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The giant sequoia, a serotinous conifer naturally occurring in mixed‐conifer forests of the southern and central Sierra Nevada, California, USA, is the world's largest tree species. Giant sequoia reproduction has been severely lacking over the past century, due to fire exclusion, creating a significant conservation threat. Previous research on postfire sequoia reproduction in high‐severity fire areas, relative to low‐ and moderate‐severity areas, is limited. At 6 years postfire, we investigated giant sequoia reproduction in a high‐severity fire area, and nearby low‐/mixed‐severity fire areas, in the Nelder Grove, which burned in 2017 in the Railroad fire. Postfire giant sequoia reproduction was positively correlated with fire severity in terms of density, height (growth), and proportion (relative to other conifer species), and sequoia seedling/sapling density was positively correlated with percent shrub cover. There was no correlation between distance to live sequoia seed source and density of sequoia reproduction. More research is needed in other mixed‐severity fire areas, with larger high‐severity fire patches, to determine whether a similar postfire response occurs elsewhere. [ABSTRACT FROM AUTHOR]

Plants interact extensively with their neighbors, but the evolutionary consequences of variation in neighbor identity are not well understood. Seedling traits are likely to experience selection that depends on the identity of neighbors because they influence competitive outcomes. To explore this, we evaluated selection on seed mass and emergence time in two California grasses, the native perennial Stipa pulchra , and the non-native annual Bromus diandrus , in the field with six other native and non-native neighbor grasses in single- and mixed-species treatments. We also quantified characteristics of each neighbor treatment to further investigate factors influencing their effects on fitness and phenotypic selection. Selection favored larger seeds in both focal species and this was largely independent of neighbor identity. Selection generally favored earlier emergence in both focal species, but neighbor identity influenced the strength and direction of selection on emergence time in S. pulchra , but not B. diandrus. Greater light interception, higher soil moisture, and greater productivity of neighbors were associated with more intense selection for earlier emergence and larger seeds. Our findings suggest that changes in plant community composition can alter patterns of selection in seedling traits, and that these effects can be associated with measurable characteristics of the community. [ABSTRACT FROM AUTHOR]

Many studies of community assembly focus on a single ontogenetic stage (typically adults) when trying to infer assembly processes from patterns of biodiversity. This focus ignores the finding that assembly mechanisms may strongly differ between life‐stages, and the role of ontogenetic dependency: the mechanisms by which one life stage directly affects the composition of another life stage.Within a 4‐ha forest dynamics plot in California USA, we explored how the relative importance of multiple assembly processes shifts across life stages and assessed ontogenetic dependency of seedlings on adults in woody plant communities. To assess variation in assembly processes across life stages, we examined how β‐diversity of adult and seedling communities were each influenced by space and 13 environmental variables (soils, topography) using distance‐based redundancy analysis and variation partitioning. We then assessed the ontogenetic dependency of seedlings on adults by including adult composition as a predictor in the seedling community variation partitioning.We found differences between adult and seedling composition. For the adults, we found 18 species including pines, oaks and manzanitas characteristic of this mid‐elevation forest. For seedlings, we found 11 species, and that oaks made up 75% of all seedlings while only making up 45% of all adults. Adult β‐diversity was primarily explained by space (44.0%) with environment only explaining 18.6% and 37.4% unexplained. In contrast, most of the explained variation in seedling β‐diversity was due to ontogenetic dependency alone (13.6% explained by adult composition) with 1.6% explained by space and the environment jointly, and 62.8% unexplained.Synthesis: Here, we describe a conceptual framework for integrating ontogeny more explicitly into community assembly research and demonstrate how different assembly processes structured adult and seedling β‐diversity in a temperate dry forest. While adult β‐diversity was largely driven by spatial processes, seedling β‐diversity was largely unexplained, with ontogenetic dependency comprising most of the explained variation. These patterns suggest that future assembly research should consider how assembly processes and their underlying mechanisms may shift with ontogeny, and that interactions between ontogenetic stages (ontogenetic dependency) are critical to consider when assessing variation in assembly processes. [ABSTRACT FROM AUTHOR]

The larval stages of cabbage maggot, Delia radicum (L.) (Diptera: Anthomyiidae), attack the roots of cruciferous crops and often cause severe economic damage. Although lethal insecticides are available to control D. radicum, efficacy can be improved by the placement of residues near the roots where the pest is actively feeding and causing injury. One such method is drenching seedlings with insecticide before transplanting, referred to as "tray drench." The efficacy of insecticides, when applied as tray drench, is not thoroughly understood for transplants of broccoli and cauliflower. Thus, a series of seedling tray drench trials were conducted on transplants of these 2 vegetables using cyantraniliprole, chlorantraniliprole, clothianidin, bifenthrin, flupyradifurone, chlorpyrifos, and spinetoram in greenhouse and field settings. In the greenhouse trials, the severity of D. radicum feeding injury was significantly lower on broccoli and cauliflower transplants when drenched with clothianidin, bifenthrin, and cyantraniliprole compared with untreated controls. In broccoli field trials, incidence and severity of feeding injury was lower in seedlings drenched with cyantraniliprole and clothianidin, as well as a clothianidin spray at the base of seedlings, than the use of spinetoram, chlorpyrifos, flupyradifurone, and chlorantraniliprole. In a cauliflower field trial, tray drench application of cyantraniliprole significantly reduced the severity of D. radicum feeding injury in seedlings than untreated controls. Also, the fresh weight of plant shoots was significantly greater in cyantraniliprole tray drenched plants than untreated controls. In a different tray drench trial with cauliflower, the severity of cabbage maggot injury was significantly lower on plants that received cyantraniliprole at wide plant spacing of 30.5 cm (high dose) than narrow spacing of 17.8 cm (low dose) compared with untreated controls. The implications of these results on D. radicum management for transplanted cruciferous crops and impact on the environment are discussed. [ABSTRACT FROM AUTHOR]

