This setting provides a large-scale "natural" experiment¹ on ecosystem development (succession) in arid environments. We have an opportunity to study the upland ecosystem processes as the lake regresses and transgresses at a rate 100 times or more faster than lake-level changes occurred under natural climate change.  We began study of the vegetation and landforms of the dune systems and exposed playa as the lake rapidly regressed during the 1980's as a result of water diversions and a significant drought, with the lake reaching an historical low level of 6374'. Now we are observing our study plots as the lake level is rising as a result of the recent (1993) water rights decision mandating a lake level of 6400' and a series of wet years, including a significant El Niño. As the lake regressed, it left exposed playa as a surface for plant and animal colonization; we were able to investigate the processes of succession in arid environments. As the lake is currently transgressing, we are able to observe the effects of a rising water table (as fresh water rides on top of the heavy, saline lake water) on upland perennial phreatophytic shrubs.

The Toft study site area in 1930 (photos from the Fairchild collection at Whittier College). Notice the lagoon filled with water as a result of the higher lake level (approximately 6410' at this time). The red box surrounds the sulphur pond, which is a feature that can be used for scale and perspective in these photos and also is the main local landmark giving its name to the USGS quadrangle topo map. This view shows the lake at the bottom of the picture, a reverse view from that above of the dunes from the other side and lake at the top of the piciture. The lake has been confined to the basin delimited by the gravelly beach for at least 100 years and is much the same as Israel Russell observed during his survey published in 1878.
 

The same area in 1985 (photos from Pacific Aerial Survey in Oakland) with a lake level of 6380'. The lagoon has been dry since the 1950's when the lake dropped below 6405'. Note the sulphur pond again in the red box for easy identification. The dark gravelly beaches give way to the salt-encrusted clays and silts of the lake bed proper. Although difficult to see with the lack of depth perspective in this photo, a system of large, recent sand dunes has formed on the inland side of the dark gravelly beaches. These dunes were formed as a result of the greater reaches of wind-swept playa, providing a source of sand and the energy to move it. This sand dropped just to the lee of the large berm constructed of Black Point gravels--it is starting at this time to encroach into the dry lagoon. These surfaces were then available for colonization by plants beginning in the mid 1950's. Because the aeolian sediments from the lake bed are so saline and alkaline, few plants have been able to colonize--the sand dunes and other sandy surfaces are dominated by greasewood and saltgrass. The less salt-tolerant rabbitbrush does not occur until the first bank of inland dunes just above the dry lagoon in this picture.

The Mono Lake playa offered a remarkable opportunity to investigate the earliest stages of colonization by plants on the hostile playa surface. The salt-encrusted playa has a salinity of about 50 times that of sea water and a pH of around 11. No plant can establish under those conditions. However, in 1992 members of our research team discovered this isolated population of newly esablished greasewood, Sarcobatus vermiculatus, growing out on the playa, surrounded in both directions (lakeward and landward) by at least 500 m of hostile, barren salt crust. The population occurred on a small beach berm that was created during a winter storm, when higher energy waves sorted larger pumice particles and raised the berm on the surface of the salt-encrusted playa sometime in the mid 1980's. These small plants were thriving on the berm, not only because the large gravel-sized pieces of pumice allowed fresh water to be caught and stored but also because during the storm event, mats of brine shrimp and brine fly carcasses were rolled into the center of the berm. These characteristics of the berm provided plentifulrelatively fresh water and nitrogen for the establishing plants. Work by Kevin Fort, a master's student with Jim Richards, showed that seeds of all the dune-inhabiting species easily reached this isolated berm, given the strong basin downdraft winds from the vegetated dunes to the north. The loose gravels provided just the rough surface for seeds to be caught, and with all the favorable conditions combined, this population established apparently soon after the berm was formed. Here is the berm population in 1996; notice the lake encroaching to the left in the picture, as the lake level has risen from reduced water diversions and increased rainfall. This berm was completely inundated that winter, and we used this opportunity to excavate shrubs that had grown so large that overgrowth competition had occurred in the denser areas. This population was key in the study of shrub demography in determining whether true thinning occurs in desert perennial shrub populations.

Application:  This work is providing crucial information to support restoration of  the Owens Lake bed.  Since diversion of water from the Owens River, Owens Lake has been dry since early this century.  Over 100 square miles of dry, salt-encrusted playa like that at Mono Lake produce severe air pollution from dust exceeding EPA standards for PM10, arsenic and other toxic substances.  We propose that by manipulating natural ecosystem processes, natural vegetation can be restored on the presently barren Owens Lake playas, which will eliminate air pollution using a cost-effective, "walk away" solution that also meets public trust values in preserving California's natural environments.

This work was funded by NSF-FAW GER 90-23789 to Catherine Toft and USDA 92-37101-7419 to Catherine Toft, Deborah Elliott-Fisk and James H. Richards.

Publications:

• Toft, C.A. and D.L. Elliott-Fisk. 2002  Patterns of vegetation along a spatiotemporal gradient on shoreline strands of a desert basin lake. Plant Ecology 158: 212-39. PDF

Related studies:

• Brown, J.F. 1997. Effects of burial on survival, growth, and resource allocation of three species of dune plants. Journal of Ecology 85(2):151-158

• Donovan, L.A., J.H. Richards, and E.J. Schaber. 1997.   Nutrient relations of the halophytic shrub, Sarcobatus vermiculatus, along a soil salinity gradient. Plant and Soil 190: 105-117.

• Fort, K.P. and J.H. Richards. 1998. Does seed dispersal limit initiation of primary succession in desert playas? American Journal of Botany 85:1722-1731.
   

Abstracts

• Toft, C.A., D.L. Elliott-Fisk, and G.L. Schmid.  Development of late Holocene sand-dune ecosystems rimming Mono Lake:  Influence of hydrologic, geomorphic, and biological interactions. In:  Hall C.A., Jr. V. Doyle-Jones and B. Widawski. (eds.) The history of water: eastern Sierra Nevada, Owens Valley, White-Inyo Mountains.  White Mountain Research Station Symposium, University of California, Los Angeles. 4: 442.

• Elliott-Fisk, D. L., Toft, C. A., and Richards, J. H.  1993.  Development of late Holocene shoreline ecosystems at Mono Lake, California.  Association of American Geographers, Annual Meeting Abstracts, Atlanta GA.

• J.H. Richards, L.A. Donovan, K.P. Fort, E.J. Schaber and C.A. Toft. 1994.  Rapid establishment of shrubs on a recently exposed desert playa, Mono Lake, CA, (abstract). Bulletin of the Ecological Society of America (Supplement) 75:193.

Toft Home Page