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There is no other way around it--Madagascar is an evolutionary uniquety. 80% of the island's species live nowhere else on Earth. Among this uniqueness is a habitat that seems to come out of science fiction: The Spiny Forests.

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These forests grow in the western half of Madagascar, where the mountains that split the island in half bar rain from passing through. These forests can survive months if not years without rain, and the plants have to come up with certain adaptations for such meteorological hostilities. Most are armed with thorns and needles, which help retain moisture loss, whereas others have given up on leaves and instead photosynthesize through their trunks.

The spiny forests of Madagascar are one-of-a-kind, separate from the other rainshadows of the world--the Mojave in California, the Atacama in Chile, the Judaean in Israel, even the deserts of mainland Africa's northern half. But does it have to be? Could spiny forests similar to those in western Madagascar grow in the other rainshadows around the world?

(Side note--don't bring up the saguaro forests of the Sonoran, because saguaros are cacti, not real trees.)

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    $\begingroup$ Why not bring the cactus up? Convergent evolution would make a case that the principle is not just a random fluke. $\endgroup$ – o.m. Oct 16 '18 at 4:34
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    $\begingroup$ The suitability of the area for plant growth dictated the evolutionary route of those plants for this reason not bringing up the Cacti would be like ignoring Diesel vehicles when talking about the modern use of cars $\endgroup$ – Blade Wraith Oct 16 '18 at 7:59
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Some could, others won't; the Spiny Forest receives an average of 500mm of rain annually. To be able to support a similar ecosystem, this is how much rain the rainshadows would need to receive.

Of those you listed, the Judaean Desert is the only one that receives enough rainfall to support a similar ecosystem. The Mojave's rainfall is only a tenth of what it needs to be, and in the Atacama there are places where it has not rained in all of human history, and the average across the entire desert is just 15mm annually.

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  • $\begingroup$ This was in the VLQ queue, so I took the liberty of editing it slightly to make it clearer how it answers the question. I hope you don't mind. I think it's a pretty sensible answer. $\endgroup$ – F1Krazy Oct 16 '18 at 11:34
  • $\begingroup$ @F1Krazy All good, it does read better; I did mean human history not recorded history when I said how little rain the Atacama gets though, there are fossil raindrops from the last time it rained a couple of places that are tens of millions of years old. $\endgroup$ – Ash Oct 16 '18 at 11:37
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Dailey questions are always a challenge for me, because - what is the question? Here I take the question to be: could a really weird forest of unique dry adapted plants occur elsewhere in the world?

Yes. Here is Socotra.

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https://www.nationalgeographic.com/photography/photo-of-the-day/2015/12/socotra-island-ngpc2015// Depicted - Dragons Blood tree towering over stunted forest of Bottle trees. Socotran vegetation is unique and weird (maybe weirder) for the same reasons Madagascar is - it is an isolated island and it is dry.

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  • $\begingroup$ What do you mean, "what is the question?" $\endgroup$ – JohnWDailey Oct 17 '18 at 0:52
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    $\begingroup$ You could also consider the Joshua Trees of the Mojave as "wierd" and spiky: en.wikipedia.org/wiki/Yucca_brevifolia $\endgroup$ – jamesqf Oct 17 '18 at 3:06
  • $\begingroup$ "What is the question?" is meant to convey my uncertainty, and explain why in my answer I then go on to state my (now qualified as uncertain) understanding of the question. Persons with a clearer understanding of the question such as yourself might then weigh in to either correct me or confirm my understanding. $\endgroup$ – Willk Oct 17 '18 at 15:10

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