Drought is a major stress for plants, creating a strong selection pressure for traits that enable plant growth and survival in dry environments. Many drought responses are conserved species‐wide responses, while others vary among populations distributed across heterogeneous environments. We tested how six populations of the widely distributed California valley oak (Quercus lobata) sampled from contrasting climates would differ in their response to soil drying relative to well‐watered controls in a common environment by measuring ecophysiological traits in 93 individuals and gene expression (RNA‐seq) in 42 individuals. Populations did not differ in their adjustment of turgor loss point during soil drying, suggesting a generalized species‐wide response. Differential expression analysis identified 689 genes with a common response to treatment across populations and 470 genes with population‐specific responses. Weighted gene co‐expression network analysis (WGCNA) identified groups of genes with similar expression patterns that may be regulated together (gene modules). Several gene modules responded differently to water stress among populations, suggesting regional differences in gene network regulation. Populations from sites with a high mean annual temperature responded to the imposed water stress with significantly greater changes in gene module expression, indicating that these populations may be locally adapted to respond to drought. We propose that this variation among valley oak populations provides a mechanism for differential tolerance to the increasingly frequent and severe droughts in California. [ABSTRACT FROM AUTHOR]

Mediterranean oak woodlands are currently undergoing considerable anthropogenic changes that globally threaten their long‐term persistence. Restoration efforts via assisted regeneration depend on species traits and type of stress. However, how different sources of stress vary across space (microsites) and time (intra‐ and inter‐annual variation) for co‐occurring oak species remains largely unknown.We examined spatio‐temporal variation of biotic (herbivory, seed predation) and abiotic (drought) stress agents to evaluate seedling survival across different regeneration microsites, and considering two climatically contrasting years. We used two co‐occurring species of contrasting ecology and leaf traits in California oak woodlands: the deciduous Quercus lobata (valley oak) and the evergreen Q. agrifolia (coast live oak).Most oak seedlings (98.8%) suffered from some type of stress. For both species, summer drought was the main cause of mortality, followed by rodent damage, ungulate browsing and insect damage. Rodents represented the predominant biotic stress, as all rodent‐affected seedlings eventually died. Interactions among stress factors were nuanced: insect and ungulate‐browsing stresses were greater during dry year, whereas rodent damage was similar in dry and average years. Intra‐annually, rodent damage was the main stress agent in early spring, whereas water stress and ungulate‐browsing were greater from late spring to early fall. Plant species traits were also determinant: overall, the evergreen species had greater survival probability than the deciduous one.Across microsites, water stress showed higher occurrence in open grassland habitats, while rodent damage was prevalent under palatable shrubs and ungulate browsing under conspecific trees. Shrub and tree cover reduced damage attributed to water stress but increased rodent and ungulate damage, respectively. Interestingly, lower water stress but higher rodent damage was found further inside the shrub cover.Synthesis and applications. Intra‐ and inter‐annual variation are critical determinants of stress type and intensity on oak recruitment. Spatial variation (microsite identity) is highly useful to manipulate stress agent impact. We conclude that assisted regeneration should consider not only the predominance and lethality of each stress type and microsite, but also the interactions thereof and thus manipulate protective microsites accordingly. [ABSTRACT FROM AUTHOR]

Using nurse plants to facilitate native plant recruitment in degraded habitats is a common restoration practice across various arid and semiarid environments. Living trees or shrubs are typically considered nurse plants, whereas dead shrubs left in the landscape from prolonged drought are understudied prospective facilitators for native plant recruitment. The interaction between nurse plants and biotic pressures, such as herbivory, on native recruitment is also not well understood in semiarid plant communities. We investigated the effects of facilitation and herbivory on native seedling germination, growth, and survival in the restoration of degraded coastal sage scrub (CSS) habitat. Native shrub seedlings (Artemisia californica and Salvia mellifera) were planted, and native annual species (Amsinckia intermedia, Deinandra fasciculata, Phacelia distans, and Pseudognaphalium californicum) were sown in three Shrub Type treatments (live shrub, dead shrub, and exposed areas), with a nested Cage treatment (no cage and cage) in each Shrub Type treatment. Annual species grew equally well in all Shrub Type treatments; shrub seedlings grew largest in exposed areas. While there was little evidence of facilitation for all species tested, there were strong positive effects of caging on growth and establishment of all species. Caging palatable native species or planting species with anti‐herbivory traits around target plants may be more strategic approaches compared to using nurse plants in restoring degraded CSS after extended drought. [ABSTRACT FROM AUTHOR]

