Vernal Pools on California's Annual Grasslands

Vernal Pools on California's Annual Grasslands Item Type text; Article Authors Barry, Sheila Citation Barry, S. (1995). Vernal pools on California's annual grasslands. Rangelands, 17(5), 173-175. Publisher Society for Range Management Journal Rangelands Rights Copyright © Society for Range Management. Download date 26/09/2021 20:28:15 Item License http://rightsstatements.org/vocab/InC/1.0/ Version Final published version Link to Item http://hdl.handle.net/10150/639063 RANGELANDS 17(5), October 1995 173 Vernal Pools on California's Annual Grasslands Sheila Barry The rangelands of the Northern Society estimated that 90% of one of the most significant impacts to Sacramento Valley are comprised of a California's Central Valley vernal pool the vernal pool annual grass popula- great variety of exotic annual plant environments had been eliminated tions. They found that Cocklebur species. These plant species were first (Holland, 1978). Currently, three ver- (Xanthium strumarium), Bindweed introduced in 1769 with the arrival of nal pool plants and four vernal pool (Convolvulus arvensis), etc. in large the Spanish Missions and continued invertebrate species occurring in the vernal pools threatened the habitat of from Gold Rush days to today. By their Sacramento Valley are listed as two endangered vernal pool plant very nature, exotic annual species are threatened or endangered under the species, Hairy Orcutt Grass (Orcuttia aggressive and highly competitive. Federal Endangered Species Act. pilosa) and Hoover's Spurge Because they evolved during thou- Vernal pools and their associated flora (Chamaesyce hooveri). In smaller, sands of years of heavy grazing and and fauna are threatened by a variety swalelike pools they found the intro- periodic drought in their native habitat, of human-caused activities that duced perennial grass, Italian exotic annuals are capable of produc- change the pool's hydrology including Ryegrass (Lolium multiforum), to be a ing some seed under the most adverse grazing disturbances and weather regimes. Consequently, they present a formidable obstacle to re- establishment of native plants (Menke 1992). Exotic annuals now comprise the stable communities of most of California's grasslands (Heady 1977). Despite the invasion of exotic annuals, native plants have thrived on California's grasslands in vernal pools. In fact, Holland and Jam (1984) found that vernal pools are typically dominat- ed by native plants. Vernal pools are seasonally dry depressions which catch and hold water from winter precipitation until it evaporates into the air and/or percolates into the soil in the spring or summer. They are a type of wetland unique to California and a few other places in the world. Vernal pools provide habitat for an unusual diversity of native crustaceans,grasses and Ungrazed Vernal Pool (excluded from livestock grazing for the past 10 years) Vina wildflowers. These islands of native Plains, TehamaCo. April 1993. flora and fauna should continue to exist and thrive among the exotic annuals as they have for the past 100 urban development,water supply/flood problem for the endangered vernal years if they are protected and proper- control activities and conversion of pool plant, Greene's Tuctoria (Tuctoria ly managed. land to agricultural use (Federal greenei). Register 1992). These habitats are The invasion of weedy exotic Threatsto Vernal Pools in the also indirectly affected by modifica- species into vernal pool habitat can Sacramento tions of surrounding uplands that alter actually be interrelated with changes Valley in In 1978 the California Native Plant a vernal pool's watershed. hydrology.The frequency and abun- Beyond changes in vernal pool dance of weedy upland species in vernal tends to increase Universityof california CooperativeExtension, hydrology, the introduction of exotic pools during Farm Advisor, Tehama, Glenn, and Colusa is the threat to vernal drought years (Holland and Jam, species major Native vernal are Counties, P.O. Box 370, Red Bluff Calif. pool habitats. Stone et al. (1987) 1984). pool species 96080,(916) 527-3101 to the seasonal of noted that competition from weeds is adapted pattern 174 RANGELANDS 17(5), October 1995 result of surface runoff. In fact, surface runoff seems to be essential for maintaining an adequate inundation period. Many studies conducted on grasslands in temperate areas of the United States have shown that the amount of runoff is significantly influenced by the amount of vegetation. Runoff decreas- es in proportion to an increase in the amount of vegetation (Blackburn 1975). Vegetation cover retards runoff and generally allows for greater oppor- tunity for water infiltration. Standing dry or dead vegetation may also increase net rain loss due to direct evaporation. Grazing animals may help to maintain the hydrology of the uplands surrounding vernal pools by preventing the excessive accumulation of plant material. Mechanical impact by grazing animals may also be important for main- Grazed VernalPool Vina Tehama Calif. Plains, County, April 1993. taining the vernal pool