Zhang is a research forester whose research focuses on the effect of forest management on long-term stand dynamics. By analyzing newer data with the archived long-term dataset collectively, he found that thinning both ponderosa pine and true fir stands reduced mortality while maintaining stand productivity. Other benefits by treating stand with lower density included significantly reducing hazardous fuels, increasing carbon sequestration, and enhancing health of residual trees and stand resilience to wildfires and biotic disturbances. A similar result was also found with competition control regardless of stand density in ponderosa pine. In addition, He also studied an impact of post-fire management regimes on carbon pools and forest restoration including assessing the rates of ecosystem carbon recovery. These results were extensively cited in the Environmental Assessment Documents in National Forests across northern California and by forest industries in their regional management strategies.