Carport with permanent founation was put up by tenant can they remove it

Any permanent structure they install becomes part of the property. They could remove it but they would have to restore the property to the condition they received it in. Otherwise the landlo9rd can sue for the costs to restore.

First they could ( or should not) have put any foundation in without getting permission from landlord, so what did their written permission say about it.

Ok, assuming not, they will have to remove any and all foundation and bring the rental back to the exact condition it was when they rented it. If they removed the carport and not the foundation, the landlord can require them to pay for the removal of the foundation and landscraping to return it back to "as was" condition.

In fact if they installed the carport without permission, the landlord could require that anyway, but could allow it to remain if it was an improvement and they agreed.

The real issue it could or should never have been built without prior permission and agreement to what would happen

Any permanent structure they install becomes part of the property. They could remove it but they would have to restore the property to the condition they received it in. Otherwise the landlo9rd can sue for the costs to restore.

If renter has put in fence and planted trees, do they belong to the property owner

Do plants and fencing put in by the renter belong to the property when they leave

do plants and fencing put in by the renter belong to the property when they leave

Yes.

do plants and fencing put in by the renter belong to the property when they leave

If the tenants install a nice fence on your property, it's yours. If they plant plants or trees, they're yours to keep. The tenant cannot remove anything that is permanently attached to the ground such as a fence or plants planted or trees planted. Sure, they can buy it and plant it, but they can't take it with them when they leave as it becomes a permanent fixture of the property.