The Silky company makes a series of folding Japanese saws with blades up to 1 meter in length. The one I carry in my pack is their Gomboy 310 with a 310mm blade which, with some effort, can handle trees up to about 16 inches in diameter. I seldom come across deadfall any bigger than that in my neck of the woods. There's the very rare 3 foot diameter Douglas Fir that falls across the trail, but at that point it's usually easier to reroute the trail if there isn't a land manager who can send out a crew with chain saws.
Brent