Note that the analysis presented here re- lates to a single site. As discussed above, however, the value of any single site de- pends upon the extent to which it is unique. As the total amount of tropical forest is re- duced through deforestation, one can ex- pect that the remaining sites are going to increase in value because they will become more unique as substitute sites are de- stroyed. In Costa Rica, there is evidence that tourism to specific tropical forests is increasing over time (6); this is certainly true at Monteverde. Equation 4 would un- derestimate the total benefits in this case. For example, if tourism in-creased at a rate of "a" percent a year, the present value of this increasing stream