Arundo donax L. (Poaceae) is an invasive, perennial grass that grows in many-stemmed, cane-like clumps. It does not produce viable seeds in California and is currently thought to invade habitats rapidly by rhizomes and fragments only. But, during a two-year field study in the Tijuana River Valley, California, expansion of A. donax clumps via rhizomes was slow, only 0.29 m 2 yr⁻¹, and new recruits from fragments were rare, only 4.7 ha⁻¹ yr⁻¹. Whereas layering, a mode of spread heretofore ignored by researchers, was common in the flood zone. Layering is the adventitious sprouting of stem tips in contact with the ground. Layering can be considered to be both expansion of a clump (while the layering stem is still alive and attached to the clump) and asexual reproduction (after the layering stem dies). When viewed as clump expansion, layering was 7.4 times faster than the annual expansion via rhizomes. When viewed as reproduction, layering produced 25 times more new recruits than fragments. Layering was therefore an important means by which A. donax was spreading within the flood zone.

A new general view of A. donax invasion is presented illustrating that fragmentation is the means by which A. donax invades a new site in the flood zone, expansion via rhizomes maintains an A. donax clump, and layering is the means by which A. donax spreads quickly and episodically within the flood zone. Outside the flood zone, A. donax expands slowly via rhizomes only and no new recruits arrive from either fragmentation or layering.

The Tijuana River Valley results challenge the current “top-down” management policy, which presumes that most new recruits come from upstream and that all clumps expand at the same rate. The results show that, on the contrary, most new recruits come from within the habitat, via layering, and that clumps in the flood zone expand faster than those outside the flood zone. I conclude that the top-down policy is counter-productive and suggest that managers shift to controlling A. donax “inside-out,” i.e., conduct treatments first inside and then outside the flood zone. In this way, the fastest expanding clumps – those in the flood zone – will be treated first.

Plant biomass and seed production were quantified for Brassica tournefortii Gouan, Brassicaceae (Sahara mustard) from 3 sites spanning the Mojave and Sonoran deserts, in the Southwestern United States. We found strong linear relationships between plant biomass and seed production, with larger plants producing more seeds per plant (R² = 0.93) and greater seed biomass per plant (R² = 0.94). Both seed count (R² = 0.93) and seed biomass (R² = 0.90) were also greater in 0.25 m² plots that had higher plant biomass. These results and the law of constant final yield indicate that biomass and seed production of individual Sahara mustard plants can be higher in plots with lower densities. These data suggest that control efforts that do not remove all individuals may reduce densities but inadvertently increase net seed production within treated areas.

Triteleia laxa (Themidaceae), a liliaceous geophyte common in California at lower elevations with mediterranean climate, was studied during 1998–2004 at four sites in the northern Sacramento Valley. New individual plants were randomly selected each year at one to four of these grassland or open savanna sites to provide a composite study of the biology and life history of the plant. A mature plant produced two leaves after fall rains begin, a new corm on top of the shrinking old corm in spring, and a scape with an umbel of large bluish flowers in late March or April. By seed production in May, above-ground parts were dead, and the new corm and seeds persisted through summer. Mean leaf lengths varied from 22 to 28 cm; no correlation was found with amount of precipitation. Mean scape lengths also varied, from 23 to 32 cm; overall, there was a negative correlation with spring precipitation. Corms of flowering plants had a mean volume of 1.30 cm³, and occurred at a mean depth of 7.27 cm; corm volume was correlated with scape height and with number of flowers. Dry mass increased linearly in the new corm during the spring growth period. Number of flowers per plant varied among sites and the mean varied highly significantly among 5 yr (range 8–12.6). Plants appeared to be largely self-incompatible, but produced a small number of selfed seeds when pollinated by hand. The pollen∶ovule ratio was about 3100∶1. Mean fruit set (range 50–74%) and mean seed set (range 40–58%) were low, and varied significantly among sites and years. Seed mass averaged about 1.7 mg, and seeds showed 100% viability. Germination time was about 4 wk after wetting, with up to 98% of seeds germinating. The seedling was carried downward from the seed by the elongating cotyledon, ultimately producing a single foliage leaf, a lateral contractile root that shortened in April (and in situ doubtless pulls the seedling deeper into the soil), and a corm <4 mm in diameter. Soils occupied in study sites were loams, with 20 to 39% clay particles. This study on T. laxa gives a reasonably complete picture of the biology for a common geophyte, and we hope that this work will provide impetus for additional studies of other widespread or local geophytes.

