Vernal pools, also called vernal ponds or ephemeral pools, are seasonal pools of water that provide habitat for distinctive plants and animals. They are considered to be a distinctive type of wetland usually devoid of fish, and thus allow the safe development of natal amphibian and insect species unable to withstand competition or predation by fish. Certain tropical fish lineages (such as killifishes) have however adapted to this habitat specifically.
Vernal pools are one of the many plant communities in California and are seasonal pools, as previously mentioned. Vernal pools, however, can be surrounded by many communities/species including grassland, lodgepole pine forest, blue oak woodland, sagebrush steppe, succulent coastal scrub and prairie. These pools are characteristic of Mediterranean climates and are distributed throughout California.
During most years, a vernal pool basin will experience inundation from rain/percipitation, followed by desiccation from evapotranspiration. These conditions are commonly associated with Mediterranean climate. Most pools are dry for at least part of the year, and fill with the winter rains. Some pools may remain at least partially filled with water over the course of a year or more, but all vernal pools dry up periodically. Typically, though, a vernal pool has three phases each year: it is inundated in the Winter (Inundated Phase), it dries slowly in the Spring (Flowering Phase), and in the summer it completely dries (Dry phase). A key time during vernal pool development between the flooding and evaporation phases is the flowering of native species, which attracts pollinators and influences seed distribution patterns. Vernal pools favor native species because non-natives can't handle the conditions of the water staying on the landscape for as long as it does, but not long enough to support truly aquatic species.
A key formation of the vernal pools is due to the claypan, aka hardpan, aquitard, or otherwise impermeable layer. Clay soils bind closely together and become impermeable to water. When it rains the water percolates until it reaches the claypan and sits there, filling up with material and water.
Some authorities restrict the definition of vernal pools to exclude seasonal wetlands that have defined inlet and outlet channels. The justification is that such seasonal wetlands tend to be qualitatively different from isolated vernal pools; this is because they are fed by larger drainage basins so that firstly, inflow contributes higher concentrations of dissolved minerals. Secondly, flow patterns increase the periodic scouring and silting effect of flows through or simply into the wetland. Thirdly, longer distance inflow and outflow make for less strictly endemic populations and plants. Low dissolved mineral concentrations of smaller vernal pool basins may be characterized as oligotrophic, and poorly buffered with rapid pH shifts due to carbon dioxide uptake during photosynthesis.
Vernal pools are so called because they are often, though not necessarily, at their maximum depth in the spring ("vernal" meaning of, relating to, or occurring in the spring). There are many local names for such pools, depending upon the part of the world in which they occur. Vernal pools may form in forests, but they are more typically associated with grasslands and rocky plains or basins. While many vernal pools are only a few meters in width, playas and prairie potholes are usually much larger, but still are otherwise similar in many respects, with high water in wet periods, followed by dry conditions. Some exclude desert playas from the definition of vernal pools because their larger closed drainage basins in areas with high evaporation rates produce higher concentrations of dissolved minerals, with salinity and alkalinity favoring different species. Playas may be inundated less frequently than vernal pools, and inundation typically coincides with colder weather unfavorable for plant growth.
Despite being dry at times, vernal pools teem with life when filled. The most obvious inhabitants are various species of breeding frogs and toads. Some salamanders also utilize vernal pools for reproduction, but the adults may visit the pool only briefly. Other notable inhabitants are Daphnia and fairy shrimp, the latter often used as an indicator species to decisively define a vernal pool. Other indicator species, at least in New England, are the wood frog, the spadefoot toad, and some species of mole salamanders. Certain plant species are also associated with vernal pools, although the particular species depend upon the ecological region. The flora of South African vernal pools, for example, are different from those of Californian vernal pools, and they have characteristic Anostraca, such as various Branchipodopsis species. In some northern areas, tadpole shrimp are more common.
