Table 1 Hierarchy of quality of evidence based on the information provided in the documents

I

Randomized controlled trials of adequate spatial and temporal scale for the study species

II

Controlled trials without randomization with adequate spatial and temporal scale for the study species

III

Comparisons of differences between sites with and without controls with adequate spatial and temporal scale for the study species.

IV

Evidence obtained from multiple time series or from dramatic results in uncontrolled experiments.

V

Opinions of respected authorities based on qualitative field evidence, descriptive studies or reports of expert committees.

VI

Evidence inadequate owing to problems of methodology e.g. sample size, spatial or temporal scale.