cool climate forest garden and yield

I have an area of our garden which I think to convert in a cool climate forest garden. I watched some videos and I know how well stuff grows under trees in more subtropical or warm temperate gardens but in cool climate? All they say is that you need to open the canopy more - then you are basically back to the "normal" garden. How productive are these gardens? On top of it I don't want fruit there because the birds eat it all if I don't net. In subtropical climates there are so many species which I could plant like cooking bananas or sweet potatoes. Does anyone have a really productive cool climate food garden (I don't mean tons of mint or firewood - something to eat!).

Alan Carter's book "A Food Forest in your Garden" is focused around Scotland, so rather cool I think. Granted the species available will be difficult from Scotland to Australia, but the type of plants should be similar.

I really liked the book, I recommend it to you. Page 103-272 are devoted to edible plants and how they can fit into a Forest garden. Many were familiar to me, but many many more I had never even heard of.

I would suggest looking for native plants that grow well in shade.

Look for shade-loving perennials that the pioneer to your area planted and ate.

Also include shade-loving native wildflowers for the pollinators.

Cane berries, persimmon and pawpaw all come immediately to mind.
I'm in zone 6 and birds seem to leave enough of each of these to make foraging possible.
Nut or acorn trees mean fighting squirrels instead of birds, which may or may not be easier.
One traditional way of harvesting nuts/acorns is with pigs, but for some smaller nuts, turkeys or big chickens might do.
Hardy yam could yield yam berries, but digging out the actual yam  might be impractical.
Groundnuts also could thrive, but again digging the out from between tree roots seems daunting.
Hardy kiwi vine likes a certain amount shade, but , it's fruit that may tempt birds.
Siberian pea makes food that is fairly pest resistant.
I think ramps grow in forests.
Redbuds have their buds.
Grape, linden and mulberry all have edible foliage.
Maple can be tapped for syrup.

It took me a while to get back to the thread! With pesky birds I mean pesky. I have about 10 hazelnuts growing and don't get a single one. And I don't get a single apple if there is a net over the tree...
I am still designing the thing in my head... I think of chinese toona.

One thing that works for me bird-wise is providing another food source which they prefer.  I have a tall mulberry tree that fruits around the same time as my currants, cherries, and raspberries. The birds mostly gorge themselves up high in the mulberry and leave the high-value (to me) fruits in the lower level to us humans.
May or may not work out depending on your local conditions.

I don't find anything grows well under trees, things will grow around trees but not under them. Spring ephemerals are an exception and some things can survive but you don't get any yield from them. Forests here don't have an understory as such, only where paths have been cut or trees have fallen do you find any of the berry bushes or other interesting things.

BUT you are not as far South as I am North so your sun is probably stronger and it should be possible to grow things in deeper shade than I can.

Have you seen the video tours of Paradise Lot before?   They are/were located in Holyoke MA and the amount of things they grew in a tiny city lot in a cold climate is astounding.   I was lucky enough to visit and do a volunteer day,  super inspirational place.