If CO2 was in very small amounts then it would be the limiting factor of photosynthesis, this means the process will take place at a much slower rate because it is lacking one of the raw materials it needs for the process to occur. To find the optimum light intensity you really need all other factors to be at optimum levels or in abundance.
I think this is a good plan. In this way, it would stop flooding in the future. Trees help absorb water with their roots. It can absorb at least 20% of the flood water.
However, there are also factors that would affect the trees from growing healthily. Some of the trees would not receive the right amount of energy and sediments can possibly be mix with the good soil.
It is best that we examine why the flooding occurred. There could be other possible reasons for flooding. It can be pollution caused by people throwing their garbages anywhere.