hydrology by sustaining the soil conditions that cre- ate vernal pool habitat. Gifford and drought and standing water in the perpetuate vernal pool plants. When Hawkins (1978) reviewed literature on pools. If the period of standing water is horses were removed from a heavily the hydrologic impacts of grazing reduced, the invasion of exotic species grazed horse pasture on the University intensities. They concluded that is promoted. As exotic herbs and of California Santa Barbara campus ungrazed rates of infiltration were sta- grasses invade, the period of inunda- the abundance of vernal pool different from rates at tion species tistically grazed may be further reduced. Bauder seemed to decline in proportionto the any intensity. They found no signifi- (1987) demonstrated that the percent- increase in nonpool species. cant difference between light and age of vegetation in a vernal pool The effects of on moderate but a distinct differ- which grazing rangeland grazing, is exotic is closely tied to length resources are most certainly as com- ence between heavy grazing and of inundation. When were light the pools plex as the various ecosystems in or moderate grazing. only inundated for four weeks or less which livestock grazing occurs. It is Liacos (1962) studied the influence during a year, one-third of the species to out of of livestock on water around the usually easy point examples grazing yields pools' margin were exotic. resource degradation caused by over- and bulk density on California's annual With over two months of inundation instances where He found less than 10 grazing; however, grasslands. that sites heavily percent of species around properly managed maintains for more than 35 had the were exotic. grazing grazed years pool ecological balances and/or promotes more dense and more shallow soil biological diversity are probably than ungrazed sites. Water yield was Grazing-A Tool to Preserve Vernal numerous, especially on California's many times greater under heavy graz- Pool Habitats annual grassland. Properly managed ing. Liacos concluded that when heavy Grazing may be used as a tool to grazing in vernal pool habitats on grazing occurred year after year the maintain vernal pool hydrology and California's annual rangeland may be soil forming process was slowed prevent the invasion of exotic weeds. one such instance where ecological down. It would appear that vernal pool Livestock have grazed in and among balances and biological diversity are habitats on annual grasslands can be most vernal pools in the Sacramento enhanced. maintained if current grazing intensi- Valley for at least a century. Although, ties continue. there are no published data on the to Maintain Vernal Pool In addition to maintaining the hydro- effects of on Grazing grazing vernal pools, Hydrology logic aspects of a vernal pool, the some biologist have made mention of Based on limited monitoring and per- trampling of a grazing animal may also grazing impacts on vernal pools. sonal observations of vernal in influencethe of Zedler pools diversity microecosys- (1987) stated that moderate the Sacramento Hanes et al. tems within a vernal When the cattle or horse region pool. grazing does not seem (1990) reported that direct vernal are wet, animal distur- to pose much of a threat to the precipita- pools persis- tion appears to be a dominant input bances can cause tence of vernal pool plants despite the microdepressions. initially filling pools during the winter. These microdepressions may enable "disruptive" effect of trampling. He also Later in the noted season, flucuations in a shallower pools to provide habitat for that grazing may even help to water level be a pool's may largely vernal pool plants and animals gener- RANGELANDS 17(5), October1995 175 ally found in deeper vernal pools. For ubiquitous vernal pool (perennials) coyote arid rangelands in Nevada. Water bella covers the thistle and the Resources Research 11:929-937. example, Downingia (E,yngium vaseyi) sedge, Beecher. 1959. The bottom of Eleochans restricts the of Crampton, grass genera deeper pools, but is also palustns, density Orcuttia and Neostapfia: a study in habitat found in shallower pools when deeper Orcuttiaand Neostapfia." Observations and morphological specialization. Madrono microdepressionsheld water for a pro- across a fenceline that straddles the main 15:97-110. Evans, R.A. and J.A. Young. 1970. Plant lit- longed time. portion of a vernal pool at Rancho Seco in ter and establishment of alien annual weed Sacramentosuggest that a managed graz- species in rangelandcommunities. Weed Grazing to Prevent Invasion of ing regime may help to control Eleochans. Sci. 18:697-703. The of Eleocharison the side ofthe Federal Register. 1992. Endangered and Weedy Species density threatenedwildlife and to which is plants; proposal Four factors (precipitation, tempera- pool heavily grazed is significantly determine endangered status for four fairy ture, soil characteristics, and plant reduced (Stone et all987). shrimp and the vernal pool tadpole shrimp residue or control in California.

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