The more we do, the less we gain? Balancing effort and efficacy in managing the Solidago gigantea invasion

Developing invasive plant management strategies is an important task in modern ecology, conservation biology and land management. Solidago gigantea is considered a problematic invader in Europe and Asia, where it forms dominant stands that can decrease species diversity. There is, therefore, an urgent need for effective management to reduce S. gigantea infestations and their negative impacts. We examined the efficacy of multiple approaches to S. gigantea management in Hungary. In our study, we evaluated the effect of several long-term management techniques such as grazing, mowing and periodic flooding on the invader's density as well as native community diversity. In addition, we investigated the short- and long-term effects of mowing combined with other treatment options, to estimate the influence of increased management intensity. Our results indicate that all tested management techniques had negative impacts on S. gigantea density. Short-term mowing did not appear to improve species diversity in the resident community; however, all long-term options improved species diversity. Moreover, combining treatments with mowing varied in its effectiveness; mowing once increased the efficacy of flooding, but decreased the efficacy of grazing, while mowing twice decreased efficacy of flooding. We suspect this is due to the increased intensity of disturbance, which does not allow for the natural recovery of communities, and after management ceases, invasion is able to re-occur. Our results indicate that for effective management, we need to combine management options which act via different mechanisms, leading to cumulative positive effects on the resident community when applied at moderate levels.