The principal objective of this study was to determine the etiology of a canker disease in dormant stone fruit and apple tree seedlings maintained in refrigerated storage that has significantly impacted California fruit and nut tree nurseries. Signs and symptoms of the disease develop during storage or soon after planting, with subsequent decline and death of young trees. Isolations from both diseased and healthy almond and apple trees and Koch's postulates using stem segments of desiccation-stressed almond trees as hosts implicated Fusarium avenaceum and F. acuminatum as the primary causal agents. F. solani, Ilyonectria robusta, and Cylindrocarpon obtusiusculum were also capable of causing similar symptoms but were less frequently encountered in isolations of diseased tissue. Loss of bark turgidity in excised almond stem segments, as can occur in cold-stored seedlings, correlated with increased susceptibility to F. acuminatum, with maximum canker development occurring after relative bark turgidity dropped below a threshold of approximately 86%. Healthy almond trees, almond scion budwood, and a wheat cover crop used in fields where tree seedlings were grown and maintained until cold storage all possessed asymptomatic infections of F. acuminatum, F avenaceum, and C. obtusiusculum as determined by activation following overnight freezing, cold storage, or desiccation. [ABSTRACT FROM AUTHOR]

Thinning implemented with a cut-to-length harvesting system coupled with on-site slash mastication and redistribution and followed by prescribed underburning were evaluated for their impacts on seedling and sapling demography in an uneven-aged, eastern Sierran mixed conifer stand. Species composition consisted of California white fir (Abies concolor var. lowiana [Gord.] Lemm.), Jeffrey pine (Pinus jeffreyi Grev. & Balf.), sugar pine (Pinus lambertiana Dougl.), incense-cedar (Libocedrus decurrens Torr.), and red fir (Abies magnifica A. Murr.), but the former was preponderant in both the overstory and regeneration. The mechanized treatments facilitated the establishment of white and red fir and incense-cedar seedlings more so than those of Jeffrey and sugar pine, but sapling losses incurred from their implementation were severe and largely of white fir. Prescription fire promoted the establishment of Jeffrey pine seedlings, and to a lesser degree those of white fir, over incense-cedar and red fir, while it diminished sapling abundance in the absence of the mechanized treatments and essentially eliminated this size class when preceded by them, with sapling losses again largely white fir. Continuous establishment of natural regeneration and its survival are essential in perpetuating an uneven-aged forest structure, and these results provide land managers insight into the impacts of treatments designed for sensitive sites on seedlings and saplings in eastern Sierra Nevada mixed conifer and similar forest types. [ABSTRACT FROM AUTHOR]

Apium virus Y (ApVY) is a potyvirus that was recently found to cause crop loss to celery (Apium graveolens) in California. Symptoms on leaves exhibit varying forms of chlorosis and necrosis. Depending on the cultivar, celery petioles could also exhibit extensive necrotic, sunken, elongated lesions. Severely affected plants were unmarketable. Disease incidence surveys found that a susceptible celery (cv. 414) showed 55% (2007) and 71 % (2008) disease. Because it was noted that the Apiaceae weed poison hemlock (Conium maculatum) was present in almost all areas where ApVY affected celery, a 4-year survey collected overwintered hemlock from six coastal county regions and tested composite samples for ApVY using reverse transcription-polymerase chain reaction (RT-PCR) and ApVY-specific primers. These plants were consistently positive for ApVY. Seeds collected from these plants were also positive when tested with the same RT-PCR method. However, when ApVY-positive hemlock seeds were germinated and the resulting seedlings tested, all results were negative. The failure of ApVY tobe transmitted from hemlock seeds to seedlings was further documented by collecting newly germinated hemlock seedlings from the field and testing them with RT-PCR. All such seedlings were negative for ApVY even though large, adjacent, overwintered hemlock plants tested positive. Two crops of celery seed were produced from ApVY-positive mother plants; celery seed from these infected plants likewise tested positive for ApVY, but seedlings grown from the seed lots were negative for ApVY. Twenty-one celery and celeriac cultivars were inoculated with ApVY using viruliferous aphids, planted in a replicated field trial, and then grown to maturity. Seven cultivars remained symptomless, tested negative for ApVY, and showed signs of possible resistance. The epidemiology of disease caused by ApVY in California evidently involves poison hemlock as a common overwintering host with subsequent vectoring of the virus from hemlock to celery via aphids. ApVY was not seedborne in this weed host or in celery in our experiments. Our data suggest that growers can manage this disease by controlling poison hemlock weed populations and by planting celery cultivars that are not susceptible to ApVY [ABSTRACT FROM AUTHOR]

