Nutrient availability in soil affects how ecosystems respond to global changes. Scientists reviewed different ways to compare soil nutrient levels across different areas. They found that using soil-based metrics is the best way to compare nutrient status between forests. Plant-based metrics are limited because they depend on the type of plant species present. By focusing on soil metrics like organic carbon concentration and C:N ratio, researchers can better understand and compare nutrient levels in forests dominated by spruce, pine, or beech trees. Gathering consistent soil data from various sites is crucial for refining these metrics in the future.