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7 S BIOTICS INTRODUCTION This supplemental biotic study was completed in response to the numerous comments received on the Buckeye Ranch Draft EIR. At the time the EIR was prepared, many of the plant and wildlife studies could not be undertaken due to scheduling of the document. Additional surveys were then conducted during the late winter, spring and early summer months of 1992. This survey, coupled with the earlier effort, forms the basis of the impact analysis. Surveys were conducted over a 10-month period from mid-October 1991 to late August 1992. The latter survey spanned the time segment in Central California during which most major biotic events take place. This, coupled with the fact that the 1991-92 winter was the first in six years to produce a near normal rainfall after a severe drought cycle,created a set of environmental conditions which permitted the most complete biological evaluation of this area to date. Once the plant and wildlife value of the site could be determined, a more thorough analysis of the applicant's plan could be made. ENVIRONMENTAL SETTING Permanent Wetlands Tracy Lakes The most dominant biological feature of this area are the Tracy Lakes which occupy approximately 40 percent of the project site (Figure 4.7-1). These 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 lakes fill during winters of average or above average runoff periods. Like all seasonal wetlands, these "lakes" vary greatly over time as to the amount of water impounded on 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 1985-86 winter they were filled to a capacity equal to that of the adjacent Mokelumne River during that high rainfall season (Brovelli, 1991). From approximately 1940 to the mid-1980s the basins of the Tracy Lakes were farmed during the summer and early fall months by the Brovelli family. This was accomplished by draining the winter impoundment of water into the Mokelumne River in late spring and then discing and planting the fertile lake floors. For several years prior to this study the basins of the Tracy Lakes have not been farmed. However, they have been occasionally disced, and this has laid bare the soil for colonization by aggressive pioneer weed species such as horseweed(Conyza canadensis)and cocklebur(Xanthium sp.). The latter species is an extremely successful colonizer of open moist soil and shoreline areas during drought years when such seasonal wetland sites dry in the early spring. At the beginning of the study for the DEIR in fall 1991,dense cocklebur stands were found throughout the lake basins and broken only where a tractor had disced random wide swaths through the weed complex. The return of a near normal rainfall pattern in Central California during the 1991-92 winter resulted in water impoundment in the lake basins by late December. By mid-January they were filled to near capacity(Figure 4.7-2). Measurements taken by the EIR biologist found depths at the lake centers ranged 1