I commend you for asking the right questions about permission to climb because a lot of people including me have been asked to come down out of a tree. We have nice phrases like “Ninja Climbing†that help soften the impact that you are trespassing no matter what you call it. Then there is the stealth techniques like wearing forest hues and haul all your rope and gear up with you when you trespass certainly off the beaten path. Large trees attract all kinds of people so select your target well. I would first talk to the local arborists that climb without pole spikes and see what their opinion is of the city forester. Most never climb for fun but some train for annual contests. They most likely know each other and you will learn who the person to pay a personal visit to is. I find there are many layers to peel and may suits that have to be asked that consider your request another task to get in their way. Usually the first response is negative because no one has ever asked and to grant permission involves them with all kinds of legal tangles. Everyone is concerned about getting sued and without insurance coverage they can deny with just cause. Then how can you prove you know how to climb safely? I would encourage you to seek instruction that results in some kind of skills review and written test. Proof of knowing safe skills has to help. Having a reason to climb other than it is so fun to do so is also helpful. Wildlife study, photography, bat boxes, kite retrieval, nut collection, swing installation, you get the idea. It is not easy most of the time and then there are those who will say go climb where no one can see you and if anyone asks you never asked for permission. Isn’t that just peachy; Plausible deniability. Here in Kansas City three of us are practitioners for hire to conduct climbing events for many parks and recreation departments. They list us in their catalogues, collect fees and we invoice them per climber. They let us climb anytime we want since we have completed all the red tape, filled out the forms, conducted background checks, certified in first aid and CPR, named them as additional insured, ad nauseaum.
Visit the TCI “Climber Finder†and always use protection.