Less permanent raised beds

Hello, I'm wondering if anyone knows how many seasons I can expect a raised bed to hold together if I use non-cedar wood.  We have a variety of maples, a little oak and lots of unidentified deciduous trees in our wood.  No conifers or cedar.  My goal is to slowly work an entire 1/2 acre into a heavily mulched bed that I can rotate through freely with annuals. Until that happy day though I need to add some raised beds for more delicate annuals- herbs and things that don't grow well in alkaline soil (we're at 7.8 here).  I'm hoping to install a few beds and plant some things straight into our ground while also mulching very heavily on paths and any unused beds.  Hopefully in 5 years or so the whole thing will have enough organic matter for flood/drought control and easier weed control that I can simply remove any leftover bed edges and have a blank canvas.  

If you can make your beds from maple or oak logs (say 8-12" diameter), I'm guessing that they will hold in soil for at least 5 years.  When they get too rotten maybe they'll just become part of the next garden.

I second Mikes guess that laying 8-12" logs on the ground may get you five years. Mushroom spores with quickly spawn on those logs and the fungi will start their job. Termites may likely find the logs since they will be in contact with the earth. Other bugs will make a home in them. And a cool bonus thing here, when they start totally falling apart and you plan to remove them anyway, they will simply be more organic matter to use in soil in the next project.

Thank you both, that sounds perfect! I'm far from a perfectionist when it comes to neatness so this sounds like a great plan.

While I was living in a rented duplex in Charleston, South Carolina I got permission from the landlord to build two raised beds. I constructed both from 2x6 untreated pine. When I moved out three years later, both were still structurally sound.