 The study shows that including nitrogen and phosphorus cycling in Earth's system model simulations reduces carbon uptake from reforestation and carbon emissions from deforestation, highlighting the importance of considering nutrient-carbon interaction in estimating carbon benefits and losses. Protecting existing subtropical and tropical forests is more effective for climate mitigation than planting new forests in temperate and boreal regions. This article was authored by Yingping Wang, Chen Zhong, Andrew J. Pittman, and others.