Forest resource use efficiencies vary with tree age, affecting how forests use light and water. Evergreen forests increase efficiency until around 90 years old, then decline, while deciduous forests keep improving as they age. Canopy photosynthetic capacity drives these changes, with mature deciduous forests benefiting from increasing soil nitrogen over time. Soil nutrient conditions play a bigger role in deciduous forests' efficiency compared to evergreen forests. Stand age and forest type are crucial factors in determining how efficiently temperate forests use resources in the long term.