Tunnel of plants

Hi everyone,  

I am  experimenting folding trees and connecting them. I'm planning to build a plant tunnel (like a greenhouse or growing tunnel) as part of a permaculture design. The idea is to grow Amazon cucurbits inside The tunnel ( too much sun destroy then), and outside the tunnel i'm gonna grow beans. I want to make sure the tunnel is oriented to maximize sunlight, maintain good ventilation, and work well with the local climate.  

My question is:  

What is the best orientation for a plant tunnel in permaculture, considering the sun’s direction, prevailing winds, and thermal efficiency?

For example, in terms of:  
- Long axis of the tunnel (east-west or north-south)  
- Roof inclination  
- Placement in relation to ventilation and natural shade  

Any practical experience or specific recommendations would be very helpful.  

Thanks in advance!  
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Just to be clear, are you in the southern hemisphere?

also in terms of wind, knowing where you are in general terms would potentially be helpful if you're near mountains, lowlands, etc.

Interesting project....So you are planning to create a living tunnel of trees for curcubits and beans to climb in and up. We've had a bit of discussion about simple living trellises, but making a tunnel to have an inside, as well as a outside structure gives the idea more functionality and complexity.
As Tereza points out you may have a conflict or compromise depending on the prevailing winds and terrain inclination.
Orienting the tunnel with the main axis North-South will mean that both sides get equal amount of sunlight (morning on one side evening on the other). If your afternoon sun is more intense, you may wish to reduce that exposure slightly by tilting the axis a bit.
Whether you get much of a draft through for ventilation inside the tunnel will depend on your local winds as much as anything. If you are lucky then the winds also go North-South. If not you will have to guess how much to compromise on solar aspect to gain ventilation. Making the trees wider spaced might help ventilate along the length through the sides rather than just through the ends.

If you use the right kind of trees, they can actually fuse to each other and create a strong living structure.
This thread about living bridges might give you information and ideas: https://permies.com/t/2112/woodland/Living-root-wood-bridges

That sounds like a great project. I don't have any advice or personal experience on the matter, but I was recently watching a video of a guy who has made a living tunnel using a polytunnel frame and covered it with espaliered trees as well as flowers and annuals. Maybe you can glean some useful ideas from it.