Wyethia mollis

Abstract: -A 1977 wildfire destroyed a Pinus jeffreyi forest on the east slope of the northern Sierra Nevada. The area was replanted with 1-yr seedlings of P. jeffreyi. Survival and growth of P. jeffreyi seedlings were determined after 5 and 8 yr in patches dominated by either an herbaceous perennial, Wyethia mollis, or by montane chaparral. Pines in Wyethia plots had 50% greater mortality and 25-33% less annual growth compared to chaparral plots. Pine height growth negatively correlated with percentage cover of Wyethia. Hypotheses are discussed to explain how an herbaceous perennial could prevent forest succession in this semiarid coniferous habitat.

Abstract: Thinnings using cut-to-length and whole-tree harvesting systems followed by prescribed underburning were assessed for their effects on shrub, forb, and grass understory species in a second-growth Jeffrey pine (Pinus jeffreyi Grev. & Balf.) stand. Prior to treatment installation, a mixed shrub-dominated understory featuring antelope bitterbrush (Purshia tridentata [Pursh] DC.) with mules ears (Wyethia mollis A. Gray) as the only forb and Sandberg bluegrass (Poa secunda J. Presl) the most prominent among sparse grasses was inventoried such that both percent cover and dry weight by species were revealed. Five growing seasons after thinning and four after underburning, this inventory was repeated. By either abundance measure, bitterbrush was reduced by approximately two-thirds in the cut-to-length treatment and by one-half in the whole-tree treatment in comparison to that in the unthinned control at the final inventory. For the cut-to-length treatment, a similar reduction in mules ears was noted, but that in ...

Abstract: Regeneration of Pinus jeffreyi in the Sierra Nevada is often limited on sites dominated by Wyethia mollis . Allelopathic chemicals and competition for soil moisture have been suggested as possible mechanisms for limiting regeneration. We tested the hypothesis that soil chemical and microbial properties from sites in different stages of succession influence seedling growth of Pinus jeffreyi . Soil was collected from an early-seral site dominated by Wyethia mollis , a mid-seral site dominated by the shrubs Arctostaphylos patula, Ceanothus prostratus, C. velutinus , and Purshia tridentata , and a late-seral site dominated by mature Pinus . These sites were compared for nutrient content, Pinus seedling growth capacity, and microbial population size. Soil (0-33 cm) from the early-seral site had the lowest C, microbial biomass, and fungal and bacterial populations. There were no consistent trends in soil nutrient content among sites. The early-seral site had the lowest soil Ca and Mg contents but also had a lower C/N ratio and more than twofold greater P content than either the mid- or late-seral site. Pinus seedling growth and foliar nutrient concentrations were compared at 3 harvest dates (220, 314, and 417 days after germination) in a greenhouse bioassay. The treatment design was a 3 × 2 factorial with soil from each of the 3 sites either with or without Pinus seedlings. Pots without seedlings were used as controls to assess the effects of seedlings on microbial biomass. Seedling growth in the early-seral soil was initially suppressed in comparison to growth in the mid-seral soil, but by the final harvest total seedling weight was similar between these 2 treatments. The most obvious treatment effect was a reduction in growth for seedlings planted in lateseral soil, probably due to a nutrient imbalance in the soil. Seedlings grown in late-seral soil had Fe and Al levels that were nearly twice those of seedlings grown in early- and mid-seral soils. Microbial biomass followed a temporal pattern similar to that found for seedling growth. Differences in microbial biomass between the early- and mid-seral soils, although initially large, were not detected by the final harvest. We interpret these results to indicate that allelopathy or soil nutrient deficiencies resulting from the presence of Wyethia are unlikely to be responsible for limited growth of Pinus seedlings in Wyethia -dominated stands.