Cyanobacteria and algae are problematic in California rice fields that are typically shallow and have high nutrient levels, providing ideal growing conditions. Nostoc spongiaefbrme is a problem because extensive floating mats dislodge rice seedlings or smother them when the mats accumulate in windward areas. There is little published information on growth requirements for N. spongiaeforme. We grew N. spongiaeforme in BG-11 medium at 24 combinations of light (22, 87, 162, and 400 µM m-2s-1) and temperatures (10°C, 15°C, 20°C, 25°C, 30°C, and 35°C). Results were summarized as a quadratic equation relating light and temperature to growth and indicate that optimal growth occurred at 26°C and 227 µM m-2)s-1) of light. Thus, N. spongiaeforme grows well at water temperatures and light levels similar to those measured in rice fields during the critical 30 days following initial flooding of the field. [ABSTRACT FROM AUTHOR]

Changes in plant inputs under changing atmospheric CO2 can be expected to alter the size and/or functional characteristics of soil microbial communities which can determine whether soils are a C sink or source. Stable isotope probing was used to trace autotrophically fixed 13C into phospholipid fatty acid (PLFA) biomarkers in Mojave Desert soils planted with the desert shrub, Larrea tridentata. Seedlings were pulse-labeled with 13CO2 under ambient and elevated CO2 in controlled environmental growth chambers. The label was chased into the soil by extracting soil PLFAs after labeling at Days 0, 2, 10, 24, and 49. Eighteen of 29 PLFAs identified showed 13C enrichment relative to nonlabeled control soils. Patterns of PLFA enrichment varied temporally and were similar for various PLFAs found within a microbial functional group. Enrichment of PLFA 13C generally occurred within the first 2 days in general and fungal biomarkers, followed by increasingly greater enrichment in bacterial biomarkers as the study progressed (Gram-negative, Gram-positive, actinobacteria). While treatment CO2 level did not affect total PLFA-C concentrations, microbial functional group abundances and distribution responded to treatment CO2 level and these shifts persisted throughout the study. Specifically, ratios of bacterial-to-total PLFA-C decreased and fungal-to-bacterial PLFA-C increased under elevated CO2 compared with ambient conditions. Differences in the timing of 13C incorporation into lipid biomarkers coupled with changes in microbial functional groups indicate that microbial community characteristics in Mojave Desert soils have shifted in response to long-term exposure to increased atmospheric CO2. [ABSTRACT FROM AUTHOR]

Herbivores can affect the composition of grassland communities. We examined seedling herbivory by the introduced snail, Helix aspersa, on four grass species common in California grasslands. To assess preference, standardized tests using equal amounts of seedlings of the same age were conducted in addition to tests in which live seedlings were exposed to snail herbivory. Helix aspersa exhibited the greatest preference for native Bromus carinatus, while native Nassella pulchra and exotic B. hordeaceus were moderately preferred. Exotic Avena fatua was least preferred. Assessment of preference using both standardized and live seedling trials yielded consistent results, suggesting that preference is due to variation in seedling quality rather than differences in per-seedling biomass that are likely to exist under field conditions. Avena fatua is very common in California grasslands while B. carinatus is relatively rare. Our results suggest that the high level of snail preference for B. carinatus and aversion to A. fatua, coupled with severe effects on future growth due to complete defoliation of live seedlings, may reinforce patterns of establishment of these grasses observed in natural communities. [ABSTRACT FROM AUTHOR]

Avocado (Persea americana Mill.) has an unusual flowering mechanism, diurnally synchronous protogynous dichogamy, that promotes crosspollination among avocado genotypes. In commercial groves, which usually contain pollinizer rows adjacent to the more desirable commercial cultivars, the rate of outcrossing has been measured with variable results. Using microsatellite markers, we estimated outcrossing in a commercial California 'Hass' avocado orchard with adjacent 'Bacon' pollinizers. Seedlings grown from mature harvested fruit of both cultivars were genotyped with five fully informative microsatellite markers and their parentage determined. Among the 919 seedlings of 'Hass', 688 (75%) were hybrids with 'Bacon'; the remaining 231 (25%) seedlings were sells of 'Hass'. Among the 850 seedlings of 'Bacon', 382 (45%) were hybrids with 'Hass' and the remaining 468 (55%) seedlings were sells of 'Bacon'. The high outcrossing rate observed in the 'Hass' seedlings was expected, because adjacent rows of opposite flowering types (A versus B) are expected to outcross. However, the high selfing rate in 'Bacon' was unexpected. A previous study in Florida using the cultivars 'Simmonds' and 'Tonnage' demonstrated differences in outcrossing rates between complementary flowering type cultivars. In both Florida and California, the A type parents ('Hass' and 'Simmonds') had similar outcrossing rates (~75%); however, the B type parents ('Bacon' and 'Tonnage') had highly skewed outcrossing rates of 45% and 96%, respectively. Two new avocado lethal mutants were discovered among the selfed seedlings of 'Hass' and 'Bacon'. These were labeled "spindly" and "gnarly" and are similar in phenotype to mutants described in Arabidopsis and other crop species. [ABSTRACT FROM AUTHOR]

Abstract: A plant–bacterium association between the giant cardon cactus Pachycereus pringlei and endophytic bacteria help seedlings establish and grow on barren rock. This cactus, together with other desert plants, is responsible for weathering ancient lava flows in the Baja California Peninsula of Mexico. When cardon seeds are inoculated with endophytic bacteria, the seedlings grow in pulverized rock for at least a year without fertilization and without showing distress. The bacteria–plant association released significant amounts of necessary nutrients from the substrate. When endophytic bacteria were eliminated from the seeds by antibiotics, development of seedlings stopped. In complementary experiments of sterile seeds inoculated with the same endophytic bacteria, plant growth was restored. This study and the previous one show that, under extreme environmental conditions, a symbiotic relationship is present between endophytic bacteria and their cactus host. [Copyright &y& Elsevier]

