Improving the management of Japanese knotweed s.l.: a response to Jones and colleagues

François-Marie Martin,André Evette,Fanny Dommanget

doi:10.3897/neobiota.63.58918

Abstract

In a recent paper, Jones et al. (2020a) claimed that we recommended the use of mowing for the “landscape management of invasive knotweeds” in an article we published earlier this year (i.e. Martin et al. 2020), a recommendation with which they strongly disagreed. Since we never made such a recommendation and since we think that, in order to successfully control invasions by Japanese knotweeds.l.taxa (Reynoutriaspp.; syn.Fallopiaspp.), stakeholders need to acknowledge the general complexity of the management of invasive clonal plants, we would like to (i) clarify the intentions of our initial article and (ii) respectfully discuss some of the statements made by Daniel Jones and his colleagues regarding mowing and knotweed management in general. Although we agree with Jones et al. that some ill-advised management decisions can lead to “cures worse than the disease”, our concern is that the seemingly one-sided argumentation used by these authors may mislead managers into thinking that a unique control option is sufficient to tackle knotweed invasions in every situation or at any given spatial scale, when it is generally admitted that management decisions should account for context-dependency (Wittenberg and Cock 2001; Pyšek and Richardson 2010; Kettenring and Adams 2011).

Highlights

We reported the results of a mesocosm experiment in which we investigated how homogeneous or heterogeneous conditions of light stress and disturbance affected the clonal growth dynamics of Reynoutria japonica Houtt. and “how these responses might be relevant to improve the management of R. japonica by mowing/cutting or by ecological restoration using dense cover of competitive species” (Martin et al 2020)
We showed that partially mowed/cut knotweed stands were able to compensate for the loss of half of their aboveground organs and, that stands should a minima be entirely mowed/cut to be affected by this control method
While the access to quality information regarding the management of knotweeds is often difficult (Robinson et al 2017; Lavoie 2019), we doubt that a debate in the scientific literature, based on unfair criticisms or partial interpretations, will help managers making good management decisions, the nuanced clarifications we tried to bring in the present response

Summary

Introduction

Despite the assertion of Jones et al (2020a), the “landscape management of invasive knotweeds” through mowing or cutting was never recommended in the article of Martin et al (2020). We highlighted that three mowing/cutting events per year was insufficient to kill young regenerating ramets of R. japonica (arising from rhizome fragments weighing approximately 16 g), illustrating the resilience of the plant and the necessity to use more intense control methods to ensure the eradication of newly-established R. japonica individuals (Martin et al 2020).

Results

Conclusion