Vernal pools harbor a distinct assemblage of flora and fauna that, in some cases, aren't found anywhere else on the planet. Despite this fact, about 90% of vernal pool ecosystems in California have been destroyed. Disturbingly, much of this destruction has occurred in recent years, with about 13% of remaining vernal pools being lost in the short interval from 1995-2005. The major threats to vernal pool habitats in the Central Valley are agriculture, urbanization, changes in hydrology, climate change, and improperly managed grazing by livestock.
Vernal pools are prime habitats to be targeted for restoration work due to their value as hotpots of biodiversity as well as recent history of extensive destruction and degradation. However, there have been varying rates of success attributed to various restoration efforts. A number of hypotheses exists as to why:
Hypothesis 1: Constructed pools are too deep.
Hypothesis 2: Edges of constructed pools narrower than natural ones.
Hypothesis 3: Constructed pools have steeper slopes than natural ones.
Results: Research suggest that the last two details (Hypothesis 2 & 3) are crucial in determining the habitat value of man-made vernal pools. In general, most constructed pools were too steep and did not have wide enough edges.
There has been a fair amount of controversy surrounding the practice of mitigation, which is the destruction of protected or endangered species and habitats, such as vernal pools, on the condition that whatever entity (business, land manager, etc.) is destroying the habitat will undertake the construction of a replacement habitat to "mitigate" their impacts. This concept is difficult to apply to vernal pools, which represent a tremendous habitat value- but are difficult to successfully replicate using construction methods (as mentioned above). Thus, it has been very controversial to apply mitigation strategies to vernal pool systems due to the obvious risks inherent in trying to reconstruct this kind of habitat. Although, some agencies are now requiring two replacements for every vernal pool that is destroyed, in order to compensate for the low quality of man-made habitat.
Vernal pools can form anywhere that a depression fills with water. They can be found on bedrock of many kinds, or in grasslands that form over a variety of soil types containing silts and clays. They can develop hydric soils which are typical of flooded areas, including accumulations of organic matter, but this may not happen in drier areas. In some cases there is a hard pan layer which causes the retention of water in the pools. The hardpan clay basin accumulates water due to the small particle size and therefore reduced porosity. This permits flooding and development of vernal pools.
In vernal pools, flowering occurs simultaneously because of the seasonality of favorable conditions. Vernal pool ecosystems may include both cosmopolitan species and endemic species adapted to unique environmental conditions. These include moisture gradients, salinity gradients, and reduced levels of competition. Mircrotopographical gradients also contribute to species distribution in vernal pool communities, where plants that flower sooner in the season are more likely to be found at slightly higher elevations than later flowering species. Many vernal pool plants have buried seeds which accumulate in the soil. Different species are suited to different moisture levels, and as water evaporates from the edges of a pool, distinctive zonation of species can be seen.
Many upland perennial plants are unable to withstand the duration of vernal pool inundation; while many wetland plants are unable to withstand desiccation. Wetland plants may also be nutrient limited within small drainage basins. When dissolved carbon dioxide is depleted by daytime photosynthesis, vernal pool species like Howell's quillwort (Isoetes howellii) and pygmyweed (Crassula aquatica) collect carbon dioxide nocturnally using Crassulacean acid metabolism. Vernal pool basin habitats favor annual plants with some uniquely adapted perennials which suffer extensive mortality resembling annual reproduction. Annuals comprise approximately 80 percent of vernal pool flora. Listed below are some genera of the approximately one hundred vascular plant species associated with California vernal pool habitats; although a typical pool will include only 15 to 25 species.
Vernal pools are often threatened by development in the same way that other wetlands are. As a result, most pools have been converted into residential zones, roads, and industrial parks. That is why most extant pools occur on protected or private land such as national parks, and ranches.
A large number of rare, endangered species, and endemic species occur in vernal pool areas. For example, the San Diego mesa mint, a highly endangered plant, is found exclusively in vernal pools in the San Diego area. Another example is the wildflower Lasthenia conjugens, which is found in limited parts of the San Francisco Bay Area. A third example is the herb Limnanthes vinculans endemic to Sonoma County, California.
