There is no standard answer that will fit every possible scenario, as every site and circumstance is unique. The best way forward is to always seek the help of a tree professional to help advocate and understand the situation and to suggest the best possible path forward – both from the tree’s health, sustainability and longevity perspective, but also from a neighbourhood relationship perspective.
Some trees in this scenario are protected by local councils, and some trees' form and structure grow in such a manner as to prohibit ‘pruning the tree back to the fence line’, as it may lead to a potential risk of over-pruning the tree and or detrimentally impacting the tree’s health.
Generally speaking, neighbouring tree branches can be pruned back to fence line, or just beyond, or as discussed and approved by the owner, to attempt to best meet Australian arboricultural pruning standards and practices. These branches can then be given back to your neighbour, as they belong to them.
However, the practice of pruning your neighbour’s tree branches and then throwing them back over their fence is not a practice that we recommend. We highly suggest calling us to come and help find a reasonable solution, mediating for the best scenario moving forward, which may include pruning and removing branches with both parties contributing to the cost.
If in doubt, we recommend seeking advice from a suitably qualified legal professional.