Invasive species are an increasingly severe conservation problem that can dramatically alter native plant communities. Although ecologists have proposed many mechanisms for the dominance of invasive species, superior competitive ability is one of the longest standing hypotheses. In winter annual plant communities, germination timing affects competition among plants. I hypothesized that grass invasion has changed the costs and benefits of early and late germination, and that species with flexible germination timing would compete better with invasives. Experiments at the Bernard Field Station in Claremont, CA and germinator trials in a controlled environment were used to examine the survivorship and germination rate of three native forbs in the presence or absence of invasive grass competition. Germinator trials revealed that most Clarkia purpurea seeds germinated in fall conditions, though newer seeds had higher proportions germinate under winter conditions. Older seeds had a lower germination success, indicating a potential decrease in seed viability. In the field experiment, November germinants had higher survival rates than October germinants for Amsinckia menziesii and Phacelia distans, and both species had similar numbers of new germinants at each census. Removal of invasive grasses did not significantly affect the survival of either species, though a trend towards increased survivorship was observed in removal plots of November germinants. Taken together, these results show evidence for variation in germination timing and responses to environmental cues among native annual seeds, and also support the idea that germination timing has important consequences for survivorship, and potentially competitive interactions, with invasive grasses.

Efforts to sequester soil carbon (C) should consider soils intrinsically capable at C retention. Of the mineral soil orders, Mollisols have minimum requirements for soil organic C (SOC; over 0.06 %) and basic saturation (over 50 %). In the U.S., grasslands comprise 93% of the vegetation mapped above Mollisols. Soils beneath the southern extent of Sequoia sempervirens (redwood) forests in central California are mapped as Molliols. It widely accepted that redwood forests harbor considerable biomass C, but the extent to which aboveground C is retained in the soil is not well understood. This study aimed to: (i) to gather baseline soils data (bulk density, pH, basic saturation, cation exchange capacity, SOC, total nitrogen, structure, depth) for an iconic and understudied ecosystem, the southern extent of coast redwood forests and to compare said properties to those in adjacent grasslands, (ii) to identify taxonomic classifications of said soils, (iii) to investigate the influence of vegetative gradation on soil properties between these ecosystems using auger sampling, (iv) to compare levels of basic cations between the forest floor and mineral horizons and, (v) to characterize the total C and active C pools within these ecosystems and to explore interpretations of these pools. In sites randomly selected across two regions, Swanton Pacific Ranch (SPR) and Landels-Hill Big Creek Reserve (LHBCR), soil was collected and described in 24 profiles beneath redwoods and compared to 19 profiles in nearby grasslands. Auger samples at fixed depths were collected in a complimentary study from 5 randomized transects that transitioned through mixed-evergreen forest (and across ecotones) between redwoods and coastal grasslands at SPR. Mineral soil samples were analyzed for SOC, permanganate oxidizable C (POXC), C/N ratio, pH, extractable basic cations, and cation exchange capacity. Samples of forest litter were analyzed for basic cation composition. Multivariate regression models of profile data found higher values of pH, C/N, and CEC in redwoods than in grasslands, and lower values of bulk density in redwoods than in grasslands. Redwood soils were conducive to mollic epipedon formation (21 of 24 profiles in the redwoods as Mollisols) and generally had high base levels, for which extractable calcium from the forest floor was the main driver. Along the transects, multivariate regression returned generally consistent and graded patterns for C/N ratios, POXC/SOC ratios, and pH; these variables were generally highest in the redwood forest and decreased sequentially across mixed-evergreen forest and into the grassland Our look at soil C pools focused on the fraction of SOC that was POXC. Observed higher ratios of POXC/SOC in redwoods than in the grasslands at SPR was corroborated by the transect study; at LHBCR, the regression model provided no evidence for a significant difference in POXC/SOC ratios between communities. Differences in POXC fractions across plant communities and localities were postulated as the result (and combination) of contrasting ecologies, and different management strategies and disturbance histories. The data collected in this study does not provide clear mechanisms to explain these discrepancies, and further research is needed; disharmonious interpretations of POXC across the literature suggested that the replacement of operationally defined C fractions with pools tied to a particular stabilization mechanism would provide clearer insights across ecosystems to land managers. Our estimates of SOC in the top 1 m of soil showed redwood soils stored as much or more C than soils in the neighboring grasslands, at SPR, 144 (± 21) and 123 (± 25) tons SOC per ha in the top 1 m of redwoods and grasslands, respectively, and at LHBCR, 221 (± 23) and 126 (± 24) tons SOC per ha in the top 1 m of redwoods and grasslands, respectively. The carbon densities provided in this study can be used as a baseline to measure changes to SOC and POXC pools in response to future activities to sequester C in our study regions and/or to assess losses from recent 2020 wildfires. We are curious to see how the breadth of information gathered in this study can provide refinement for following questions that will hopefully one day, direct considerate and conscientious management in response to the environmental challenges ahead.