Population biology of rare mariposa lilies (Calochortus: Liliaceae) endemic to serpentine soils in southwestern Oregon

Population dynamics, plant communities, and abiotic environments of three narrowly endemic, allopatric mariposa lilies (Calochortus Pursh) are described and compared. All were restricted to ultramafic soils in southwestern Oregon with high concentrations of nickel, zinc, and chromium, and low calcium to magnesium ratios. Soils inhabited by the three species differed significantly (p < 0.0001) in pH and in concentrations of nickel, cadmium, manganese, magnesium, potassium, vanadium, molybdenum, strontium, and phosphorus. During a nine-year demographic study of Calochortus howellii Watson, reproduction, recruitment, and mortality were evaluated, and possible limiting factors and causes of rarity were investigated. Reproduction fluctuates widely from year to year, with bud production correlated with spring (February to May) precipitation (r² = 0.80, n = 9, p = 0.01). Recruitment and mortality were low and episodic, averaging 3.0% and 2.0%, respectively over 7 years. Capsule production averaged 3.8% during 1987 to 1991, declining from 17.8% the previous 4 years. Growth rates, particularly of seedlings, were extremely slow. Using size-classified transition matrices, changes in population structure and stability were assessed. Three methods of classifying data for transition matrix analysis yielded similar results in equilibrium population growth rates; based on all analyses, the study population was stable ([lambda] = 1.0). Taxonomically very distinct, yet only recently discovered, C. umpquaensis Fredricks and C. coxii Godfrey & Callahan are serpentine endemics known from limited distributions. Despite its narrow edaphic restriction, C. umpquaensis occurs locally within a wide range of habitats from meadows to forests. Based on a four-year study of C. umpquaensis, bud production was highest, plants were most dense, and on average were larger in the ecotone habitat. Equilibrium population growth rates were slightly lower in the meadow habitat. Low capsule production and seedset, low recruitment, high mortality, and declining population trends ([lambda] = 0.9) indicate that C. coxii should be carefully monitored. The probability of local extinction of this taxon is high, if the years studied are typical

Putting Youth on the Map: A Pilot Instrument for Assessing Youth Well-Being

Extant measures of adolescent well-being in the United States typically focus on negative indicators of youth outcomes. Indices comprised of such measures paint bleak views of youth and orient action toward the prevention of problems over the promotion of protective factors. Their tendency to focus analyses at a state or county geographic scale produces limited information about localized outcome patterns that could inform policymakers, practitioners and advocacy networks. We discuss the construction of a new geo-referenced index of youth well-being based on positive indicators of youth development. In demonstrating the index for the greater Sacramento, California region of the United States, we find that overall youth well-being falls far short of an optimal outcome, and geographic disparities in well-being appear to exist across school districts at all levels of our analysis. Despite its limitations, the sub-county geographic scale of this index provides needed data to facilitate local and regional interventions