December 2004 CA Grassland Newsletter
1) CNGA ballots
2) Recent publications
1) Janice Bridge reminds CNGA members to send in their ballots for the current election. Along with votes for officers, there is a proposed change in the name to the California Native *Grassland* Association.
2) Recent publications:
By popular demand, I'm including abstracts for the recent papers, where available...
Enloe, DiTomaso, Orloff, and Drake. 2004. Soil water dynamics differ among rangeland plant communities dominated by yellow starthistle (Centaurea solstitialis), annual grasses, or perennial grasses. Weed Science 52(6): 929-935
California's interior grasslands have undergone dramatic changes during the last two centuries. Changes in land-use patterns and plant introductions after European contact and settlement resulted in the conversion of perennial-dominated grasslands to exotic annual grasses. More recently, the annual grasslands have been heavily invaded by the deeply rooted late-maturing forb yellow starthistle. This series of invasions and conversions has changed the community structure and phenology of the grasslands. We hypothesized that these changes have resulted in significant differences in soil wateruse patterns in the grasslands. We studied soil water depletion and recharge patterns of three grassland community types dominated by perennial grasses, annual grasses, or yellow starthistle with contrasting phenology and rooting depths for 4 yr. Soil moisture measurements were taken every month from March to December in 1998, 1999, and 2000 and every other month in 2001. Measurements were taken with a neutron probe at depths of 30 to 150 cm at 30-cm intervals. The results indicate that the yellow starthistle community maintained a significantly drier soil profile than the annual grass community. The perennial grass community maintained an intermediate soil water content that was not significantly different from either of the other two communities. Significant time by community and depth by community interactions indicated that the yellow starthistle community continued depleting soil moisture later into the season and at deeper depths than the other grass communities. This study demonstrates the effect of plant invasion on soil water recharge and depletion patterns in California grasslands.
Zavaleta and Hulvey. 2004. Realistic species losses disproportionately reduce grassland resistance to biological invaders. Science 306: 1175-1177.
Consequences of progressive biodiversity declines depend on the functional roles of individual species and the order in which species are lost. Most studies of the biodiversity-ecosystem functioning relation tackle only the first of these factors. We used observed variation in grassland diversity to design an experimental test of how realistic species losses affect invasion resistance. Because entire plant functional groups disappeared faster than expected by chance, resistance declined dramatically with progressive species losses. Realistic biodiversity losses, even of rare species, can thus affect ecosystem processes far more than indicated by randomized-loss experiments.
Vreeland, Justin K. and William D. Tietjie. 2004. Vegetative structure of woodland-grassland edges in coastal central California. Southwestern Naturalist 49:305-310.
Most research on effects of edges to vertebrate wildlife comes from eastern-deciduous, boreal, and tropical forests where most edges are abrupt and have resulted from anthropogenic forest fragmentation. California oak (Quercus) woodland, by contrast, is naturally patchy and contains abundant edges, constituting a naturally fragmented vegetative complex. No published research has characterized the vegetative structure of these natural edges in California oak woodlands. To begin to fill this information gap, we measured 10 vegetative characteristics and the number of dusky-footed woodrat (Neotoma fuscipes) dwellings on 8 edges at 4 oak-grassland sites in San Luis Obispo County, California. Stem density and shrub cover were less at edges. Canopy cover and tree diameter were greater at edges, but other vegetative characteristics were similar between the edges of the woodland stands and their interiors. Woodrat dwellings were equally abundant between edges and interiors. Concepts of nest predation, nest parasitism, and other deleterious effects of induced edges previously identified in contiguous-canopy forests might not be applicable to California oak woodlands. Further research is needed to assess wildlife response to oak woodland edges and to further quantify vegetation characteristics of natural and induced oak woodland edges at stand and landscape scales.
Cushman, Tierney, and Hinds. 2004. Variable effects of feral pig disturbance on native and exotic plants in a California grassland. Ecological Applications 14:1746-1756.
ABSTRACT. - Biological invasions are a global phenomenon that can accelerate disturbance regimes and facilitate colonization by other nonnative species. In a coastal grassland in northern California, we conducted a four-year exclosure experiment to assess the effects of soil disturbances by feral pigs (Sus scrofa) on plant community composition and soil nitrogen availability. Our results indicate that pig disturbances had substantial effects on the community, although many responses varied with plant functional group, geographic origin (native vs. exotic), and grassland type. ("Short patches" were dominated by annual grasses and forbs, whereas "tall patches" were dominated by perennial bunchgrasses.) Soil disturbances by pigs increased the richness of exotic plant species by 29% and native taxa by 24%. Although native perennial grasses were unaffected, disturbances reduced the biomass of exotic perennial grasses by 52% in tall patches and had no effect in short patches. Pig disturbances led to a 69% decrease in biomass of exotic annual grasses in tall patches but caused a 62% increase in short patches. Native, nongrass monocots exhibited the opposite biomass pattern as those seen for exotic annual grasses, with disturbance causing an 80% increase in tall patches and a 56% decrease in short patches. Native forbs were unaffected by disturbance, whereas the biomass of exotic forbs increased by 79% with disturbance in tall patches and showed no response in short patches. In contrast to these vegetation results, we found no evidence that pig disturbances affected nitrogen mineralization rates or soil moisture availability. Thus, we hypothesize that the observed vegetation changes were due to space clearing by pigs that provided greater opportunities for colonization and reduced intensity of competition, rather than changes in soil characteristics. In summary, although responses were variable, disturbances by feral pigs generally promoted the continued invasion of this coastal grassland by exotic plant taxa.
McClung, William J. 2004. Twice-annual cutting to support native grasslands in the Berkeley Hills: Ten years, four examples. Grasslands 14: 6-8. (No abstract)
Morghan, Kimberly Reever 2004. The ecology of Aristida ternipes var hamulosa and Aristida oligantha in northern California and Oregon. Grasslands 14: 8-11. (NO abstract).