Ecosystem services are the benefits humans get from nature. They include clean water, fertile soil, pollination, flood control, and climate regulation. The term was popularized in the 1990s to make the value of nature visible in economic terms. Many of these services are free. That does not mean they are worthless.

Services fall into four categories. Provisioning services supply food, timber, and fresh water. Regulating services control climate, disease, and water flow. Cultural services provide recreation, inspiration, and spiritual value. Supporting services, like nutrient cycling and soil formation, underpin the other three.

Assigning dollar values is controversial. A wetland that filters water saves a city the cost of a treatment plant. That is a real, measurable benefit. But a forest's cultural value resists pricing. Critics worry that monetizing nature leads to selling it. Supporters argue that what is not valued gets destroyed. The debate shapes conservation policy worldwide.

Four categories

• Provisioning
• Regulating
• Cultural
• Supporting