This problem can be solved with a new property tax and environmental regulations on where and how buildings can be built.  Property taxes, especially if the property is not a permanent residence and if the property is located in a sensitive area, should be correspondingly higher. Adjust legislation to allow for this. And this applies not only to Italians in the Karst, but also to Slovenian weekenders in Pokljuka, the English in Goričko, etc. Even if an Italian buys a property in the Karst, acquires a permanent residence, cultivates a plot of land..., or renovates a dilapidated house - there is nothing wrong with that. But if he is only there for a weekend, he will contribute more to our budget.
The problem is also the responsibility of the local authorities who / if allow construction and certain activities in sensitive areas. This is not the fault of the Italians.