QUANTITATIVE ANALYSIS OF VEGETATION AT THE RICHVALE VERNAL POOLS, CALIFORNIA

California vernal pools exhibit vegetation of mainly native, annual vascular plants that flower and set seed as standing water from the Mediterranean climate wet season evaporates. Deeper depressions often show concentric rings of color from the different species responding to progressive drying of the habitat. Vernal pool plant life was numerically analyzed in 1979 near Richvale, in the Sacramento Valley, by sampling in a regular grid pattern that covered both the pool and the adjacent annual grassland. Each species was measured once in all sample sites, all data were pooled and an importance value was determined for each of the 61 species. Species are discussed in relation to the high water line of a pool (maximum extent of standing water). Samples covering all regions of a plot showed there are “pool species” (e.g., Lasthenia fremontii ) with nearly identical distributions almost totally within high water line. Four native species made up 75% of all the plants counted in the pool samples. In general, pool species had higher densities inside the high water line than the “non‐pool species” had outside the high‐water line. Non‐pool species (e.g., Aira caryophyllea ) tended to occur in the pool samples more than the pool species occurred outside the pool. Some species (e.g., Limnanthes alba ) had roughly similar absolute and importance values for pool and non‐pool areas; these were called “transition species,” and had less importance than either pool or non‐pool species throughout the plots. The two study plots, 40 m apart, had similar rankings for the top pool, non‐pool and transition species: importance of the species varied within each of these two neighboring pools.