What's an Ocular Tube?
An Ocular tube is nothing more than a tube you hold up to your eye. It limits the field of view, focusing on a very specific study area. The one pictured is made of PVC, paper clip wire (for the viewing cross-hairs) and white duct tape to hold the wire in place. You could make one with a paper towel roll and rubber bands!
The most common use for an ocular tube is to study the percentage of canopy cover in a given study area. First lay down a Line Transect, then take a one meter stride. Look straight up through the tube, if the cross-hairs land on vegetation, record a "hit" on your data sheet, if not...record a miss. If you were to record 10 such observations with, let's say 6 hits, you'd have observed 60 percent canopy cover in that study area! Simple!
This type of study can be very revealing especially in the study of a riparian area.