I am retired from USFS. From my recollection, USFS leads the main national forest inventory in cooperation with state forestry, forest industry, other land management agencies, etc.  Long term plots are sampled and evaluated by FIA inventory, including national, state and private industry forest lands.  Beyond that, landowners and managers including urban areas may conduct inventories to suit there own needs.  Most of these inventories are not published, but may or may not be available.  Most inventories are designed to address forests or forest stands, as opposed to individual trees.  As needed, individual trees may get attention on an as needed basis, as appropriate in sampling of plots, and to some degree based on importance to landowner or public, in response to storm, fire or other damage, or in response to management plans.  I believe some of these data are applied to your questions on employment and carbon in various reports from managers, researchers and others.  

I am retired from USFS. From my recollection, USFS leads the main national forest inventory in cooperation with state forestry, forest industry, other land management agencies, etc.  Long term plots are sampled and evaluated by FIA inventory, including national, state and private industry forest lands.  Beyond that, landowners and managers including urban areas may conduct inventories to suit there own needs.  Most of these inventories are not published, but may or may not be available.  Most inventories are designed to address forests or forest stands, as opposed to individual trees.  As needed, individual trees may get attention on an as needed basis, as appropriate in sampling of plots, and to some degree based on importance to landowner or public, in response to storm, fire or other damage, or in response to management plans.  I believe some of these data are applied to your questions on employment and carbon in various reports from managers, researchers and others.  

Dear Rajeev

Good issue to be deliberate upon. To begin with, this should start with TOF. Though it will be a herculean task. i am not aware about the GIS and RS use for individual tree. If it is, then probably, sampling strategy could be effectively designed leading to estimate of the tree. The data generated through this will provide precise estimate of carbon (as specific constants such as C%, SG, Biomass equation). More to that, since different tree species are providing different services specific to the household or adjoining communities, the estimation will further enhance the actual dependency of the households to the tree species. 

In the United States, the national inventory is conducted by the USDA, Forest Service, Forest Inventory & Analysis (FIA) program.  Recently, the FIA has expanded beyond forested areas to also include sampling of urban forests and trees.  

You can take it as forest is not only the collection of trees.

Yes, integrating Trees Outside Forests is of increasing interest for NFIs. Why not read up on that topic more via this thesis?:

http://pub.epsilon.slu.se/12011/

Trees constitute clusters and a group of clusters formulate a forest. You should consider the forest as a living organism (habitat of flora and fauna, soil, air, water resources etc.) and not just as a site full of trees. In many countries Forest/forestlands , according to the current law, may also include areas with low vegetation (grasslands and bushy reagions of special environmental and protective interest). I mean it is much more complicated than it seems.

On the other hand it is possible that the potential biomass arising from an artificial  plantation, for instance, a short rotation forestry cultivation (poplars, eucalyptus etc.) could also be exploited efficiently. But keep in mind that this is mainly a cultivation of trees and not a forest or not even reforestation . Forest management is much more complicated and has to take into account uncountable factors apart from the biomass production and the economic issue.

I hope I have helped you to clarify it a little bit .