Well, I'm no expert, but I recently bought 50 birch dowels to play with, and they were pretty stiff. You can certainly use them for arrows, and most of them will make good ones, but you may need to leave them long to weaken the dynamic spine. Here are the spines I came up with on 50 of them....
68-1 70-1 73-2 75-3 76-2 79-1 81-1 84-1 87-7 90-2 93-4 96-7 98-1 100-5 104-8 108-3 130-1 They are pretty heavy, too. One I weighed (finished arrow, 160 grain point) was 776 grains.
Hope that helps.