Keeping a cane chair in an overly dry, hot environment can cause the cane to dry out, making it brittle and prone to breakage. Storing the chair near a heater indoors can also cause drying issues and brittleness. Over time, these conditions hastens the aging process of the cane, which is essentially a dead vine. Like other dead organic material kept in overly dry environments, as the cane ages it will dry out even more.
Aside from keeping your chair away from heaters and extremely dry conditions, there are other things you can do to prevent the chair's premature aging and brittleness. Keep it out of direct sunlight -- don't use it outdoors on a patio where the sun will beat down on it day after day. Spritz a little water on the chair from time to time with a spray bottle to reintroduce moisture back into the dry cane. A water spritz on a sagging cane seat will help the cane tighten back up as it dries too, taking some of the sag out of the chair.
Using or storing a cane chair in an overly damp environment isn't good for the chair either. Excess moisture can cause mildew or mold which can be hard to remove from the chair without bleach, which can alter the color of the chair in some places, leaving it with a mottled appearance. Too much moisture, then extreme drying, can cause the chair to become brittle. If your chair gets extremely wet, wipe it down with a towel. A little moisture is good for the chair, but too much is problematic.
To keep your chair in good usable condition for as many years as possible, keep it in a moderate climate, such as the inside of your home, out of direct sunlight. Don't leave it out on a porch -- even a screened-in porch -- over the winter in cold climates. Don't leave it somewhere where rain will affect it either. Treat it like a piece of indoor furniture. Continual weather changes will hasten the aging and drying out of the cane, causing it to eventually split, crack or break. Keep it away from temperature and moisture extremes and it will last a lot longer. Wipe it down with a clean cloth once in a while as well. A gentle furniture polish is also acceptable and will help keep moisture within the cane.