Simplify the following text for a Grade 9 native English-speaking person.
Original: The simplest form of ecosystem valuation for economists is to hold that an ecosystem has a value equivalent to its ecological yield valued as it would be on commodity markets : for the value of water , wood , fish or game , that is purified or nurseried or generated or harboured in that ecosystem .
Simplified: The simplest form of ecosystem valuation is that one looks at an ecosystem as if its ecological yield had the same value as it would be on commodity markets . That means one looks at the value of water , wood , fish or game , that is produced in that ecosystem .