Question: We present a study of positive and negative interactions between the invasive grass Schismus barbatus (Poaceae) and Ambrosia dumosa (Asteraceae). Ambrosia facilitates seedling establishment, and such facilitation may accelerate invasion of exotic species, which, in turn, may reduce establishment of native plants. Location: Joshua Tree National Park, California, USA. Methods: During 2003-2004, we used field surveys to characterize the natural spatial distribution of Schismus in relation to native shrubs, and experimentally manipulated seed rain of Ambrosia and Schismus at three distances from adult Ambrosia canopies. We measured percentage germination and individual performance of both species. Field data were complemented by a greenhouse experiment that measured competition between Ambrosia seedlings and Schismus planted at three densities and five relative abundances under controlled conditions. Results: Field surveys showed that the density of Schismus is independent of Ambrosia shrubs, but growth is enhanced near shrub canopies. In our field experiment Schismus is facilitated by adult Ambrosia. Under controlled conditions, Schismus does not respond to the density of Ambrosia seedlings, but changes in density of Schismus decreased performance of Ambrosia seedlings. Conclusion: Schismus invasion may be detrimental to native perennial plant populations. Although a reduction of seedling establishment is not usually expected to slow population growth of long-lived perennials, recent unprecedented adult mortality in this community, and the well-documented facilitative role of Ambrosia, suggest that Schismus invasion may be of high ecological significance. [ABSTRACT FROM AUTHOR]

Some species of animals provide directed dispersal of plant seeds by transporting them nonrandomly to microsites where their chances of producing healthy seedlings are enhanced. We investigated whether this mutualistic interaction occurs between granivorous rodents and Jeffrey pine (Pinus jeffreyi) in the eastern Sierra Nevada by comparing the effectiveness of random abiotic seed dispersal with the dispersal performed by four species of rodents: deer mice (Perornyscus inaniculatus), yellow-pine and long-eared chipmunks (Tamias amoenus and T. quadrimaculatus), and golden-mantled ground squirrels (Spermophilus laleralis). We conducted two caching studies using radio-labeled seeds, the first with individual animals in field enclosures and the second with a community of rodents in open forest. We used artificial caches to compare the fates of seeds placed at the range of microsites and depths used by animals with the fates of seeds dispersed abiotically. Finally, we examined the distribution and survival of naturally establishing seedlings over an eight-year period. Several lines of evidence suggested that this community of rodents provided directed dispersal. Animals preferred to cache seeds in microsites that were favorable for emergence or survival of seedlings and avoided caching in microsites in which seedlings fared worst. Seeds buried at depths typical of animal caches (5-25 mm) produced at least five times more seedlings than did seeds on the forest floor. The four species of rodents differed in the quality of dispersal they provided. Small, shallow caches made by deer mice most resembled seeds dispersed by abiotic processes, whereas many of the large caches made by ground squirrels were buried too deeply for successful emergence of seedlings. Chipmunks made the greatest number of caches within the range of depths and microsites favorable for establishment of pine seedlings. Directed dispersal is an important element of the population dynamics of Jeffrey pine, a dominant tree species in the eastern Sierra Nevada. Quantifying the occurrence and dynamics of directed dispersal in this and other cases will contribute to better understanding of mutualistic coevolution of plants arid animals and to more effective management of ecosystems in which directed dispersal is a keystone process. [ABSTRACT FROM AUTHOR]

Using a historical reconstruction, we discovered a potential trophic cascade involving cougar (Puma concolor), mule deer (Odocoileus hemionus), and California black oak (Quercus kelloggii) in the Yosemite Valley of Yosemite National Park in California. Our objective was to determine whether large deer populations in the absence of a top-level carnivore were suppressing tree regeneration. As human visitation increased in the early 1900s and cougar became increasingly scarce, the mule deer population irrupted in the 1920s. In August 2006, we undertook a retrospective study of black oak recruitment (i.e., growth of seedling/sprouts into tall saplings and trees) by inventorying all black oaks in stands accessible to deer and greater than 0.5ha in size (18 stands, 2921 trees). We similarly inventoried oaks within sites representing refugia from deer browsing (4 stands, 481 trees). While significantly diminished oak recruitment has occurred since the 1920s in stands accessible to deer (p <0.01), continuous recruitment of oaks was found in refugia sites. We also found less oak recruitment in areas of high human activity near the park’s visitor center (p <0.01), possibly due to behaviorally-mediated effects of lower cougar and higher deer densities. Overall our results are consistent with trophic cascade theory involving large predators, herbivores, and plants. The long-term lack of oak recruitment is also an indicator of a probable loss of biodiversity. [Copyright &y& Elsevier]