Giant sequoia (Sequoiadendron giganteum) seedling survival was nearly seven (6.78) times greater in heavily charred soils than in non-burned soils 34 and 35 yr after the first experimental burns in Kings Canyon National Park, California, and the first such management burns in any western national park. Tree height, especially trees growing in intensely burned areas, was found to be highly correlated with sunlight and less so with moisture. Moisture and light were important to establishment of giant sequoias but continued growth of these trees in the first four decades of life appears to be more dependent on high levels of sunlight. Surveyed vegetation and downed wood indicated that 35 yr after management burns stand structure has developed to the point where the management areas are susceptible to destructive crown fires.

Tree ring fire-scars in Sequoiadendron giganteum (giant sequoia) stands record a high frequency, low intensity, prehistoric fire regime. Difficulties achieving short prehistoric fire return intervals with prescribed burns at a S. giganteum stand in Calaveras Big Trees State Park, California, currently characterized by dense tree cover with little understory vegetation due to over a century of fire suppression, suggest that a prehistoric grass understory provided fine fuel required for frequent fire spread. We used phytolith analysis to test this hypothesis. Phytoliths, microscopic silica bodies found in many plants but produced in large quantities with distinctive morphotypes in grasses, are preserved for thousands of years in the soil. Soils under vegetation with extensive prehistoric grass cover retain a high concentration of grass phytoliths regardless of historic vegetation changes. Phytoliths were extracted from soil samples taken from pits dug at 14 plots throughout a S. giganteum stand in the South Grove Natural Preserve. Soil phytolith weight for most plots, currently without grass cover and comprising most of the stand, was less than 0.10%, consistent with reported values for forests with no grass in the understory. Soil phytolith weights for ridge-top plots and plots near the stream channel were significantly higher, suggesting localized areas with sparse grass cover. The hypothesis that there was substantial prehistoric grass cover in this S. giganteum stand was rejected.

Although widespread throughout the interior foothills of central and northern California, Pinus sabiniana Dougl. has a disjunct distribution in the southern Sierra Nevada, where it is abundant in the Kern River and Tule River watersheds, but is absent from the Kaweah River watershed between 36° and 37°N. This gap in the pine's distribution has long intrigued botanists and ecologists and has elicited a number of hypotheses for this anomalous biogeographical pattern. Here we propose a new hypothesis that couples unique features of the southern Sierra Nevada topography with unique features of P. sabiniana's response to fire. This low elevation pine is widely distributed in grassland and chaparral, and where it occurs with the latter vegetation, it is extremely vulnerable to high intensity wildfires. Under these conditions, meta-populations persist over time in refugia in riparian areas and during fire-free intervals expand outwards re-colonizing shrubland dominated slopes. The lack of such refugia in the very steep and narrow Kaweah drainage is hypothesized to explain the absence of this pine in that area. To test this hypothesis, we studied the age-structure of P. sabiniana in the area of the 2002 McNally Fire in the Kern drainage to compare age distributions of trees and tree skeletons along a gradient up slope away from riparian zones. Maximum age declined significantly with distance from riparian areas, suggesting that past fires have eliminated P. sabiniana from the slopes and that the pines have re-colonized during fire-free intervals. The relationship was strongest when our data were restricted to areas that had a previously recorded fire. We also found that the riparian areas in the Kern drainage were significantly wider than those in Kaweah drainage, suggesting that fewer such fire refugia exist in the latter watershed, and providing an explanation for the lack of P. sabiniana between 36° and 37°.

