birch

local function harvest()
    turtle.dig()
    turtle.forward()
    for i = 1, 6 do
        turtle.digUp()
        turtle.up()
    end
end

local function goDown()
    while turtle.detectDown() == false do
        turtle.down()
    end
end

local function plant()
    turtle.up()
    for i = 1, 6 do
        turtle.select(1)
        turtle.placeDown()
        turtle.back()
    end
end

local function checkFuel()
    if turtle.getFuelLevel() <= 200 then
        turtle.select(16)
        turtle.refuel(16)
        turtle.select(1)
    end
end

local function itemsOut()
    for i = 2, 15 do
        turtle.select(i)
        turtle.dropDown()
    end
    turtle.select(1)
end

while true do
    if turtle.detect() == true then
        checkFuel()
       for i = 1, 6 do
            harvest()
            goDown()
       end
       plant()
       turtle.down()
       itemsOut()
       sleep(1800)
    end
end