Very good points made throughout @mountainwashere. :c)
The truth is that the success or otherwise of a project tends to be measured through human-centric metrics. Would certain aforementioned forestation projects have been deemed a failure had there not been a drop-off in land productivity over a few years? The answer would likely have been in the negative.
A departure from such human-centricity permits a more holistic approach better-compatible with the ways of the Native Americans and others who remained spiritually close to the lands upon which they lived.
In the relative absence of such an affinity one would indeed need to engage the environment with caution and knowledge (the latter only coming about through drawing upon that which has been tried and through progressive experimentation).
And through beginning with a single project in, say, Algeria one would be indulging in that spirit of experimentation and learning that would constitute less of a shove and more of a nudge in the context of the entire Sahara (and there would be plenty of Sahara remaining for species encountering hardship from those nudges to retreat into).
You are very correct in noting that humans are better at thinking short term than long term. We want gratification. We want it now. It drives our decision making process - often enough to ruinous ends.
However one should also recognize that the story of humanity's journey toward achieving flight was strewn with failures and learning before the first rays of success led to a continuing era where commercial flight has grown to be the norm.