Stationary Rope System, also called Single Rope Technique refers to ascending and descending while the rope stays stationary in the system. For this approach, more gear is required but the ascent will be faster. 

Moving Rope System, also called Doubled Rope Technique, refers to a rope system that moves while a climber is also in motion. This approach is generally preferred by beginners because it is safer.  In general, for climbing taller trees with a height of 300 feet or more, SRS is more common. Where, MRS is more fitting for climbing trees up to 100 feet. 

There are pros and cons to both systems, and depending on the nature of the work, and the age and height of the tree, climbers should determine the best technique.