NLCD percent tree canopy is a 30 m raster geospatial dataset covering the conterminous United States, coastal Alaska, Hawaii, and Puerto Rico. These data contain percent tree canopy estimates, as a continuous variable, for each pixel across all land covers and types and are generated by the United States Forest Service. The USFS derives canopy cover from both the spectral information in Landsat imagery, and other available ground and ancillary information.  2016 Forest canopy products will be coming soon.

For additional information regarding creation of NLCD percent tree canopy products:

Coulston, J. W., Jacobs, D. M., King, C. R., and Elmore, I. C. 2013. The influence of multi-season imagery on models of canopy cover: a case study. Photogrammetric Engineering & Remote Sensing79(5):469-477. 

Coulston, J. W., Moisen, G. G., Wilson, B. T., Finco, M. V., Cohen, W. B., and Brewer, C. K. 2012. Modeling percent tree canopy cover: a pilot study. Photogrammetric Engineering & Remote Sensing78(7): 715-727.