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

Download date 26/09/2021 20:28:15

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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 dominated 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, grassgenera 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. Federal Register litter) largely produc- 57(90): 19857-19862. tivity and seasonal species composi- Conclusion Gifford, G.F. and R.H. Hawkins. 1978. tion of California's annual grasslands. Hydrologic impacts of grazingon infiltration: of residue is the A critical review. Water Resources Management plant After factors Research. 1 3. factor that can be most con- considering ecological 4(2):305-31 readily governingvernal pools and California's Hanes,W.T., B. Hecht,and L.P. Stromberg. 1990. Water of vernal in trolled by a rangeland manager. Low annual rangeland, as well field obser- relationships pools amounts of residue in fall favors the the Sacramento region, California. In: D.H. vations, a case may be made for the Ikeda and R.A. Schlising (eds.), Vernal pool growth of a diversity of plants including benefits of livestock grazing vernal plants- their habitat and biology, 40-60. low-stature, spring-maturing forbs, habitats on California's annual Studies from the Herbarium No. 8, pool California State Chico. such as filaree (Erodium ssp.) and Native vernal University, grasslands. pool plants Heady, H.F. 1977. Valley grassland. In: M.G. summer annuals, such as turkey and fauna have co-existed in these Barbour and J. Major eds. Terrestrial mullein (Eremocarpus setigerus). In grazed ecosystemsfor at least the past Vegetation of California. New York: John and Sons. 1,002 the absence of livestock, plant residue century. The extent to which grazing Wiley pp. can accumulate and annual Holland, A. F. 1978. The Geographic and grassland animals impacted vernal pool ecosys- Edaphic Distribution of Vernal Pools in the habitats are often dominated by tall tems before the arrival of Spaniards in Great Central Valley, California. California dense stands of grasses such as California is however with Native Plant SocietySpec. PubI. No. 4. debatable, R. and K. Jam. Vernal brome (Bromus the arrival of the Holland, F., S. 1984. ripgut diandrus), Spaniards grasslands pools. In: M. G. Barbour and J. Major medusahead (Taeniatherumca put- surrounding the vernal pools in the (Eds.), Terrestrial Vegetation of California. medusae), or wild oats (Avina fatua). Sacramento Valley significantly JohnWiley and Sons,New York. Medusahead is one the dominate Liacos, L..G. 1962. Water yields as influ- of changed. It is this "newly" evolved of in the annual enced by degrees grazing grasses surrounding many ver- grassland, full of exotic aggressive Californiawinter grasslands. J. Range nal pools in the SacramentoValley. annuals, that must be managed if Manage. 15:34-42. Once medusahead becomes estab- California's endemic flora and fauna Menke,J.W. 1992. Grazing and fire management native in dense form- are to be conserved. for perennial grass restoration lished, it grows stands, species in California grasslands. Fremontia ing a mat of stems 2 to 5 inches thick. Management of California's annual 20(2):22-25. Evidence indicates the dense litter grasslands with vernal pool habitat Stone, R.D. G.L. Clifton, W.B. DaVilla, J.C. D.W. 1987. cover is important in the competitive should not only prevent exotic species Stebbins, Taylor. EndangermentStatus of the Grass Tribe relationship because other plants fail from invading vernal pools, but also Orcuttieae and Chamasyce hooveri to grow under litter cover (Evans and should not compromise the hydrology (Euphorbiaceae) In: the Central Valley of Young 1970). Field observations in that creates vernal pools. Excluding California. In: Elias, T.S., ed. Conservation and Management of Rare and Endangered and around ungrazed pools in the livestock grazing from vernal pool Plants. Proceeding of a California Sacramento Valley indicate that a habitats without an alternative proven Conference on the Conservation and dense thatch of medusa head can method to manage the surrounding Management of Rare and Endangered the A Plants. The California Native Plant Society. develop right to pool's edge. grasslands could (and has) resulted in 1987:239-247. managed livestock grazing program a decline in biological diversity. Zedler, P. H. 1987. The ecology of southern can control medusahead and reduce California vernal pools:a community profile. the thatch it creates. This allows for a U.S. Fish WildI. Serv. Biol. Rep. 85(7.11) 136 pp. greater diversity of rangeland plants References wildflowers found including commonly Bauder, E. T. 1987. Threats to San Diego around the edges of vernal pools. Vernal Pools and a Case Study in Altered Similarly, managed grazing can sus- Pool Hydrology. In: Elias, T.S., ed. tain vernal pool habitat for stands of Conservation and Management of Rare Orcuttia and and Endangered Plants. Proceedingof a Neostaphia, endangered California Conference on the Conservation vernal pool plants. Crampton (1959) and Management of Rare and Endangered found that "the best stands of either Orcuttia Plants. The California Native Plant Society. or occur in the absence 1987:209-213 Neostapha mostly Blackburn, W. H. 1975. Factors of ..The of the influencing other vegetation. presence infiltration and sediment production of semi-