I'm interested in doing silviculture in my pastures. The usual practice for that is N-S tree lines for reasons of the suns affect. But I've seen keyline systems that put them on contour (or rather w.r.t. controur as it may slope off of it as it falls towards the ridgelines).
its an interesting question as following the Keyline geometry as we prefer sometime is sub-optimal when it comes to climate factors such as wind protection and more often than not solar access. You can remedy the latter by species selection and management if you want stick to the Keyline pattern that is! Species selection by determining your equinox and solstice sun angles at different times of the day (use cross sections on graph paper) and choose species that max out at specific heights. Remember that a lot of livestock we are sheltering are no more than 2m high and so a 3-4m high shelterbelt is going to be ample protection and is often the managed heights of traditional hedgerows in higher latitude climates for that very reason (balancing solar access and shelter). You can also go deciduous as well. Management is also a factor where taller species are involved: you can clearwood prune timber species at wider spacings to allow lower angles of light to penetrate through as well. Its all where design comes in and why I am such a fan of cross sections, graph paper, online sun angle calculators and protractors!
Hope that this helps,
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