I am going to have to side with those who disagree with the Malikim desertification of the map. Firstly, desert is not capable of sustaining large populations by itself. There simply isn't enough water to support local wildlife for a population to live off of. Desert is thus considered a bad terrain to be in, much less live in. Historically, any settlement in desert was either due to there being some local source of water to drink which could also support large amounts of plants or animals to eat (a river or oasis), because all the good land had already been claimed (these people would remain more or less tribal unless some form of irrigation could be developed), or because there was something valuable there to trade in exchange for water, food, and hopefully some form of wealth. While of course this game is a fantasy mod, it seems to me that the tribals Varn found in the desert did not magically create that desert beforehand as part of some kind of a "lifestyle choice," rather they were already in the desert for one of the above reasons. Whilst life in the desert can make a people adept at getting the very most utility from such a terrain (well molded by the movement bonuses and such they have for deserts), such adaptations will never make desert preferable to more temperate climates in terms of supporting populations larger than a few hundred. Thus, the idea that after settling in some grassy landscape they would work to desertify it is illogical.
Secondly, lorewise the Malakim are supposed to be goodly followers of Lugus, lead by Varn, who are generally supposed to be forgiving, tolerant, honest people. I find it hard to believe that after taking a city, they would desertify the lands around the city, since in addition to the above that would also destroy the inhabitants way of life, and would only be done as part of some meglamaniacle scheme to "Malakanize" the population. Maybe the Order would attempt this sort of thing, but followers of Lugus I just don't see as the totalitarian type.
Finally, there are already at least two other civs that terraform their terrain, as well as a religion that terraforms the terrain of its followers. This feature I think has been used enough as is. Generally speaking, civs should reflect the terrain they are in, not the other way around. I personally would find it boring if maps regularly get divided into the ancient forest zone, the desert zone, the jungle zone, and the Ice/tundra zone(s), as determined solely by political boundaries. Give the Malakim something else if they need more "pazzaz" but not this oft-repeated mechanic. The Malakim having this sort of terraforming both cheapens the uniqueness of those civs which already do so, nor really adds anything to the game but more data for the game to crunch, slowing performance.
Generally speaking, the terraforming/tree planting spells are tedious micromanagement anyway, which if axed I would not miss too much.
.
