Here is what I try to do in managing my poplar stands that might be applicable to your pine stands. Your pine stands apparently took 7 to years to go from planting size to too tall for bedding size. That is probably about right for my poplar stands, in fact they may take even less time to go thru the cycle. I like to divide the stand up into six or so pieces in my mind and hinge cut one of those pieces each year with maybe 1/2 of the stems left. How many to leave is a guess for me on the poplar. If it borders open ground then a 1/8 acre cut bounces back pretty quickly like by year two or three; If it is surrounded by woods then an acre cut at once is better to get ample sunlight to the ground. The poplar cutting payback is not just bedding but also browse from cut trees as well as poplar shoots that come up the next spring.
Once the amount is decided then the shape comes into play and as Okie said having as much edge as possible is good. Possible is determined by the amount of sun it will get;for example a strip 1 mile long and ten feet wide (very roughly 1 1/4 acres) would give lot's of edge but not enough sun light. Thus the correct amount of edge lies some where between a square or circle shape and a long and skinny,winding shape. Shape can also come into play regarding the travel patterns it will create. For example two cut areas 100 yards apart would likely have deer moving between them as well as back and forth to them (Your entry and exit of course comes into play here).
Location of the cut comes in regarding where do you want the deer to move to there and from there. For example on the border of your property against a neighbors food plot would make for some great shooting FROM THE NEIGHBORING LAND.In cutting poplar I am pretty certain that poplar will be the main plant sprouting whereas in cutting planted pines I'm guessing that what will come up will depend on the location being cut so some locations might be better choices than others due to that. Sun orientation of course could change location as well, ie; north slope versus south slope.
These are just some of the things I consider when attempting to create bedding areas. It is by no means a complete list of things to consider but rather just a start. And the reason I say "try" to create bedding areas by doing some each year is that some years the winter weather which makes sense to cut then for here is too tough, or I don't fit it into my schedule for whatever reason.
