Planting trees is clearly a 'good thing'. But you then need to protect, feed and water that tree as needed. The actual goal is to increase the number of living trees, not just to plant lots of trees. This may seem obvious, but planting trees is a common example of a gamed metric.
In my part of London, the local government plants lots of trees. But the trees are maybe too cheap, or not suitable for the location or not maintained. Most die. The next year they remove the dead tree and plant a new one - which quickly dies. They are doing great on the planting trees metric. But there is no increase in actual tree cover.