Do I need to humidify my MacKenzie & Marr Guitar?

You bet you do - at least in the colder months! Come November the humidity where we live (Eastern Canada) starts to drop and by mid December it can be less than 40%. That means trouble for an acoustic guitar. Wood moves as it takes on and gives off moisture. That movement is across the grain. But bracing strips inside the guitar running at angles to the wood grain of the body constrain any movement of the top and back. In extremely dry conditions, as the wood contracts and begins straining against braces it has nowhere to go and eventually cracks.

This phenomenon is not unique to guitars or other wooden musical instruments. Look at an antique table. You'll likely see one or two cracks running along the length of the top. Either the leg braces or the end caps, both running perpendicular to the grain of the top, have prevented seasonal expansion and contraction and eventually the table split.

Caring for your guitar in winter and keeping it humidified is not difficult. Follow a couple of simple rules and you'll be fine.
1. Always keep the guitar in its case and keep the case closed. Don't leave the guitar on a guitar stand!
2 Humidify the guitar, either by insuring the room where the guitar is stored never drops below 40% or by using a sound hole humidifier. Music stores sell a variety of in-case humidifiers. They're not expensive and can prevent a ton of trouble down the road.