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APPENDIX I - BIOLOGICAL RESOURCES Seasonal Wetlands Vernal Pools Eight distinct vernal pools occur in the eastern half of the site. Identification of many plant species within the pool depression areas in fall 1991 was restricted because the flowering season had passed and cattle had heavily grazed most of the vernal pools. Three vernal pool plant species from these sites have been reported,but none of the plants are listed on the California Native Plant Society's list of endangered and threatened species (Muick, 1989). Without the advantage of studying these habitats during their aquatic stage, it is also impossible to say whether species such as the vernal pool fairy shrimp (Branchinecta lynchi), presently under consideration for federal protective listing, are present. Seasonal Wetlands Seasonal wetlands, represented by the Tracy Lakes, occupy approximately 40 percent of the project site. These lakes are the terminal drainage sink for Jahant Slough, and together both the north and south segments drain approximately 17.5 square miles (Kjeldsen-Sinnock& Associates, 1990). The 1939 USGS Lodi Quadrangle map depicts the Tracy Lakes complex with the hatched seasonal wetland shading symbol. The lakes would fill during winter runoff periods and were drained into the Mokelumne River in April or May in order to plant a summer crop such as sudan grass. The grass is harvested before the onset of the following year's rainy season (Brovelli, 1991). Like all seasonal wetlands, these "lakes" vary greatly over any given decade as to the amount of water impounded in a given year. For the past five years of drought conditions in Central California, impoundments of water have been minimal (Lee, 1991). However,during the exceptional 1985-1986 rainy season,the lakes were filled to a capacity equal to that of the Mokelumne River. For the past several years the basins of the Tracy Lakes have not been farmed. However,they have been occasionally disked, and this has laid bare the soil for colonization by aggressive pioneer weed species such as curley dock(Rumex crispus), horseweed(Conyza canadensis)and cocklebur(Xanthiumsp.). The latter species is an extremely successful colonizer of open moist soil and shoreline areas during drought years when such seasonal wetland sites dry early in the spring. During the November 1991 site survey, dense cocklebur stands were found throughout the lake basins and were broken only where a tractor had disked random wide swaths through the weed complex. Permanent Wetlands Two permanent wetland habitats, the permanent pond and the Mokelumne River, are situated on the southern edge of the project site (Figure 4.7-1). The pond was formed by damming an arm of South Tracy Lakes and is maintained by waste irrigation water from adjacent vineyards(Figure 4.7-7). It holds water throughoutthe year,even during extended drought periods. This statement is supported by several of the larger fish specimens netted in the fall 1991 lake survey, and which presumably have lived in the 9