Postfire resprouting by woody plants confers a marked advantage in rate of recovery over species that regenerate entirely from seed. However, the predictability of this advantage varies markedly between species, with some showing nearly 100% rootcrown survival and others often much lower. This study examined patterns of fire-caused mortality and tested the relative importance of fire severity and plant age between various shrubs and subshrubs characteristic of chaparral and sage scrub associations. Resprouting success varied from about 10% for Eriogonum fasciculatum to a high of 98% for Quercus berberidifolia. For most of the shrub species, skeletons of resprouting plants were significantly taller than those of dead individuals of the same species, indicating less biomass consumption, and thus lower severity fires were associated with higher resprouting success. This pattern was less strongly the case with sage scrub species. Shrubs and subshrubs, however, differed in the effect of aboveground plant age (as estimated by basal diameter) on resprouting success. For most chaparral shrubs, age was not related to resprouting success, whereas in four out of five subshrub species, including Artemisia californica, Eriogonum fasciculatum, Salvia leucophylla, and S. mellifera, the youngest plants exhibited the highest resprouting success. I hypothesize that the reason for this inverse relationship between age and resprouting in certain sage scrub species is that, as these subshrubs age, there is a tendency to loose the resprouting ability and the mechanism is quite possibly because adventitious buds responsible for sprouting become buried by woody tissues. Patterns of character evolution in these sage scrub lineages support the hypothesis that the herbaceous perennial mode of seasonal aestivation evolved early and lignification is a more recently derived trait and this may have negative effects on resprouting as the plant ages.

Fremontias, or flannel bushes (Fremontodendron), are a distinctive element of California's chaparral communities. Fremontodendron decumbens is only known from a few populations in gabbro soil plant communities of the Sierra Nevada foothills in El Dorado County. Although a recovery plan for these communities has been drafted, the long-term management of F. decumbens is complicated by its treatment as a subspecies of the more widespread F. californicum, and by the recent discovery of additional populations of decumbent plants in Yuba and Nevada Counties that are not easily assigned to either F. californicum or F. decumbens. Genetic relationships among 5 populations, including F. californicum, F. decumbens, and the decumbent plants in Yuba County, were ascertained using AFLP markers. Principal coordinates and population structure analyses of the AFLP data showed that F. decumbens is genetically distinguishable from the populations of F. californicum that we sampled. This distinction, coupled with its unique morphology and ecology, support the treatment of F. decumbens as a species and promote its continued conservation as a rare and unique element of plant communities on gabbro soils in the Sierra Nevada. The decumbent Yuba County population shared a number of alleles with F. californicum and F. decumbens and the analyses did not clearly distinguish its taxonomic relationships. It is possible that this population represents an historical hybrid between F. californicum and F. decumbens. A resolution of the taxonomic position of the decumbent Yuba County populations will require more thorough sampling of F. californicum but the presence of unique alleles in this population suggests that it also should be conserved.

A multivariate analysis was performed for populations of Echinocereus (section Triglochidiatus) to facilitate the taxonomic circumscription of E. arizonicus subsp. arizonicus. Twenty-one morphological characters for 16 populations evidenced the validity of at least two subspecific taxa within E. arizonicus: E. arizonicus subsp. arizonicus and E. arizonicus subsp. nigrihorridispinus. Principle components analysis indicated that stem characters were most diagnostic in defining two distinct groups of populations, each including the type locality of one of the two subspecies. Unweighted pair group method with arithmetic mean (UPGMA) clustered populations of the two subspecies apart from one another and from those of the outgroup, E. triglochidiatus subsp. mojavensis. For most measured characters, means differed significantly between the two subspecies. Discriminant analysis correctly classified 97.0% for individuals of E. arizonicus subsp. arizonicus and 94.7% for individuals of E. arizonicus subsp. nigrihorridispinus, compared to an overall 97.8% correct classification of individuals for all perfect-flowered taxa of section Triglochidiatus investigated.

Two hornworts, five liverworts, and 24 mosses are reported new for the state of Nevada. The phylum Anthocerotophyta as represented by the families Anthocerotaceae and Notothyladaceae, the liverwort families Antheliaceae, Cleveaceae, Fossombroniaceae, and Pseudolepicoleaceae, and the moss family Bruchiaceae are all new for the state. Genera new for Nevada include: Anthelia, Anthoceros, Athalamia, Blepharostoma, Bruchia, Codriophorus, Conostomum, Ditrichum, Fossombronia, Gemmabryum, Phaeoceros, Ptychostomum, and Rosulabryum. A new treatment of the widespread Bryum caespiticium Hedwig is adopted for North America, with the segregates Bryum badium (Bridel) W. P. Schimper and Bryum kunzei Hornschuch reported for the first time for North America.

A new species of Hesperolinon is described that is distinguished by its morphology, particularly its three carpels and styles, dichasial inflorescence, and certain petal characteristics. It is a serpentine endemic and may be related to Hesperolinon bicarpellatum.