Load libraries and grab tree cover data: https://catalog.data.gov/dataset/nlcd-2011-percent-tree-canopy-cartographic

Tree canopy cover ranges from 0-100%.

library(rgdal)
## Warning: package 'rgdal' was built under R version 3.3.2
## Loading required package: sp
## Warning: package 'sp' was built under R version 3.3.2
## rgdal: version: 1.2-5, (SVN revision 648)
##  Geospatial Data Abstraction Library extensions to R successfully loaded
##  Loaded GDAL runtime: GDAL 2.1.2, released 2016/10/24
##  Path to GDAL shared files: /Library/Frameworks/R.framework/Versions/3.3/Resources/library/rgdal/gdal
##  Loaded PROJ.4 runtime: Rel. 4.9.1, 04 March 2015, [PJ_VERSION: 491]
##  Path to PROJ.4 shared files: /Library/Frameworks/R.framework/Versions/3.3/Resources/library/rgdal/proj
##  Linking to sp version: 1.2-4
library(raster)

x<-raster("nlcd_2011_USFS_tree_canopy_2011_edition_2014_03_31/cartographic_product/nlcd2011_usfs_treecanopy_cartographic_3-31-2014.img")
plot(x)