Your local chain saw dealer should be able to advise you on the chain saw that will meet your needs. You may even consider an electic saw if your "forest" is next to a power source and small limbs and saplings are your only concern. Before you select a chain saw — as a minimum — consider horsepower, bar length, chain type, and safety features (which are explained more fully on my Chain Saw FAQ):
• Horsepower: Use a saw with a power head rated at 3.8 cubic inches or less.
• Bar length: Use the shortest bar possible to accomplish your tasks, to reduce the hazards involved. You should be able to perform all your tasks with a bar length between 16 and 18 inches. Stick with the length you are used to.
• Chain types: Learn how to choose the right chains for your saw and how to sharpen and maintain them. This knowledge will improve your productivity and help you avoid wear and tear on your body and the saw.
• Safety features: Become familiar with your chain brake, throttle safety latch and the guard links on the chain (see illustration).
From U.S. Forest Service's: Backyard Woods - Work Safely With a Chainsaw