Many of the amphibians that breed only in vernal pools spend most of their lives in the uplands within hundreds of feet of the vernal pool. Eggs are laid in the vernal pool, then the juveniles leave the pool two or three months later, not to return until the following spring to breed. Therefore, the upland areas surrounding a vernal pool are critical for the survival of these species. In New York state, the endangered tiger salamander (Ambystoma tigrinum) is dependent on vernal pools to breed as described above. A few other obligate vernal pool species are the marbled salamander (Ambystoma opacum), Jefferson's salamander (Ambystoma jeffersonianum), the blue-spotted salamander (Ambystoma laterale) and the spotted salamander (Ambystoma maculatum).
Some other species, notably Anostraca, fairy shrimp and their relatives, lay eggs capable of entering a state of cryptobiosis. They hatch when rains replenish the water of the pool, and no stage of the animals' life cycle leaves the pool, except when eggs are accidentally transported by animal phoresis, wind, or rarely, by flood. Such animal populations may be very old indeed, when the conditions for seasonal vernal waters are stable enough. As an extreme example, Branchipodopsis relictus on the main island of the Socotra archipelago, which is exceedingly remote for what it is, a continental fragment of Gondwana, is believed to have been isolated since the Miocene. Branchipodopsis relictus is correspondingly isolated genetically as well as geographically.
Blennosperma bakeri is a rare species of flowering plant in the daisy family known by the common names Baker's stickyseed and Sonoma sunshine. It is endemic to Sonoma County, California, where it is known from a few remaining vernal pool sites on the wet grasslands of the Laguna de Santa Rosa and Sonoma Valley. It is a federally listed endangered species. It is found alongside other rare vernal pool plants including the Sebastopol meadowfoam, Limnanthes vinculans, and Burke's goldfields, Lasthenia burkei. Threats to its survival include the alteration of its habitat for development, road maintenance, grazing, and agriculture, as well as collecting, herbivory by thrips, and invasive plants.This is a small annual herb under 30 centimeters tall. The leaves are 5 to 15 centimeters long and linear in shape with lobes near the ends. The inflorescence bears a few flower heads. Each head contains a center of yellow disc florets, some of which bear prominent white stigmas and white pollen. Around the edge of the head is a fringe of yellow ray florets with red stigmas. The fruit is an achene a few millimeters long which becomes sticky when wet.
The plant is known from fifteen occurrences, but six of these may be degraded or destroyed. Several artificial vernal pools have been created to increase the numbers of the plant, but the United States Fish and Wildlife Service does not consider these an adequate replacement for natural pools.Boggs Lake Ecological Reserve
The Boggs Lake Ecological Reserve is a nature reserve in Lake County, California. The land area is about one quarter of a square mile and contains a large vernal pool as well as endangered plants such as the Boggs Lake hedge-hyssop.
Boggs Lake is managed by the Nature Conservancy and the California Department of Fish and Game.
It is 8 miles (13 km) south of Clear Lake and has a small parking area and hiking trail loop. The protective fence and interpretive display boards were installed by the Nature Conservancy.
