Roles of succession, light, nutrients and disturbance on population vigor and maintenance of the rare plant Solidago shortii (Asteraceae)

Results of field and glasshouse experiments on Solidago shortii, and our ob servations on this species over many years, were used to construct a concep tual model of the roles of succession, light, soil nutrients and disturbanc e on population vigor and maintenance of this federal-endangered species. A s cover of woody vegetation increased at a population site between 1986 and 1992, number of flowering ramets of S. shortii significantly decreased but number of vegetative ramets remained nearly constant. Adult plants transpl anted into a redcedar thicket and those shaded in a glasshouse produced man y fewer flowering ramets and capitula per flowering ramet and less biomass and had higher mortality than those in the open. Seedlings/juveniles shaded in a glasshouse had significantly less dry biomass; lower RGR, NAR, leaf a rea and root/shoot ratio and higher LAR, SLA and LWR than nonshaded ones. I n a field site and glasshouse, fertilized plants (NPK) consistently had mor e flowering ramets and capitula per flowering ramet than nonfertilized ones . Hierarchy of dry weight of plants grown in a glasshouse in soils derived from five types of bedrock was phosphatic limestone > calcareous shale > sa ndstone > black shale = dolomite. Flowering and biomass production in the f ield-fertilizer and soil-type experiments were associated closely with leve ls of P. Number of flowering ramets significantly increased in plants trans ferred from shaded to nonshaded glasshouse conditions, but no such increase occurred after opening the canopy above plants in a thicket. Both high lig ht and high nutrient levels apparently are necessary to maintain high vigor of S. shortii. In areas subject to invasion by woody plants, periodic high intensity disturbance may be required to prevent population extirpation.