Low recruitment of new plants as currently observed in several California oak species might partly result from insufficient storage of vital resources (reduced ability to regrow after disturbance) or from low adaptation to environmental stress, such as drought. We conducted two studies under divergent environmental conditions to compare seedlings of California oaks with ecologically equivalent species from the eastern Mediterranean region, where recruitment has been substantial over the past 25–30 years. Resource concentrations (nonstructural carbohydrates and nitrogen) in taproots and the ratio of root resource content to shoot biomass did not provide evidence that Californian oak seedlings have smaller reserves for resprouting than eastern Mediterranean species in these studies. However, we observed lower seedling survival among California species, when compared with Mediterranean species, under conditions of higher drought stress. In the California deciduous Quercus douglasii Hook. & Arn., water-use efficiency as measured by leaf gas exchange and leaf δ13C was lower compared with its Mediterranean equivalent Quercus ithaburensis Decne. In addition, stomatal conductance in the California evergreen Quercus agrifolia Née appeared to be less sensitive to vapor pressure deficit than in its Mediterranean equivalent Quercus calliprinos Webb. Our results suggest lower adaptation to drought in the California species tested here as compared with Mediterranean species, which will negatively impact recruitment of oaks from California under the currently drier soil conditions. Le faible recrutement de nouveaux plants observé actuellement dans le cas de plusieurs espèces californiennes de chênes pourrait en partie être le résultat du stockage insuffisant de ressources vitales (capacité réduite de se remettre à croître après une perturbation) ou d’un manque d’adaptation à un stress environnemental tel que la sécheresse. Nous avons réalisé deux études dans des conditions environnementales divergentes pour comparer les semis des chênes de la Californie avec des espèces écologiquement équivalentes provenant de la région est de la Méditerranée où le recrutement a été important au cours des 25–30 dernières années. La concentration des ressources (hydrates de carbone non structuraux et azote) dans la racine pivotante et le rapport entre le contenu en ressources des racines et la biomasse de la tige n’a pas permis de démontrer que les semis des chênes californiens avaient moins de réserves pour produire des rejets que les espèces de l’est de la Méditerranée que nous avons étudiées. Cependant, nous avons observé un taux de survie plus faible chez les espèces californiennes comparativement aux espèces méditerranéennes dans des conditions de stress hydrique plus intense. Chez Quercus douglasii Hook. & Arn., une espèce californienne décidue, l’efficacité de l’utilisation de l’eau, mesurée par les échanges gazeux foliaires et la valeur de δ13C dans les feuilles, était plus faible comparativement à l’espèce méditerranéenne équivalente Quercus ithaburensis Decne. De plus, la conductance stomatale de Quercus agrifolia Née, une espèce californienne sempervirente, a semblé être moins sensible à un déficit de pression de vapeur que l’espèce méditerranéenne équivalente Quercus calliprinos Webb. Nos résultats indiquent que les espèces californiennes testées ici sont moins bien adaptées que les espèces méditerranéennes, ce qui aura un impact négatif sur le recrutement des chênes de la Californie dans les conditions actuelles caractérisées par un sol plus sec. [ABSTRACT FROM AUTHOR]

Rice seedlings are sensitive to low temperatures (≤15°C) and under prolonged or repeated exposure, yellowing and stunting are commonly observed. Damage to seedlings results in poor stand establishment and delayed maturation, which can cause significant reductions in yield. In general, japonica rice varieties exhibit more cold tolerance than indica varieties. Earlier genetic analysis of the California rice variety M202 revealed several quantitative trait loci (QTL) that contribute to its tolerance to low temperatures in comparison to the indica rice variety IR50. Among these QTL, qCTS4 is associated with tolerance to yellowing and stunting of rice seedlings and accounts for 40% of the phenotypic variation. Here we report on the fine mapping of qCTS4 to a 128 kb region of chromosome 4, which is highly suppressed for recombination in our mapping populations. Our results provide the necessary foundation for identifying the gene(s) underlying qCTS4 and the markers developed here may be used to introgress this region into indica varieties to improve seedling tolerance to low temperatures. [ABSTRACT FROM AUTHOR]

Understanding causal factors of exotic species invasions is important not only for prevention and prioritizing control efforts, but also for providing valuable insights into the underlying biology of contrasting life-history strategies. In seedling growth analyses, invasive woody species were compared with less-invasive woody species commonly cultivated in California using phylogenetically corrected procedures (12 phylogenetically independent contrasts). Invasive species were hypothesized to have higher seedling relative growth rates (RGRs) and specific leaf areas (SLAs) than did related less-invasive species. In phylogenetically independent contrasts conducted among taxa within families, high seedling RGRs and SLAs have significant positive associations with woody plant invasiveness. For contrasts containing species invasive in mediterranean regions, invasive species had significantly larger root biomass allocation than did less-invasive species. Optimization of fast seedling growth (high RGR) associated with opportunistic resource acquisition (high SLA) and increased root allocation to survive summer drought may be critical for the success of plant invaders in regions with mediterranean climates. [ABSTRACT FROM AUTHOR]

