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Biology field trip to study vernal pools

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The Great Valley of California has a Mediterranean climate, one of only five such areas on earth. It is characterized by hot dry summers and wet, cool winters. There are six to eight inches of rain in the southern valley and 20 inches in the north. Vernal pool plants and creatures have established strategies to grow in these conditions. They must grow fast in the spring, reproduce, and leave their seeds in the ground. They have survival strategies as well: migrate, aestivate (summer dormancy) and have an over summering propagule. This is a method to come to life when the conditions are right by having seeds, spores or cysts. This applies to non-plant creatures also which leave eggs or pupae in the soil.

There are five Great Valley ecosystems:

  1. Great Valley grasslands, which include vernal pools. There are trees along rivers in percolated soils. The grassland here now is not native but introduced species.
  2. Freshwater marsh, which is highly productive. This has been 90% wiped out in California.
  3. Great Valley riparian forests, which has water throughout the summer due to runoff. Their two to five mile-wide floodplain attest to the flooding possible.
  4. Great Valley oak savanna. Oaks can photosynthesize at high temperatures , but they are being wiped out by grazing and farming.
  5. Alkali sink scrub, which occurs in low flat playas like the Tulare basin, a desert-like habitat.

Vernal (spring) pools are a Mediterranean climate intermittent pool which are dry for nine months of the year. They are mostly in California, but occur also in Baja and South Africa. They are a tiny little ecosystem with no transition in or out. It is a discrete aquatic ephemeral ecosystem, containing food and what eats the food. Occasionally birds bring things into the pool. These pools form because something below the pool keeps the water in them, e.g., clay pan, bedrock or a volcanic layer. This solid keeps water from percolating through the ground and only evaporation gets rid of the water.

There are three types of pools: 1) valley pools, both fresh and alkali, 2) Sierran terrace, and 3) volcanic table land. What changes in a pool over the year is the volume of water, the temperature of the water, the turbidity of the water, the oxygen concentration, the food availability, crowding and the periods of inundation. Vernal pools are hotbeds of evolution. They are filled with endemic (narrowly restricted) species. There are lots of things that can't live here. Different species can tolerate different periods of inundation. Plants and algae have to get to the pool first. Then seed shrimp eat the algae. The hatching time of the seed and clam shrimp is important so that they have food to eat when they hatch. The vernal pool biota also includes cyanobacteria, protozoa, planaria, crustaceans, spiders, insects and amphibians.

The Trip:

The table around the Sierra College campus is a volcanic lahar and can contain lava cap type vernal pools. This lahar formed as warm muds from volcanic activity in the Miocene flowed down the winding river beds here at that time. This same scenario stretches form Oroville to Fresno. The flanks of the lahar has trees because water can run through the fractured soil found there. We see Johnny Tucks, Orthocarpus erianthus, in bloom.

We drive up Highway 65 and have an area where there are Sierran terrace pools. The pools are here because of the clays washed down from higher up. Lincoln has very fine Eocene clays. We see several non-native plants such as palm trees and wild radish. A yellow billed magpie is seen, a member of the crow family. (There are crows in the valley, but few ravens.) Eucalyptus, imported from Australia, is along the road.

Near Oroville and the Feather River we see bush lupines. At a stop off Table Mountain Blvd., we walk to identify the plants. There are blue oaks with their ashy gray bark; interim live oaks; Brodiaea; buttercups; foothill pines; virgin's bower, Clematis ligustifoia (pale yellow flowers); poison oak; Pholistoma (white flowers; and miner's lettuce, Claytonia (montia) perfoliata. We also see a pipe vine swallow tail butterfly and a rufus-sided tohee. Lupines have a small purple flower and are a member of the pea family. There are over 100 species in California.

Live oaks, Quercus wislizenii, holds old leaves year round and now has new leaves also. Blue oaks, Q. douglasii, has glossy green leaves with deep lobes. It is dimorphic (2 or more shapes to leaves). The male flowers are dangling catkins and the female flowers are tiny.

Up on Table Mountain we see lots of yellow goldfield, Lasthenia californica. This is the Mehrton Formation with very shallow soils. There are trees of the flanks where water comes out. We see turkey vultures and a horned lark. (The flowers seen are noted on the Table Mountain Flora list.)

We leave and drive to Chico and Bidwell Park. There is an old oak with acorns embedded in holes made by acorn woodpeckers. We see Dutchman's Pipe, Aristolocica californica, its fruit is the only place pine vine swallowtail butterfly lays its eggs on. Down by Big Chico Creek there are native sycamores and foothill pines. Farther down are valley oaks. Also a redbud, Cercius oxydenalis, and a white ash, Almus rhombofolia, live here, as well as Ponderosa pine, incense cedar and manzanita. Mugwort, Artemesia douglasiana, a fibrous sagebrush with fragrant leaves grows here. A wild cucumber vine, manroot, Marah sp., creates giant tubers.

We move on and see meadow foam, Limnanthacae, in the distance. We stop a Nature Conservancy location where there are vernal pools. One pool is large with cemented ash bottom. We find tadpole shrimp with eggs, copepods (red crustaceans), fairy shrimp, clam shrimp, backswimmers, boatmen, water fleas, nostoc blue-green algae, red worms, and seed shrimp. The fairy shrimp species here is the only place they exist. This pool was completely dry a few months ago and now is teeming with life. There are northern harrier hawks and killdeer flying nearby. As a vernal pool dries up, the creatures activate their dormant strategies. If there is lots of water and it warms up there are numerous generations. If there is less water and cooler, only one generation hatches. If environmental conditions are poor the eggs may go into a cyst; if good the eggs hatch. Alpha diversity means the diversity within one pool. Beta diversity relates to two pools relative to each other.

Plants around the pools include Brodea hyacyathia, Triteleia hyacinthina, delphiniums, and Medusahead grass.

The last pool really brought home the diversity of life that springs up out of a seemingly dry spot in the ground. Before this trip I had no idea of this unique California asset.

Mike Price, spring 1996

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