Quantifying population growth rates of an invasive weed: responses to soil fertility and cattle management

Abstract

Sericea (Lespedeza cuneata) is an invasive, perennial legume that suppresses native plant species and threatens native grasslands in the Great Plains. Although much is known about Sericea, population demographics (survival, growth, reproduction, and population growth rates) have never been assessed over realistic temporal and spatial scales. For two growing seasons, we quantified Sericea vital rates across eight, large-scale ranching operations representing four cattle management regimes and three soil fertility types. Though soil fertility had no effect on Sericea vital rates, seedling survivorship was significantly higher in pastures with stocker than cow-calf cattle. Survivorship was lower among juvenile (~ 69%) relative to mature plants (~ 93%). All plant stages exposed to herbicide experienced a 67% reduction in survivorship on average. Reproduction was variable but high and on average comprised of 25 chasmogamous (outcrosspollinated) and 235 cleistogamous (self-pollinated) seeds/stem. The proportion of chasmogamous seeds produced/plant increased with increasing soil fertility. Preliminary models revealed a population growth rate (λ) of 2.3, suggesting a rapidly growing population. Given low juvenile survivorship, preliminary results suggest control efforts focus on mature plants regardless of soil fertility type or cattle management. However, these responses need to be verified over additional years to better predict bioeconomic impacts and guide weed management decisions.