No abstract

Establishment of persistent plant populations may be restricted by limitations on the numbers of seeds, emergence of seedlings, or survival to reproductive maturity. The relative importance of these phases in establishment of new populations, particularly restorations, is poorly understood. In an experiment to quantify seedling emergence and juvenile survival of Echinacea angustifolia during its reintroduction to previously agricultural sites, we evaluated effects of two types of vegetation and prescribed burning at four times relative to sowing. We collected achenes from prairie remnants in western Minnesota, United States, and, each October 2000-2002, overseeded them into nearby study plots either in recently planted stands of native grasses or in oldfields abandoned 40 years earlier. For each cohort, we determined germinability of achenes in the laboratory and, in the field, monitored seedling emergence the following spring and subsequent survival in annual censuses through summer 2009. Germinability ranged from 20 to 37%, varying significantly among collection years. Seedlings emerged in every treatment combination, but emergence rarely exceeded 8% of achenes sown. Burns during the spring prior to sowing tended to enhance emergence, but to differing degrees depending on the year and vegetation. Burning in the spring after sowing reduced emergence. Burning enhanced juvenile survival in restored plots but not in oldfields. Strategies to reintroduce this species should include burning in the spring before sowing, sowing large quantities of seed, avoiding burning in the spring following sowing, and burning at least once within the first 6 years.

Allocation trade-offs are predicted to affect evolutionary dynamics, including the evolution of sexual dimorphism. In gynodioecious species, where populations have both females and hermaphrodites, selection may result in sexual dimorphism in individual traits or trait correlations because, in contrast to females, hermaphrodites acquire fitness through both male and female function. Using the gynodioecious species Silerie vul^aris, we measured reproductive traits (ovule number, ovule size, anther size, and floral traits related to display) and a vegetative trait (intemode length) among plants growing under full sun and foliar shade treatments. We tested for sex-specific correlation structures as ' I well as trait plasticity and the sensitivity of correlation structures to the light environment. Hermaphrodites exhibited ' I a fixed trade-off between anther size and ovule size, whereas females exhibited an ovule siz^number trade-off, l-or a I few traits, we detected plasticity to light treatment and plasticity that differed significantly between sexes across light j, treatments. Fxposure ro foliar shade resulted in a sex-specific trade-off between vegetative and reproductive allegation; hermaphrodites exhibited a negative correlation (trade-off) between intemode elongation and ovule number, whereas females showed a marginally significant, positive correlation between these two traits. The tradeoffs observed in hermaphrodites are of particular evolutionary relevance, suggesting that hermaphrodites will evolve to Income increasingly male and populations increasingly sexually dimorphic.