Riding style will also have something to do with handling sand and roots also.. Also I have found 29er and 26er bike tires handle pretty different.. for Sand I liked a skinnier tire on my 26er and would go fast through it and it would cut through it like a knife. I found the 29er handles sand better with larger volume tires like Alan and Mellow said.
larger volume will make the roots more manageable for sure. I ended up trying others old tires to see what I liked before I bought something, and others I just bought because they looked like something that would work well.
also, make sure you are not over inflating your tires. too much psi and you will bounce off the roots and sink deeper in the sand instead of floating over it.. I run my psi in the low 30's but I am 280 lbs with full gear, lighter people can run lower but not too low...
then you start start getting into tread patterns and rotational weight, tubelss, tubed, tubeless beads, etc.. tires can get pretty complicated...LOL!