//---------------------------------------------------------------------------------------------------
//EXTRACT AND EXPORT UNFORESTED AREAS
//---------------------------------------------------------------------------------------------------
//This part is the first step for isolating world alpine areas. The output here is a vector file
//of unforested areas in mountain ranges.

//1. Load GMBA mountain polygons (Koerner et al., 2017) containing at least an alpine
//(according to Koerner et al., 2011), clipped to the extent of their upper montane climatic belt.
var mountainRanges = ee.FeatureCollection('/yourFC');

//2. Create mask of forest extent for the year 2015
//load Hansen's forest cover dataset
var hansenImage = ee.Image('UMD/hansen/global_forest_change_2015_v1_3');
//select forest cover for the year 2000
var forest2000 = hansenImage.select(['treecover2000']);
//select forest losses and gains
var loss = hansenImage.select(['loss']);
var gain = hansenImage.select(['gain']);
//extract forest baseline, add gains, subtract losses
var forestCalc = forest2000.eq(0).not().add(gain.eq(1)).subtract(loss.eq(1));
//build forest extent for the year 2015
var forestExtent = forestCalc.expression('b(0) > 0');
//create mask of unforested areas
var unforestedMask = forestExtent.gt(0);

//3. Clean mask.
//smooth the image by convolving with the boxcar kernel.
var boxcar = ee.Kernel.square({
  radius: 5, units: 'pixels', normalize: true
});
var smoothUnforestedMask = unforestedMask.convolve(boxcar);
//define smoothed alpine mask by setting threshold >0.50
var smoothUnforested = smoothUnforestedMask.gt(0.50);
//reduce ImageCollection to Image with value 1 where it was non zero
var unforestedAreas =  smoothUnforested.reduce(ee.Reducer.allNonZero());
//selected only areas with value 0 (unforested)
var unforestedAreas = unforestedAreas.eq(0);

//4. Vectorize unofrested areas mask, reducing spatial resolution to 50 m, select only unofrested part
//and export to google drive
//convert to vectors.
var unforestedVectors = unforestedAreas.addBands(unforestedAreas).reduceToVectors({
  geometry: mountainRanges,
  crs: unforestedAreas.projection(),
  scale: 50,
  geometryType: 'polygon',
  eightConnected: false,
  labelProperty: 'zone',
  maxPixels: 1e13,
  reducer: ee.Reducer.mean()
});
//select alpine polygons ("zone" = 1)
var unforestedVectors = unforestedVectors.filter(ee.Filter.eq('zone',1));

//export the FeatureCollection to a SHP file.
Export.table.toDrive({
  collection: unforestedVectors,
  folder: 'bioclimatic/3_forestBorder',
  description:'forestBorder',
  fileFormat: 'SHP'
});