Evolution, Ecology and Floristics in Northern California - Current Knowledge and Unexplored Realms
Schlising, Robert A. .
Demographics over 21 years for a population of Chamaesyce hooveri (Euphorbiaceae), across three habitats within one large vernal pool.
CALIFORNIA'S mediterranean vernal pools often occur at low-elevations, where a hardpan layer in or under the soil permits accumulation of winter rainfall. Springtime evaporation of water causes desiccation in the pool basins. A pool 290 m long, in the Nature Conservancy’s Vina Plains Preserve north of Chico, was used to study a rare (federally “threatened”) summer-annual restricted to this habitat. Chamaesyce hooveri (Wheeler) Koutnik grows as a prostrate mat; it is extremely variable in size, and produces up to hundreds of small inflorescences with oozing nectaries that attract insects. This study began in 1984, when it became apparent that one population of this species was distributed across several different zones of vegetation within the pool. A permanent 5m x 10m plot was set up in each of three zones. Plants were censused and measured close to 25 July each summer for 21 years to investigate if numbers and sizes of Chamaesyce plants differed in relation to vegetation/soil zone and/or with weather of the year. A remarkable array of highly significant differences is found in both plant numbers and sizes when 1) years are compared for one plot, and 2) when the three plots are compared for one year. Causes for this variation are not all identified, but several abiotic and biotic features are implicated with varying degrees of certainty. These include 1) total yearly precipitation, 2) duration of standing water, 3) amount of organic matter in the soil, 4) native species—a clonal spikerush (Eleocharis), a grasshopper (Melanoplus) and a bird (Eremophila), and 5) invasive, exotic plants (Convolvulus and Xanthium). Variations within one population show this obscure little plant as a dynamic and plastic annual that could serve as subject for diverse environmental studies within large vernal pools like this.
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1 - California State University Chico, Department of Biological Sciences, Chico, California, 95929-0515, USA
Presentation Type: Symposium or Colloquium Presentation
Date: Tuesday, August 1st, 2006
Time: 10:15 AM