Individual committee members can’t make unilateral decisions. In practice, there might be some minor things for which it is reasonable to ignore formalities. Eg. one committee member, who knows about the common property lighting, might just go ahead and replace a bulb whenever a light is out and might just go ahead and call the OC’s usual electrician if replacing the bulb didn’t fix it.
Also, our ground contractor does routine pruning as they see fit to keep paths clear and for the general health and appearance of our plants. In addition, various unit owners and committee members might occasionally just snip off a bit that obviously needs doing without asking anyone. We might even remove a certain type of small tree that is not intentional and comes up as a weed around here.
If there was someone complaining that things were going beyond reasonable, trivial and flexible into unreasonable, substantial and unjustifiably unilateral, and that is what you are saying, then, as an EC member, I would want to cover our arses by being extra diligent about recording a resolution to do each thing or to formalise delegations to do things (eg. ‘Member X is delegated to fixing lights’). I would also say that we should be extra careful to make sure reasons for decisions were recorded. That way we could demonstrate our reasonable efforts to make the right decisions, openly, with transparency etc. Self-defence, even if we thought we were being entirely reasonable.
In practice members of committees I have been on would spend money on some routine stuff without asking each time and get reimbursed, but this was for things that were obvious and minor and the relevant people had done it before and always kept receipts and so on. Eg. buying some replacement light bulbs. We were always able to rely on committee members’ good sense to know when something was no longer minor and needed a committee decision. Eg. We have a budget for tree surgery and one person tends to handle tree matters (Handily, she has a forestry degree so knows about trees). She would get quotes for what she thought needed doing, but she would not go ahead until her recommendation had been approved by the committee. Also, we would not go ahead with any substantial work on a tree until she had talked to the unit owners that might be effected by it.
So, no, your chair should not unilaterally approve pruning of common property trees, at least not if it was obvious that it would have an effect on your unit.
As it happens, I was subject to just this sort of complaint not long ago. I helped a neighbour remove several leggy and overgrown large bushes/small trees from her unit boundary. One of her neighbours complained that we had also removed stuff from her garden (We didn’t.) and that we had effected the privacy and outlook from her unit (It could not have.). The accusation was quite bizarre because she would have to be able to see through a brick wall for the plants we removed to have had such an effect. We had talked to the people who could plausibly have been effected and they were all happy with the gardening we were doing.