calculated for each site and a list of trees contributing to the canopy made. Because canopy was not the focus of the project or likely to have changed in a two year project where large trees were not removed, we analyzed total canopy cover in the pre-project survey but not the post-project survey. Results The results are given for each vegetation level: understory (0-3 feet), midlevel (3 to 15 feet) and canopy (above 15 feet). The most significant result is that we successfully reduced Algerian Ivy percent cover from 48% to 14% in the understory, and to almost none (0.04% cover) in the midlevel. Instead of removing ivy in the canopy, we cut the vines at a level easy to reach so it lost its source of water and nutrients. Ivy in the canopy usually finds enough sun to flower and set fruit and seed that is moved by birds so it is especially important to control. Understory vegetation: Native understory started out very low (2% of total land) and non-native understory very high (57%) with the remaining bare soil or leaf mulch (41%) (see Figure 1 below). The postproject survey results summarized in Figure 2 below shows a doubling in native percent understory and a 70% reduction in Algerian Ivy. As shown in Figures 3 and 4, the native understory percent of total understory vegetation (not including bare soil/mulch) is up from 4 to 14%. Approximately 3,000 plants of 60 differing species were planted in the stream reach. The survey successfully documented some of this increase in diversity. The number of native understory species documented in the survey increased from 7 to 17 species. We believe the increase in native understory would have been significantly higher if the project had been carried out during non-drought years. We hope that the anticipated increase in rain events this year will contribute to increased native cover by spring. 2

3 Figure 1. Pre-project native vs. non-native cover. Algerian Ivy represented about 48% of the non-native species cover and 85% of total non-native plant cover. Figure 2. Post-project native vs. non-native cover. Native plant cover doubled over the project period. Native plant cover will increase and native mulch/bare soil will decrease as the young installed plants grow. 3

4 Midlevel Vegetation There is relatively little mid-level vegetation in Hopkins Park, less than 13% cover measured by our survey. The good news is the survey results show a decrease in non-native midlevel vegetation from 7% to 3% and an increase in the native midlevel vegetation from 5 to 10% of the total cover. Native percent cover of midlevel vegetation should continue to increase as the young shrubs planted in the last two years grow. Figures 3 and 4. Pre and Post-project native vs. non-native cover % of total vegetation, not total land area. Native diversity increased by 50% and native cover by almost 100%. The native species found as midlevel vegetation during the surveys were: Bay Laurel, Big Leaf Maple, Buckeye, Coast Live Oak, Elderberry, Holly Leaf Cherry, Poison Oak, Redwood stump/sprout, Toyon, Walnut, and Wild Cucumber. The non-native species found as midlevel vegetation during the surveys were: Algerian Ivy, Cape Ivy, Cotoneaster, French Broom, Italian Buckthorn, Oleander, Pittisporum, Plum, Privet, Tree of Heaven, Poison Hemlock and Smilo Grass. Oleander does not appear to be invasive, but has been planted in the park. The remaining species are all very invasive. Figure 5 and 6 are pie charts that show the percent of total vegetation for each native and non-native species. Native species pie slices have beveled edges so that the increase in native composition is visible. It is clear that we have reduced the dominant non-native and invasive shrubs and vines such as Ivy, Italian Buckthorn, French broom, and Privet. 4

5 Note: beveled (raised) sections correspond to native species Figure 5. Pre-project native and non-native percent of total midlevel vegetation. Non-native ivy, buckthorn, oleander and broom were the dominant weeds. Note: beveled (raised) sections correspond to native species Figure 6. Post-project native and non-native percent of total midlevel vegetation. Note: native Toyon, Coast Live Oak, Elderberry and Holly Leaf Cherry now dominate. 5

6 Canopy During the pre-project survey, canopy cover was analyzed at the street end and creek end of each transect. The average, minimum and maximum canopy cover for each end are shown in Table 1. The lists of native (11) and non-native (17) canopy species is in Table 2. Those nonnative species known to be invasive are marked with an asterisk. This project focused in the short term on improving understory and midlevel canopy, although in the long term, removed saplings of invasive trees and planted native saplings will have a positive impact on the ecosystem of the park. Table 1. Canopy cover: average minimum and maximum cover at each end of transect Street End of Transect Creek End of Transect Average 66% 73% Maximum 89% 95% Minimum 18% 34% Table 2. Canopy species found in Hopkins Park transects. Invasive trees marked with (*). Total of 11 native and 17 not native species. Native Canopy in Hopkins Park Coast Live Oak Box Elder Poplar Black Walnut Buckeye Bay Laurel Poison Oak Elderberry Redwood Toyon Holly Leaf Cherry Non-native Canopy in Hopkins Park Oleander Cotoneaster* Cedar Stone Pine* Linden Tree of Heaven* Acacia* Pyracantha Deodar Hackberry* Eucalyptus* Siberian Elm* Privet* London Plane Magnolia Olive* Casuarina* 6

7 Figure 7. Summary of notable changes. Algerian Ivy % cover decreased, while native groundcover % total vegetation and native understory diversity increased. There was an increase in native midlevel % of total vegetation. We project that native midlevel % total vegetation will continue to increase as the shrubs planted during the project continue to grow and reach midlevel height. Summary For the riparian ecosystem of Hopkins Park to be protected and enhanced it is important to increase native cover and diversity at all levels of vegetation: understory, midlevel and canopy. This project focused on removing invasive species at the lower two levels and planting plants that will eventually become cover at all three levels. The pre-project survey found the understory was 48% Algerian Ivy and the post-project survey showed we successfully reduced this to 14% over the entire 3,700 foot stretch of creek bank. Many areas were totally cleared and are now 0% ivy cover, however the survey transects were randomly placed, many passing through sections of creek bank where ivy has not yet been cleared. The native percent understory (not including bare soil and mulch) has increased from 4 to 14%. Native diversity has gone up substantially as 3,000 plants of 60 differing species were planted in the stream reach. The survey successfully documented some of this increase in 7

8 diversity. The number of native understory species documented in the pre and post surveys increased from 7 to 17 species. We believe the increase in native understory would have been significantly higher if the project had been carried out during non-drought years. We hope that the anticipated increase in rain events this year will contribute to increased native cover by spring. Much of the invasive midlevel vegetation was reduced, however until native cover is established, easily seeding species such as poison hemlock will come into cleared areas. The midlevel shrubs that are the most invasive include Italian Buckthorn, French Broom and Privet. The Hopkins Park ecosystem will also require diligence to control a fast spreading large perennial grass, Smilo Grass. This grass was introduced from Eurasia in the early part of the 1900s and has made significant inroads into riparian and wetland areas in the Bay Area. Due to our efforts, midlevel non-native vegetation decreased from 60% of the total vegetation to only 20%, and the percent native vegetation doubled from 40% to 80%. Our planting of midlevel species was not detected as mid-level cover by our survey as these plants have not yet attained midlevel species height. Therefore, midlevel native cover will increase more with time as several native species that have been planted grow. These plants include: Roses, Dogwood, Ocean Spray, Coffee Berry, Ceanothus, and Currants. Canopy cover was not impacted in the short term by our project, however many small seedlings and saplings of invasive canopy species were removed and saplings of native canopy species were planted. Therefore in time, the efforts of this project will result in increased native canopy cover. There are a lot of invasive trees still present in the Hopkins canopy. We hope that funding will be found, perhaps from City of Palo Alto s new Urban Forest Master Plan implementation budget, or elsewhere to inventory and begin to remove these trees to assure the protection of the riparian ecosystem of San Francisquito Creek. 8