The lake lies in a volcanic depression lined with a very fine covering of volcanic ash a few feet deep that has compacted to become impervious to water. The lake surface covers about 90 acres (360,000 m2) when it is full.Originally a plant preserve of 101 acres (0.41 km2) that resulted from the California Native Plant Society's (CNPS) efforts to save the land from development in 1973, it is today a protected area of sensitive habitat for several endangered plants and animals.Branchinecta lynchi
The vernal pool fairy shrimp, Branchinecta lynchi, is a species of freshwater crustacean in the family Branchinectidae. It is endemic to the U.S. states of Oregon and California, living in vernal pools. They range in size from 0.43 to 0.98 inches (11 to 25 mm) long. Vernal pool fairy shrimp are listed as a vulnerable species on the IUCN Red List, and has been listed as Federally Threatened species since 1994.Branchinecta sandiegonensis
Branchinecta sandiegonensis is a rare species of crustacean in the family Branchinectidae and the order Anostraca, the fairy shrimp. Its common name is San Diego fairy shrimp. It is native to southern California in the United States and Baja California in Mexico. It is a federally listed endangered species of the United States.This fairy shrimp is 8 to 16 millimeters in length.This organism occurs between Santa Barbara, California, and northwestern Baja California, with its distribution centered in San Diego County, California. It lives in vernal pool habitat. It has been identified at 137 vernal pool complexes, many of which have since been extirpated. Others, however, have been restored and preserved, and the shrimp has been reintroduced into appropriate pool habitat.Castilleja campestris
Castilleja campestris is a species of Indian paintbrush known by the common name vernal pool Indian paintbrush. It is native to California and southern Oregon, where it grows in seasonally moist habitat, especially vernal pools.Conservancy fairy shrimp
The conservancy fairy shrimp (Branchinecta conservatio) is a small crustacean in the family Branchinectidae. It ranges in size from about 1.25 centimetres (0.49 in) to 2.5 centimetres (0.98 in) long. Fairy shrimp are aquatic species in the order Anostraca. They have delicate elongate bodies, large stalked compound eyes, no carapaces, and eleven pairs of swimming legs. They glide gracefully upside down, swimming by beating their legs in a complex, wavelike movement that passes from front to back. Fairy shrimp feed on algae, bacteria, protozoa, rotifers and detritus. This species is endemic to California in the United States, primarily Scottsdale Pond in Novato.Lasthenia conjugens
Lasthenia conjugens, commonly known as Contra Costa goldfields, is an endangered species of wildflower endemic to a limited range within the San Francisco Bay Area of the state of California, USA. Specifically this rare species occurs in Napa, Santa Barbara, Solano, Contra Costa, Santa Clara, Monterey and Alameda Counties. This annual herb typically flowers from March through June, and its colonies grow in vernal pool habitats at elevations not exceeding 100 meters above sea level. The Jepson Manual notes that the present distribution is limited to the deltaic Sacramento Valley, principally Napa and Solano Counties, but the historic range of L. conjugens is known to be significantly wider. In any case, historically the range has included parts of the North Coast, Sacramento Valley, and San Francisco Bay Area as well as the South Coast. Alternatively and less frequently this taxon has been referred to as Baeria fremontii var. conjugens.
Even though this plant is found almost exclusively in vernal pools, its behavior in controlled experiments indicates it prefers less than complete inundation. This implies that the plant actually prefers a theoretically drier environment, but is merely less successful than its competitors in surviving in drier (non-inundation) climate regimes.Lepidurus packardi
Lepidurus packardi, known by the common name vernal pool tadpole shrimp, is a rare species of tadpole shrimp (Notostraca).Linderiella occidentalis
Linderiella occidentalis (the California fairy shrimp or California Linderella) is a species of fairy shrimp native to California. It is a small (about 1 cm long) crustacean in the family Chirocephalidae family. It has a delicate elongated body, large stalked compound eyes, no carapace, and eleven pairs of swimming legs. It glides gracefully upside down, swimming by beating its legs in a complex, wavelike movement that passes from front to back. Like other fairy shrimp, L. occidentalis feeds on algae, bacteria, protozoa, rotifers and detritus.
Most fairy shrimp found in California belong to the family Branchinectidae. These include the threatened vernal pool fairy shrimp, which is often found in the same pools. California fairy shrimp are smaller than Branchinecta and have distinctive red eyes.Loch Lomond Vernal Pool Ecological Reserve
The Loch Lomond Vernal Pool Ecological Reserve is a nature reserve of 8.22 acres (33,300 m2) in the community of Loch Lomond in Lake County, California. It is one of 119 ecological reserves managed by the California Department of Fish and Game (CDFG). The ecological reserve system was authorized by the state legislature in 1968 for the purpose of conservation and protection of rare plants, animals and habitats.
The vernal pool provides habitat for the rare and endangered Loch Lomond button celery (Eryngium constancei) (also called coyote-thistle and Constance's coyote-thistle). The button celery was first collected in the vernal pool in 1941, and not until the late 1990s was there another discovery at two other locations in Lake County and one location in Sonoma County.The southern portion of Lake County is in the Mayacamas Mountains of the California Coast Ranges.
