Quantifying Plant and Plant Colony Health

Greetings! We are monitoring several indigenous colonies of Ram’s Head Lady’ Slipper orchids. Our measures are plant height, length of lowest leaf, width of lowest leaf, number of leaves, and presence of a flower. My question is this: Using these measures (or other measures), how can we quantify the “health” of each plant, and the “health” of a colony of plants? If there are generally-accepted methods of quantifying plant/colony “health” using other measures, we would also appreciate hearing about such measures. Thanks!