This document outlines research objectives, methods, and ongoing/new projects related to studying multiple element limitation in northern hardwood ecosystems. The research aims to test for co-limitation of nitrogen and phosphorus on aboveground production in young and old northern hardwood stands. Field sites include 11 stands that vary in age, elevation, slope, and parent material. Fertilization treatments include nitrogen, phosphorus, calcium, nitrogen + phosphorus, and an unfertilized control. Ongoing efforts include measuring responses over the first five years, with new projects this season focusing on mycorrhizal associations, sap flow rates, decomposition, carbon stocks, and soil respiration responses to calcium additions.