Investigations into the causes of variation in native bunchgrass distributions in California are constrained by the rarity of extant populations, their highly invaded nature, and their diverse and often unknown historical backgrounds. In addition, the correlates of success in California grassland restoration projects are rarely monitored. While controlling for seeding densities, we investigated correlates of establishment success for a mix of native bunchgrasses seeded into a non-native annual grassland with a history of agriculture and grazing in Yolo County, California. Six native grass species—blue wildrye (Elymus glaucus), big squirreltail (Elymus multisetus), Idaho fescue (Festuca idahoensis), California melicgrass (Melica californica), purple needlegrass (Nassella pulchra), and Sandberg bluegrass (Poa secunda)—were drill seeded in the fall of 1999. In order to minimize recruitment of non-native annual grass seed, the land was prepared with a spring burn and fall application of glyphosate prior to seeding. Through the third growing season, the cover of planted native grasses was significantly greater on north-facing slopes than on slopes with southern aspects. This was likely due to more mesic conditions on such sites rather than reduced competition with non-native plants. In the first growing season, distinct dense patches of filaree (Erodium botrys) became apparent. Native bunchgrasses overall, non-native grasses, and non-native forbs all had significantly less cover inside these patches of filaree. Purple needlegrass was an exception to both of these trends, being insensitive to both aspect and filaree patches. These results reinforce the reputation of purple needlegrass as a species with wide ecological tolerance and excellent restoration potential. [ABSTRACT FROM AUTHOR]

Extreme events shape population and community trajectories. We report episodic mortality across common species of thousands of long-lived perennials individually tagged and monitored for 20 years in the Colorado Desert of California following severe regional drought. Demographic records from 1984 to 2004 show 15 years of virtual stasis in populations of adult shrubs and cacti, punctuated by a 55–100% die-off of six of the seven most common perennial species. In this episode, adults that experienced reduced growth in a lesser drought during 1984–1989 failed to survive the drought of 2002. The significance of this event is potentially profound because population dynamics of long-lived plants can be far more strongly affected by deaths of adults, which in deserts potentially live for centuries, than by seedling births or deaths. Differential mortality and rates of recovery during and after extreme climatic events quite likely determine the species composition of plant and associated animal communities for at least decades. The die-off recorded in this closely monitored community provides a unique window into the mechanics of this process of species decline and replacement. [ABSTRACT FROM AUTHOR]

In some California locations, the natural regeneration of blue oak is limited by the ability of small seedlings to survive long enough to become larger saplings. This study evaluated the growth and survival of different age classes of seedlings. We found that over a 7-year period, older blue oak seedlings has a much higher survival rate than younger seedlings. Under this study's condition, however, the height of younger seedlings increased while that of older seedlings decreased. These results suggest that once a seedling survives approximately a decade and becomes established, it is much more likely to remain alive compared to newly germinated seedlings. Nonetheless, its height growth rate may be extremely slow. [ABSTRACT FROM AUTHOR]

Blue oak, a tree native only to California, is notoriously slow-growing, and its low regeneration rate has prompted concern about the species' future survival in some areas of the state. We studied the use of fencing (exclosures) to protect seedlings from herbivores and promote faster growth. Placing exclosures 2 and 4 feet in diameter around blue oak seedlings increased their height and canopy area when compared to a control without exclosures. The 4-foot exclosures increased growth (height and canopy area) compared to the 2-foot exclosures. It appeared that exclosures reduced damage from both wild and domestic herbivores, resulting in accelerated growth rates. [ABSTRACT FROM AUTHOR]

Recent evolutionary models of range limits emphasize the importance of ecological and demographic factors operating at species' margins. This study aims to establish the ecological context driving population boundaries in Gilia tricolor, a native California annual restricted to distinct habitat patches in the coastal range of California. A transplant experiment in one hillside G. tricolor population examined the roles of competition and soil chemistry as well as litter and biomass accumulation in setting local population boundaries. Results indicate that boundaries are maintained primarily by inhibition of seedling emergence by vegetation and litter, and that upslope and downslope population boundaries are heterogeneous in litter biomass and transplant performance. Consistent emergence inhibition in undisturbed, peripheral sites maintains limits to the distribution of G. tricolor in this population. Fine-scaled ecological heterogeneity and heterogeneous boundary conditions likely play important roles in limiting adaptation and subsequent range expansion at population boundaries in G. tricolor. [ABSTRACT FROM AUTHOR]

1 Spatiotemporal responses to habitat conditions are important components of plant population and community dynamics. Plant stage or size is a common predictor of plant performance for a range of ecological conditions, including responses to neighbours. Plant response to local conditions varies from seedling establishment through to senescence, with strong implications for population regulation. 2 I investigated size-dependent responses to near adult neighbours among a uniquely quantitative sample of mapped juvenile and adult bur-sage ( Ambrosia dumosa), a common shrub in the Colorado Desert of California. 3 Analyses of juvenile establishment and survival for two 5-year census periods from 1984 to 1989 and 1989 to 1994 determined that germination and survival was greater for juveniles located under adults compared with away from adults. However, analyses of neighbour effects on growth of plants from the 1984 cohort showed that near adult neighbours improved juvenile growth over the 10-year interval from 1984 to 1994, but reduced adult growth. 4 A size-dependent, ontogenetic shift occurs because neighbouring adult plants significantly improve the demographic performance of juveniles, but diminish that of larger established plants. 5 The ontogenetic niche shift may be a useful framework to describe such differential responses of juvenile and adult plants. The utility of this framework is that responses to spatial and temporal variability in the environment are clearly demonstrated through ontogenetic constraints on plant performance, which provide an alternative mechanism of coexistence within and between species. [ABSTRACT FROM AUTHOR]

