Years ago, a few of my friends and I got together on a Sunday morning to do something 'enviroment-friendly' (as we were studying about the same in school).
Armed with all kinds of tools we set out to plant little saplings in our neighbourhood; not only we did put little cards with our names around the sapling but we religiously took care of them for a few weeks. Having gotten busy with all the usual activities and excuses, it was a delight to see the saplings happily turning into plants with time whenever we (infrequently) checked up.
Today, as I continue to live in the same neighbourhood, it's an explicable feeling to see that same patch and hope that, amongst all the greenery, our saplings from back then have made it!