Analyzing the impact of tree planting is good to mitigate side effects... but it is interesting that western industrialized society at the same time creates incentives for bio-mass energy plants which have to mow down great swaths of standing forests in order to have enough fuel to operate.

With such rampant deforestation of important global carbon sinks, caused by agriculture and industry, reforesting programs are an important component to counterbalance the impact of western agriculteral and industrial impacts.

See Michael Moore documentary: Questions the true cost/benefit of different green energy technologies and programs.