Nearby Cobb Mountain (4,722 ft) is the highest peak. Although extensively logged in the past, this area still has Ponderosa pine, sugar pine, and Douglas fir, as well as black oak, with an underbrush of manzanita, ground rose, coffeeberry, and California lilac.Midvalley fairy shrimp
The midvalley fairy shrimp, Branchinecta mesovallensis, is a small (7–20 millimeters or 0.28–0.79 inches) freshwater crustacean in the Branchinectidae family endemic to shallow ephemeral pools (pools that seasonally fill and dry up) near the middle of California's Central Valley. These vernal pool ecosystems are home to other unique organisms adapted to the ephemeral nature of the water cycle in the pools in California's mediterranean climate.
It is one of eight known branchiopod species found only in Northern California. The species swims through the water on its back, using two stalked compound eyes to see where it is going. It propels itself along by beating its phyllopods. These are legs with leaflike or paddlelike structures. The moving phyllopods also serve as gills, extracting oxygen from the water stream they create. This places the shrimp in the Class Branchiopoda ("branchio" meaning gill, and "poda" meaning feet).Myosurus
The genus Myosurus, or mousetail, belongs to the buttercup family (Ranunculaceae). It comprises about 15 species of annual scapose herbs. These herbs are nearly cosmopolitan (lacking in eastern Asia and tropical regions), with a center of diversity in western North America. The flowers are easily recognised by bearing 6 stamens with numerous ovaries on a stalk (accounting for the name "mousetail").
Myosurus apetalus - bristly mousetail
Myosurus cupulatus - Arizona mousetail
Myosurus minimus - tiny mousetail
Myosurus nitidus - western mousetail
Myosurus sessilis - vernal pool mousetailMyosurus sessilis
Myosurus sessilis is a species of flowering plant in the buttercup family known by the common name vernal pool mousetail. It is native to southern Oregon and the Central Valley of California, where it grows in vernal pools and other wet grassland habitat. It is an annual plant forming a small tuft up to about 10 centimeters tall. The leaves are narrow and linear in shape, measuring up to 7 centimeters in length. The inflorescence produces a single flower which has an elongated, cylindrical or cone-shaped receptacle up to 3 centimeters long. At the base of the receptacle are curving, spurred sepals and three to five tiny petals.Navarretia
Navarretia is a genus of about 30 species of flowering plants related to the phloxes and the gilias. This is one genus of plants, among others, which are sometimes called pincushionplants. The inflorescence which bears the flowers is surrounded by frilly green bracts bearing soft spines, giving it the appearance of a pincushion. Several species are members of the vernal pool ecosystem.
Navarretia atractyloides - hollyleaf pincushionplant
Navarretia breweri - Brewer's pincushionplant
Navarretia capillaris - miniature gilia
Navarretia cotulifolia - cotulaleaf pincushionplant
Navarretia divaricata - divaricate navarretia
Navarretia eriocephala - hoary pincushionplant
Navarretia filicaulis - threadstem pincushionplant
Navarretia fossalis - vernal pool pincushionplant
Navarretia hamata - hooked pincushionplant
Navarretia heterandra - Tehama pincushionplant
Navarretia heterodoxa - Calistoga pincushionplant
Navarretia intertexta - needleleaf pincushionplant
Navarretia jaredii - mitrefruit pincushionplant
Navarretia jepsonii - Jepson's pincushionplant
Navarretia leptalea - Bridges' pincushionplant
Navarretia leucocephala - whitehead pincushionplant, many-flowered pincushionplant
Navarretia mellita - honey-scented pincushionplant
Navarretia nigelliformis - adobe pincushionplant
Navarretia ojaiensis - Ojai navarretia
Navarretia peninsularis - Baja pincushionplant
Navarretia prolifera - bur pincushionplant
Navarretia prostrata - prostrate pincushionplant
Navarretia pubescens - downy pincushionplant
Navarretia rosulata - San Anselmo pincushionplant
Navarretia setiloba - Piute Mountain pincushionplant
Navarretia sinistra - Alva Day's pincushionplant
Navarretia squarrosa - skunkbush
Navarretia subuligera - awl-leaf pincushionplant
Navarretia tagetina - marigold pincushionplant
Navarretia viscidula - sticky pincushionplantNavarretia prostrata
Navarretia prostrata is an uncommon species of flowering plant in the phlox family known by the common names prostrate pincushionplant and prostrate vernal pool navarretia. It is endemic to California.
