sourceY > 0) {
sourceY--;
}
// the grass species can change on each decoration pass
GrassSpecies species = GrassSpecies.NORMAL;
final Biome biome = world.getBiome(sourceX, sourceZ);
if (biomesFernDensity.containsKey(biome)) {
double density = biomesFernDensity.get(biome);
if (random.nextFloat() < density) {
species = GrassSpecies.FERN_LIKE;