Each PROBE installation is approximately 1.6 ha in size, and consists of a treatment plot (treated operationally with the rest of the opening) and a control plot (area left untreated in the same opening) that have similar site history and ecosystem characteristics. Thirty-six crop tree-centred subplots are established on a grid within each of the treatment and control plots, within which conifer crop tree size, condition, damage, and degree of overtopping are assessed. For each dominant plant species and vegetation group (total vegetation, herbs, shrubs, and broadleaf trees), modal height and cover are also assessed within the 10 or 20 m2 subplots. These measurements are taken prior to brushing and 1, 3, 5, and 10 years after treatment.
Statistical analysis is carried out when a particular treatment cell (i.e., a particular combination of vegetation complex/conifer species/ecosystem/brushing treatment) has been replicated at least three times. Analysis of variance (ANOVA) is conducted separately for each measurement year for quantitative crop tree and vegetation variables, and summary statistics were produced for qualitative variables.
A comprehensive description PROBE methodology is provided in Section 3 of the linked document Effects of Operational Brushing on Conifers and Plant Communities in the Southern interior of British Columbia: Results from PROBE 1991-2000 .