Patterns in Time and Space for Rare Macroinvertebrates and Vascular Plants in Vernal Pool Ecosystems at the Vina Plains Preserve, and Implications for Pool Landscape Management

This report combined spring-aquatic observations (starting in March 1995) of select macroinvertebrates, with summer-dry observations (extending through August 1995) of select plants from the same vernal pool ecosystems at the Vina Plains Preserve, southern Tehama County, California. Density indices were developed from catch-and-release collections of Lepidurus packardi and Branchinecta conservatio; L. packardi carapace lengths were also measured. The plants, Chamaesyce hooveri, Orcuttia tenuis, Orcuttia pilosa, and Tuctoria greenei were sampled for frequency and density using quadrats along pool transects. Lepidurus packardi density indices were 20-85 individuals per m2 of pool floor with juveniles and adults, and near 10 individuals per m2 with adults only. Different populations displayed variable time of second generation, maximum carapace size (24-39 mm) and time of adult mortality (April to June). Branchinecta conservatio density index ranged from 3-99 individuals per m3 of water sampled, with four pools having large and three having small populations. Nine of the larger pools contained one to three species of the plants, with Tuctoria alone most of the time. Transect sampling in different pools showed variation (e.g., for Chamaesyce) in frequency (0.006-0.141), density (0.1 to 6 plants/ m2), population size (2,000-183,400) and distribution in individual pools. These features, as well as co-occurring exotic plants, distinguished each pool in this complex as unique. This documented population biodiversity implies that these ecosystems have different environmental conditions that control the break in dormancy and growth. Successful vernal pool species preservation requires long-term monitoring of individual species considering the pattern interface between these populations and vernal pool ecosystems. Population differences of these aquatic macroinvertebrates and summer plants can only be maintained in a series of pools as part of an extensive landscape. This calls for the preservation of landscape units with diverse vernal pool ecosystems. Vina Plains Preserve is an ideal area for preserve expansion. CITATION. Pages 161-168 in: C.W. Witham, E.T. Bauder, D. Belk, W.R. Ferren Jr., and R. Ornduff (Editors). Ecology, Conservation, and Management of Vernal Pool Ecosystems – Proceedings from a 1996 Conference. California Native Plant Society, Sacramento, CA. 1998.