Downed wood that you found in the forest is not usually the ideal fuel for immediate use in your wood stove, but it can be used if necessary. If no other fuel source is available, having the ability to heat your home and cook your food with found wood can be a literal lifesaver.
Tools for foraging include a small hand axe for chopping limbs and splitting logs, a sturdy firewood carry bag for carrying your fuel, a wood moisture meter, and a saw capable of cutting through a medium sized log. An electric or gas chainsaw is very helpful, but a 21” or larger bow saw will work if you don’t mind the manual labor, and a human-powered saw may be most reliable in an emergency.
Learn to identify your local trees by their leaves and bark so that you can pick out desirable firewood. Hardwoods like oak and maple are ideal for wood stove fuel. Softwoods have lower BTU content than hardwoods since they’re less dense, but they can also work well as stove fuel. Soft, sappy woods like pine should be avoided if possible, since they can cause excessive creosote formation.
Wood that has been down for a long period of time can still have a surprisingly high moisture content. Look for downed wood that has been sitting for a long while, but isn’t rotten. Bark that is falling off is often a good sign that a piece of wood is worth investigating. Sometimes a good piece of wood is rotten on the outside, but has a core of solid dry wood. Once you think you’ve found a good candidate, cut a log from it, and split the log. Use a moisture meter on the freshly split surface to verify that the moisture content is 20% or lower. If the wood is dry, cut as many logs as you can carry back home.
Avoid using wet fuel if possible, but if you have no other choice, there are a few things you can do to improve your results. Cut your driest fuel into kindling to get your fire going. Wet kindling will require several tries to start a fire. Cut your wet fuel into small pieces to make it easier to drive off the moisture, and put new logs in the fire before you need them, so they have time to dry out. Understand that the heat output of your stove will be significantly reduced with wet fuel, and your chimney will fill with creosote much more quickly. Be sure to inspect your flue system frequently and sweep it as often as necessary to avoid significant creosote buildup.