When does infrastucture become environment?

A thought came to mind while sitting here at the SMEE. One of the presentations was about how to put economic value to the ecosystem,and it got me to start think as to when infrastructure becomes a part of the ecological environment. Many of us who live in cities take for granted the built environment, and make jokes about the prevalence of weeds and pests, as if the are an integral part of the environment, no matter how much we try to 'control' them.

When do we start thinking of bridges and roads as extant parts of a landscape that must be considered when thinking about cost/benefit analyses? Is it because of the up-front costs that have already been spent that makes us unwilling to think of a space without that road? At what point does a road change from a potential connection between point A and point B into an integral and immovable object, unimaginable to have removed as it was unimaginable at one point to have been built? Why is the removal of the road thought of as a 'trade-off' insteas of the road itself being the trade-off, a cost that is constantly being paid?

This is the problem when thinking of evonomic valuation, environmental/ecological services, and cost/benefit analyses: the human environment is automatically given more weight than the non-human environment, since humans know how to value human things, withn a series of feedbacks that help reach a fair market price. Humans produce many valuable non-physical things as well as a myriad of non-valuable physical objects. This isn't the case with the natural environment.

The natural environment produces primarily physical things. Even the non-physical aspects ascribed to the natural environment (existence value, positive mental feelings from nature, etc) are rooted strongly in a physical reality. Furthermore, the importance of many environmental things are considered 'natural' and 'normal' and, therefore, not something for which people should pay. (And if we did pay, to whom would we give the money?) Perversely, too, the fact that a large part of a physical object's value is based on scarcity and demand, which seems to impy that the fewer of the physical object there are, and/or the greater the demand for those objects, the more interest there is in setting up a merket, since greater value is to be had.

In fact, many ecosysten services fall in the box of 'public goods' (water, air), which are not easy to value in traditionl economics. (I would argue that this is because we humans are not good at giving value to things that are 'natural' and 'normal' to us.

So, this brings me back to the question of the post: 'When does infrastucture become environment?' From the perspective that involves humans, it is when it is built, once it is in place, that it becomes a part of the landscape (environmental, social, and cultural). When we discount what appear to be previously paid costs (eg, the building of the road), our calculations of future changes will not aequately take the reality of constantly paid costs into account.