The plant has a scattered distribution from the San Francisco Bay Area, through the Transverse Ranges and Peninsular Ranges, to the southern border. It is an occasional member of the flora in vernal pools and similar habitat.Pogogyne nudiuscula
Pogogyne nudiuscula is a rare species of flowering plant in the mint family known by the common name Otay mesa mint. It is native to southern San Diego County, California, where it is known only from Otay Mesa near the border with Baja California. It was identified on land south of the Mexican border, but these occurrences have probably been extirpated. It is now known from seven vernal pool complexes just north of the border, and it is a federally listed endangered species of the United States.This annual herb produces an erect stem reaching 30 centimeters in maximum height. Its herbage is strongly aromatic and coated very thinly with stiff hairs, or lacking hairs. The inflorescence is an interrupted series of flower clusters. The flowers are just over a centimeter long, bell-shaped with narrow throats, and bright purple in color, usually with some white on the lower lip.
This plant faces a number of threats related to the loss and destruction of habitat containing its rare vernal pool ecosystem. These threats include urban development, trash dumping and pollution, vehicles, fire, grazing, and alterations in the local hydrology.Pond
A pond is an area filled with water, either natural or artificial, that is smaller than a lake. It may arise naturally in floodplains as part of a river system, or be a somewhat isolated depression (such as a kettle, vernal pool, or prairie pothole). It may contain shallow water with marsh and aquatic plants and animals.Factors impacting the type of life found in a pond include depth and duration of water level, nutrient level, shade, presence or absence of inlets and outlets, effects of grazing animals, and salinity.Ponds are frequently man-made, or expanded beyond their original depth and bounds. Among their many uses, ponds provide water for agriculture and livestock, aid in habitat restoration, serve as fish hatcheries, are components of landscape architecture, may store thermal energy as solar ponds, and treat wastewater as treatment ponds.
Ponds may be fresh, saltwater, or brackish.Sidalcea calycosa
Sidalcea calycosa is a species of flowering plant in the mallow family known by the common names annual checkerbloom, checker mallow, and vernal pool checkerbloom.Tuctoria mucronata
The grass Tuctoria mucronata, which is known by several common names including prickly spiralgrass, Solano grass, and Crampton's tuctoria, is a federally listed endangered plant species endemic to two counties in northern California. It is a small annual, with stems growing decumbent against the ground to a maximum length of 12 cm, and turning upward at the tips. The leaves are 2–4 cm long, and secrete a sticky, aromatic juice. In the spring, the grass bears a small inflorescence 1.5–6 cm long, with numerous crowded spikelets.
Solano grass is a vernal pool plant. It is only found in these seasonally wet areas, a type of habitat which is endangered. This species is thought to have once grown in isolated parts the northern Sacramento-San Joaquin Delta, in areas which flooded during the wet season, but any former habitat there has been long since reclaimed for agriculture. Only a few individuals of the plant now exist, mostly in Yolo County. It was found during the 1990s at Jepson Prairie Preserve, an area dedicated to conserving vernal pool habitat, but it may no longer exist there.
Loss of critical habitat is the main cause of the near extinction of Solano grass. This loss is caused by land reclamation for development, recreation, and agricultural use, including for grazing animals, fertilizer runoff, and disturbance of the natural hydrology of the Central Valley. Invasive plants have also played a role in crowding out more delicate native grasses, such as Solano grass, Greene's tuctoria (Tuctoria greenei), Colusa grass (Neostapfia colusana), and several species of genus Orcuttia.