Walkill High School, Orange County. Using an easy-to-make game, teachers will learn ways to introduce the nitrogen cycle to students of all ages and use local data to think about how ecosystem changes affect nitrogen levels and why that is important for animals and plants. Facilitator: Lia Harris, Cary Institute of Ecosystem Studies. Snow date, March 11. To register, visit www.mhtc.dcboces.org and click "online registration." $3.