[hnmullany]

Vegetation-type is determined by temperature and precipitation. You can't un-desertify a true desert unless you irrigate. Most of these projects that "succeed" - miraculously correlate with good rainfall experience.

Most of the Sahel revegetated all by itself, when the decadal drought ended in the 90's.

Re-vegetation projects can help put vegetation back when it's been removed by shitty management practises like severe over-grazing.

It can also help speed revegetation if there are no nearby seed sources and dispersion speeds for those species are low. But dry-adapted vegetation seeds can usually persist for very long periods of time waiting for water.

[mlinksva]

> unless you irrigate

One of the reasons for the interestingness of speculative proposals like Qattara, seawater-for-Salton, and it turns out an even more ambitious project to pump seawater from the Bohai Sea to Xinjiang.