The spread and growth of Solidago gigantea (giant goldenrod) under different management regimes

Background/Question/Methods

Solidago gigantea (giant goldenrod), an invasive species from North America, is considered a major threat to central European natural areas. Although several studies have examined various characteristics of this invasion, the population dynamics and spread are not well understood. Additionally, not enough is known about the management efficacy of common techniques, such as mowing and the use of herbicides, for controlling the population growth and spread of S. gigantea. To begin to address these questions, we combined data from experiments on the demography and spread (via seeds and clonally), to investigate the current projected growth as well as growth under various management scenarios. This stage-based matrix model consisted of small, medium and large vegetative shoots as well as flowering adult shoots. Because S. gigantea success is strongly dependent on site quality, we parameterized the model for both dryer and wetter sites. The population growth rates and elasticities were examined. A separate model of spread was parameterized to explore the contributions to spread from wind-dispersal of seeds and clonal growth.

Results/Conclusions

Projected growth rates of S. gigantea were quite high, and management did not reduce these strongly unless control had a very high efficacy. The stable age distributions were different in the two types of populations modeled (wet and dry environments), with almost no small vegetative shoots in the more productive wet environments.  Population growth rates were most responsive to changes in transition rates between flowering shoots and medium vegetative shoots, and between flowering shoots and large vegetative stems. Mechanical control, which is the most typical management, required a nearly 95% stem reduction to halt population growth. The spread model indicated that most local spread occurred via clonal growth, which is consistent with field observations.  It is likely that alternative management practices need to be explored to reduce the spread of this species.