Several years ago, I purchased a big cardboard tree with leaves from Holcomb's. I hung the tree in the hallway at our school by the office, and I called it The Volunteer Tree. Every time a volunteer spent time helping our school, they got their names put on a leaf, and we hung their leaf on the tree. By the end of the year, the tree was filled with leaves. It was really fun to do, and the volunteers and their children loved to see their names written on the leaves.
I just wanted to quickly chime in here. I think having an end date associated with this will work better. If there is no sense of when the contest ends, it may not be as effective in increasing volunteer hours. Kind of a silly comment I know but I throw contests and when I let everyone know clearly when it ends, the results improve.
Also, these types of improvements take time and the one thing you can do is be consistent. If volunteers are what you want to encourage most, then roll out of this activity into another volunteer building activity so things don't drop off right after the giving tree loses it's luster.
I have seen waterproof printer paper is the office supply store. You cut out leaf shapes but you'd have to test the printer ink on it. Otherwise you could use permanent marker.
Would caution you to think about the "moving up on the tree" part of the idea. Your idea of recognizing people is great but you don't want to guilt people into volunteering, or worse turn them off from volunteering because they work full-time and think that only doing a few hours is too little.
We are deperately trying to get more volunteers into the school as well as trying to get the neighbourhood spirit back!
We have an idea of promoting The Giving Tree, we love the book and think it would be a great way for volunteers to give!
We have a great tree in our courtyard which we intend to make as our giving tree. For every hour our volunteer "gives" to the school then they would somehow move up the Giving Tree. Once they have reached a certain number of hours we will give them a copy of The Giving Tree. We think that if we have something that everyone on campus will see and children will love to watch grow it will improve volunteer participation as well as gain school spirit.
Any ideas on what we can use as emblems on the tree, we thought of large christmas baubles, or apples. We would really like something with the volunteers names/photos on and something that would be weatherproof. We are located in Florida so the humidity and hurricanes could be a problem.