There's lots of benefits and threats to forest, and given our current, pervasive, and severe ecological challenges, forests are more important than ever. However, it's not obvious what the best strategies are for mass reforestation, either for people vaguely interested in it or for the people who want to be passionately dedicated to it.
For example, if today I want to contribute to mass reforestation, what actions can I take? What about on the scale of a year, or a lifetime? This may make the question somewhat broad, but I envision an answer (maybe best as a community wiki) that lists specific things at different scales, overall answering the question: What are the most effective ways one can support mass reforestation?