minetest.register_on_generated(function(minp, maxp, seed)

local vm, emin, emax = minetest.get_mapgen_object("voxelmanip")
	local a = VoxelArea:new{MinEdge = emin, MaxEdge = emax}
	local data = vm:get_data()

	for z = minp.z, maxp.z do
		for y = minp.y, maxp.y do
			for x = minp.x, maxp.x do
				local vi = a:index(x, y, z)
				if data[vi] == minetest.get_content_id("default:stone") and math.random(3) == 1 then
					data[vi] = minetest.get_content_id("default:sand")
					minetest.place_schematic_on_vmanip(vm, { x = x - 4, y = y, z = z - 4}, minetest.get_modpath("default").."/schematics/acacia_tree.mts", "random", nil, true)
				end
			end
		end
	end

	vm:set_data(data)
	vm:write_to_map(data)
	vm:update_map()
end
)