The multifarms have an orchard setting. I haven't used them myself but from what I have seen you wait for the trees to mature and then the multifarm harvests them and they go straight into the multifarms inventory. If you have already messed around with multifarms you will know that you just need to put the right electron tube into the intricate circuit board. There is a good list of what the electron tubes do on the forestry wiki.
Alternatively, you can put a wooden golem beneath the tree and he will pick up all the nuts when they drop. The cheapest but clunkiest solution would be to have an array of either vanilla hoppers, obsidian pipes or transposers underneath the tree but I wouldn't recommend that if you have the resources or the research for the other two.
You have to setup the circuit for orchards under the manual farms tab of a soldering iron. All the info is on the Forestry pages. You have to set the dirt and plant the trees yourself, but it will auto harvest.
Anyone know if the multi-farm orchards and sweet chestnuts are bugged in Forestry 22.214.171.124? I've set it up in my 1.5.2 world EXACTLY the same way as I did in my FTB world (where it chucks out barrel-loads of chestnuts) and... nothing
It takes a while for the trees to mature before they start producing fruit. It is not instant. Just let it run a while. You will see the fruit on the leaves change color after a while. Once the whole tree is like that, it will continuously harvest fruit/nuts.
Interesting... these trees are massive, in fact 1 tree will practically cover an entire largest multifarm, you may (haven't tried) be able to position 3 strategically so the farm might harvest 3. Is it really worth doing using a multifarm?
I've now got 4 trees planted on the 3x3x4 multifarm so there's lots of leaves poking over the edge of the farm. I read on the internet (so it must be true) that multifarms will still harvest fruits from those overhanging boughs - we'll see...
Multi-farms weren't my first choice since I'd used them before. I did try using an MFR fruit picker but it just looked at me like I was a retard