But the value of others – such as the wide range of animal species they support and their intrinsic worth to people – is more difficult to quantify. In attempting to do so, economists have conducted surveys to find out how much people would be prepared to pay to protect forests and the animal species they support.
保护森林是理想的起点，这方面每一美元支出可以带来约10美元的回报。森林所提供的一些资源——如木材、柴火和旅游业等——相对容易估值。但其他资源的价值——如它们所支持的多种动物及其对人类的内在价值——很难量化。为了进行量化，经济学家采用了问卷调查的方式研究人们准备出多少钱保护森林及其所支持的动物物种。