The serpentine grasslands at Edgewood are widely recognized as the outstanding feature of the Park and Preserve. Unfortunately, all is not well in the serpentine grassland. The flagship animal species, the Bay checkerspot butterfly, has rapidly declined from several thousand individuals in 1997 to near extinction as of Spring 2002. Qualitative observations pinpointed a major change in the habitat: an extensive non-native grass invasion, primarily by Italian ryegrass (Lolium multiflorum), had eliminated many acres of Dwarf plantain (Plantago erecta), the primary food plant of the butterfly. The grass invasion was enhanced by record El NiÃ±o rains in 1997 and 1998.
In Fall 2000, San Mateo County obtained a $70,000 grant from the National Fish and Wildlife Foundation (NFWF) to inventory current conditions, and to begin restoration experiments. The grant is being administered through the San Mateo County Parks Foundation.
The inventory had two components: plant cover transects with several hundred quarter-square meter quadrats in which all species were recorded, and aerial photography. The plant quadrats showed that Lolium multiflorum was the single most abundant species in the main 33 acre block of serpentine, with about 30% cover. Plantago was third with about 6%. The distribution of Lolium and Plantago were negatively correlated, and showed 3 interrelated patterns: 1) Lolium was most abundant on deeper soils, 2) Lolium was more abundant east of I-280 than west, and 3) East of the freeway, Lolium was more abundant closer to the freeway. Only about 20% of the serpentine grassland had sufficient Plantago to support the butterfly, and much of that tended to be on the shallowest soils (10-20 cm), where plants dry rapidly in the spring. The best remaining habitat was greater than 300-400 meters from the freeway.
Similar, but more intense grass invasions have been noted in the South Bay, where high levels of smog act as slow-release nitrogen fertilizer through a process called â€œdry deposition.â€ Various reactive nitrogen compounds in smog are absorbed by plants and soil surfaces. The observations at Edgewood indicate that the nitrogen oxides produced by 100,000 cars/day passing on the freeway are providing sufficient nitrogen inputs through dry deposition to effectively fertilize the grassland and allow for nitrogen-loving grasses to invade otherwise resistant serpentine soils.
Aerial photographs, were extremely useful in mapping the extent of grass invasion across the entire serpentine grassland habitat. Areas of high grass cover showed up strongly, and it was possible to classify the photograph into habitat classes corresponding to grass-dominated, forb-dominated, and largely bare rock and soil.
Several blocks of transects were set up to accommodate restoration experiments. Planned treatments included mowing, goat grazing, and prescribed fire.
The mowing experiment was executed in May 2001, and preliminary results are encouraging. Mowing reduced Lolium cover from about 50% to 15% on average, and increased Plantago cover from 3% to 9%. Individual Plantago plants were much larger and healthier than those growing in control areas, and occupied areas of deeper soils. Overall species diversity in the mow plots increased from ~8 species per quadrat to ~11 species.
In March 2002, a herd of 48 goats was brought on site for 6 days. Four small plots were thoroughly grazed to the ground, and another plot was grazed at half intensity. The results of these experiments will not be known in full until Spring 2003.
Prescribed burns, planned earlier this year, were not executed due to safety concerns.
The butterfly population is at or near extinction in 2002. A comprehensive look at reintroduction options, using individuals from healthy South Bay populations, will be part of the final report in Fall 2002
The project has generated a lot of positive excitement among the Edgewood community, the US Fish and Wildlife Service, and local conservationists and scientists. The park staff at all levels have been enthusiastic participants, and further funding for continued experiments and larger-scale restoration is being pursued.