What is the underlying cause of the cleanup costs incurred by neighbors due to homeowners planting trees?

When homeowners plant trees, it can create a situation called a negative externality, which means that their actions affect others in ways that are not reflected in the cost of planting those trees. For example, if a homeowner plants a large tree that eventually grows over into a neighbor's yard, it can block sunlight or even drop leaves and branches, creating extra cleanup work for the neighbor. This means the neighbor has to spend time and possibly money to deal with the mess caused by someone else's decision to plant the tree. The underlying cause of the cleanup costs is that the homeowner does not consider how their trees might negatively impact their neighbors, leading to an unfair burden on those neighbors. Therefore, it's important for homeowners to think about the effects of their choices on others in their community.