Wood

local function checkFuel()
  if turtle.getFuelLevel() < 20 then
    turtle.select(1)
    turtle.refuel(1)
  end
end

local function column()
  while turtle.digUp() do
    turtle.dig()
    checkFuel()
    turtle.up()
  end
  turtle.dig()

  checkFuel()
  while turtle.down() do
    checkFuel()
  end
end

local function digmove()
  checkFuel()
  turtle.dig()
  turtle.forward()
end

local function fell()
  digmove()
  column()
  turtle.turnRight()
  digmove()
  turtle.turnLeft()
  column()
end

local function replant()
  turtle.select(15)
  turtle.suck()
  turtle.place()
  turtle.turnLeft()
  turtle.suck()
  turtle.forward()
  turtle.suck()
  turtle.turnRight()
  turtle.suck()
  turtle.place()
  turtle.turnRight()
  turtle.suck()
  turtle.place()
  turtle.turnRight()
  turtle.suck()
  turtle.forward()
  turtle.suck()
  for slot=3,7 do
    turtle.select(slot)
    turtle.drop()
  end
  turtle.turnLeft()
  turtle.turnLeft()
  turtle.select(15)
  turtle.place()
  turtle.select(2)
  while not turtle.compare() do
    turtle.select(16)
    turtle.place()
    turtle.select(2)
  end
end

while true do
  fell()
  replant()
end