Yeah, it's a thorny problem strud, I'm facing a similar design challenge at our new place...the eastern side closest to the house which would be perfect for a good sized Zone 1 area, is dominated by a couple of mature eucalypts - which even if left there (our sun up here is strong and consistent enough all year to mean vegies only need 3-4 hours max a day) would cause significant litter and extended allelopathic root problems.
My solution is going to be full removal of the eucalypts, with a combination of establishment of more suitable long term high canopy species (outside the proposed bed area), plus intercropping (in the actual proposed bed area) of fast growing, short lived leguminous species which grow to 2-4 metres, for more immediate shade.
I'll be predominately using Cajanus cajan (Pigeon Pea) and Sesbania Grandiflora (Agati), but both those species might well struggle to reach their potential in your climate...perhaps vigorous annual pole bean varieties densely planted at the northern (and perhaps even western) edges of your beds (or even outside if they're small beds) and trained over mesh (sloping in to the center of the bed to maximise their shading capacity) to shade at appropriate times of day might be the way to go. You can adjust a mesh frame for pole beans pretty easily to get the right sun when you need it as the season and sun height alters. Other annual climbers and vines may also be suitable options.
That way, if you remove the euc's, you'll be able to shade in summer but have full sun in winter. All the appropriate temperate species I can think of offhand would be too rampant to intercrop with annuals in relatively small raised beds - but that's not to say there isn't a viable option.
The other alternative so you can keep the euc's, might be to leave the summer beds fallow, or planted out with a low sunlight requirement green manure, or run your chooks over them, then build winter beds elsewhere - but if the spot you have is perfect for both seasons bar the euc's, I'd be inclined to remove them. But as Bill very rightly said, do consider the full range of benefits they bring first.
We're in a location where area for beneficial wildlife habitat outnumbers land area people take up many thousands to one, so removal of a couple of euc's is a very simple choice - your situation is perhaps very different.
The real path to natural farming requires that a person know what unaltered nature is, so that he or she can instinctively understand what needs to be done—and what must not be done—to work in harmony with its processes. - Masanobu Fukuoka
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