Table 5 Potential effect modifiers/reasons for heterogeneity

Study in greenhouse/field

Studies of management interventions such as herbicides in greenhouses may be more effective than those in the field because of the lack of exposure to wind/rain that may remove herbicide from target plants

Sub-group analysis

Rate of application of herbicide/cutting (management intensity)

Higher application rate of herbicide may lead to more effective control of invasive plant species

Sub-group analysis/meta-regression

Type/mechanism of herbicide

Different types of herbicide may differ in their effectiveness in controlling target invasive plant species

Sub-group analysis

Timing of herbicide application

Timing of herbicide application may alter their effectiveness in controlling target invasive plant species

Sub-group analysis/meta-regression

Frequency of management intervention (e.g. repeated spraying with herbicide)

More frequent application of herbicide or more regular cutting may lead to more effective control of invasive plant species

Sub-group analysis/meta-regression

Experimental vs observational

The results of experimental studies may be more consistent due to having fewer confounding factors

Sub-group analysis

Time since management intervention

Some management interventions may decline in success as time since they were last carried out increases

Meta-regression

Time since invasion

In sites where invasive plant species have been present for long periods of time they may be difficult to control because of a build-up of invasive propagules

Meta-regression