NZ is on the Pacific ring of fire, so if it ain’t volcanos it’s earthquakes. I can see 5 extinct cones and one live volcano from the hills above my land. Several NZ cities are build right on volcanos (Auckland being one) and some of our ports are flooded volcanic craters (Wellington). So it’s just life. Volcanic soil is great…
I have had no luck with plums. Beautiful fruit ..but lots of rot, or pollination problems. I think Tweva mentioned how pests and diseases make fruit growing such a problem these days. You have to find types and varieties that will grow without sprays as these may not be available post SHTF. Tho it is reasonable to stock up on some sprays for vegetables, to ensure you get something, it is better to grow what grows easily. The only way to really find out is by trial and error. If something grows like a weed… then that is a good food source… even if it is not the most tasty.
We can grow chestnuts here… European chestnut , and hybrids with the oriental chestnut. Big nuts .. but no so sweet. But you get heavy crops of nuts from a big tree .. which is a lot of food. No work except picking them up. A good SHTF food source. Wallnuts are similar .. tho not so fast growing.