Bring some tree seeds (native to your locale or at least country) along on long rides, and do some Johnny Appleseed. Plant a tree(s) every x-miles you ride. With all the Epic Ride Reports I see, there seem to be a lot of members traveling to a lot of different places, some very remote, some bordering high polluting cities, and some probably suffering from deforestation. I'm not an arborist, so I'm not sure exactly what the offset would be but it couldn't hurt, and the seeds shouldn't add much to your pack size at all. Short rides, less luggage space, less miles traveled all means less trees. Longer rides, more luggage space, log more miles and plant more seeds.