I want to model the aesthetic value of a forest as an objective in an optimization/ mathematical programming problem. The objective may be assessed as a (direct or proxy) indicator based on particular characteristics of the forest.
Ricardo, what about using some evidence from existing works on environmental valuation of landscape/aesthetic values of forests? Some of these studies show for example that mixed stands with mature trees and good visibility hold higher values for society. Then you may use some proxies based on these evidences to build your models.
Some papers on landscape economic valuation that come to my mind and may result useful to build some proxies based on them:
Atauri et al. 2010 Visitors' landscape preferences as a tool for management of recreational use in natural areas. Landscape research 25 (1): 49-62
Tagliafierro, C., et al., Landscape economic valuation by integrating landscape ecology into landscape economics. Environ. Sci. Policy (2013), http://dx.doi.org/10.1016/j.envsci.2012.12.001
1) Edwards et al., 2010. Public preferences for silvicultural attributes of European forests.
2) Edwards et al., 2011. A theoretical framework to assess the impacts of forest management on the recreational value of European forests.
I think for you may be especially interesting the first one, where the influence of different silvicultural attributes on the recreational value of forest stands is analyzed.