We review published studies on the demography and recruitment of California oak trees and focus on the widespread dominant species of the foothill woodlands, Quercus douglasii, Q. lobata, and Q. agrifolia, to ascertain the nature and strength of evidence for a decline in populations of these species. The vast majority of studies have been of short duration (less than three years), focused on the acorn and seedling life stages, and conducted at few locations within each species' geographic range. We summarize the extensive body of research that has been conducted on the biological and physical factors that limit natural seedling recruitment of oaks. The oak "regeneration problem" has largely been inferred from current stand structure rather than by demographic analyses, which in part reflects the short-term nature of most oak research. When viewed over longer periods of time using field surveys or historical photos, the evidence for a regeneration problem in foothill oaks is mixed. Q. douglasii shows very limited seedling or sapling recruitment at present, but longer term studies do not suggest a decline in tree density, presumably because rare recruitment is sufficient to offset low rates of mortality of overstory individuals. Q. agrifolia appears to be stable or increasing in some areas, but decreasing in areas recently impacted by the disease Phytophthora ramorum. Evidence from the few available studies is more consistent in suggesting long-term declines in foothill populations of Q. lobata. Longterm monitoring, age structure analysis, and population models are needed to resolve the current uncertainty over the sustainability of oak woodlands in California. [ABSTRACT FROM AUTHOR]

In this study we analyzed the spatial structure of ectomycorrhizal tilngi present in the soils as resistant propagules (e.g. spores or sclerotia) in a mixed-conifier forest in the Sierra Nevada, California. Soils were collected under old-growth Abies spp. stands across approximately 1 km and bioassayed with seedlings of hosts that establish best in stronger light (Pinus jeffreyi) or that are shade-tolerant (Ables concolor). Ectomycorrhizal fungi colonizing the roots were characterized with molecular techniques (ITSRFLP P and DNA sequence analysis). Wilcoxina, five Rhizopogon species and Cenococcum were the most frequent of 17 detected species. No spatial structure was detected in the resistant propagule community as a whole, but P. jeffreyi seedlings had higher species richness and associated with seven Rhizopogon species that were not detected on A. concolor seedlings. We drew two conclusions from comparisons between this study and a prior study of the eclomycorrhizal community on mature trees in the same forest: (i) the resistant propagule community was considerably simpler and more homogeneous than the active resident community across the forest and (ii) Cenococcum and Wilcoxina species are abundant in both communities. [ABSTRACT FROM AUTHOR]

Investigates the effect of propagation techniques on establishment of valley oaks in a simulated restoration setting in the Central Valley of California. Influence of plant stock type and watering regime on the establishment success of valley oak seedlings; Mortality rates for each combination of stock type and watering regime; Effects on plant height of planting age and irrigation regime; Root excavations; Growth rates of larger oak seedlings.

Seed dormancy models suggest that evaluation of environmental conditions should influence the decision to germinate and that waiting for more favourable conditions may increase potential fitness. However, because rapid emergence is often positively correlated with performance and survival, an alternative strategy to accelerate the rate of emergence may increase the potential for site pre-emption. This response is more likely to be found in seasonal environments with greater potential for rapid resource depletion in which early emergence may confer a competitive advantage. The experiments reported here found more rapid emergence in a perennial grass species when it was planted in potentially highly competitive interspecific neighbourhoods. This response suggests an inherent ability in seeds of this species to sense and respond to the competitive nature of the immediate neighbourhood. [ABSTRACT FROM AUTHOR]

Blackbrush (Coleogyne ramosissima Torr. [Rosaceae]) is a major community type throughout the southern Great Basin, Colorado Plateau, and into the deserts of the southwestern US. This species does not readily regenerate following large fire events. At Joshua Tree National Park, we grow blackbrush from seeds for our restoration projects because it binds soil against erosion and provides shelter for understory vegetation, especially native annuals. Blackbrush is a dominant component of the vegetation in the northwestern portion of the park and is important to wildlife. Seeds are subjected to a brief stratification and germinants are planted individually into containers at the cotyledon stage. Seedlings are ready for outplanting in 9 to 12 mo. [ABSTRACT FROM AUTHOR]

The article presents information on Lost Hills, a new female pistachio cultivar released by the California Agricultural Experiment Station in 2005. It states that the original seedling of this cultivar was planted at a research plot offered by Paramount Farming Co. in 1991. The plant flowers early and the nuts are harvested earlier than Kerman.

Describes propagation techniques for the California redbud or Cercis orbiculata Greene of the species Fabaceae, which is a small tree with attractive spring flowers on predominantly leafless stems. Drought tolerance; Collection of the woody legumes after leaf fall during fall and early winter; Opening of pods by hand to remove the seeds; Sowing of seeds; Watering of seedlings.