I need to put a post down to support a carport. The post would be embedded in a concrete block approx. 60cm x 60cm. This is 3 metres from the trunk of a Japanese Maple about 5 metres tall.
Is there a likelihood of damage to the tree if we are careful in digging the hole, and how can I help it?
It's anybody's best guess really - where the roots of a tree spread to is very much down to local conditions, and the only way you're going to find out is to start digging the hole. At a distance of three metres from the trunk, it's likely you will come across some root material, and losing a little of it shouldn't cause too much damage, particularly at this time of year (assuming you're in the northern hemisphere), but if the whole area is a solid mass of roots, both large, woody ones and fibrous ones, then yes, your tree will suffer and may even die.
Ultimately, if you need to put in a post, then you need to do it, and you may have to replace your tree if putting up a carport is a priority, but you might find it's not an issue when you start to dig out.
It partly depends on the size of the tree (some Japanese maples mature far larger than others, and at 5m tall, there are a lot of possibilities.), but at 3 meters from the trunk, you are more likely to damage a larger tree than a smaller one. In any case, you are unlikely to kill the tree, even if you do cut some roots. That will be such a small percentage of the root system. Sometimes if I feel I've cut back more root than normal I'll prune the top-growth a little, to balance the systems. If you do this, wait until spring, so you don't get winter burn from it.
