Tenants may have different ideas about landscaping than you do. To prevent a chainsaw massacre, put a clause in your tenancy agreement that tenants are NOT to trim or remove trees or shrubs. Establishing value of plants is very difficult, prevention is better than cure.
If tenants request permission to trim trees (some will), ask they use Dazzle to mark what and where they want to cut, and email you photos for your consent and to keep a record of what was agreed. If they are serious about doing it, they will comply. If you never hear again, make sure you check on your next inspection that they didn't go ahead anyway. We know a landlord who had the unfortunate experience of a tenant 'trimming' a lovely garden full of established 5-7m high trees with a chainsaw. To waist high. Every single one. Surprisingly, the tenant asked permission and received it first , there was mis-communication about what a 'trim' involved. The garden lost a decade of growth. So use the Dazzle trick to prevent this sort of problem on your property.