A little time goes an even longer way than money. If you want to make sure that your favorite trails and riding areas stay open, donate your time or even better round up a group of your ATV riding friends and make a contribution to a volunteer clean up project or trail maintenance.
Most ATV riders are responsible people who aspire to leave the ATV trails better than they found them. There are a select number however, who with their actions ruin trails, destroy stream crossings, leave litter and do other damage to the trail systems. A good way you can help is to join the Adopt-a-Trail program which is usually coordinated through the Parks and Recreation Department of your State. If you don't have an active adopt a trail program in your area, be a trend setter and start one!
When you adopt a trail, you and/or your ATV group will be giving your word that you will help in creating new trails, relocating bad trails, repairing erosion damage to overused trails, or just trimming brush in spring. You may also find yourself doing a lot of humble trash clean up from folks who just don't understand the forest floor isn't a garbage receptacle.
You can further help by organizing safety seminars to educate ATVers in the ways of proper trail etiquette and you can further implement the teachings of Treadlightly.org and teach more ATVers how to ride environmentally friendly.