Seedlings of cirios are extremely rare

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During my 2008 trip, and again in the spring of 2010, I looked for seedlings.  Below are speculations from a search in December, 2008, along the highway about 50 miles north of Catavina.

On my evening walk, I tried to figure out the boojums.  The biggest question is—where are the seedlings?  I haven’t seen any small ones that didn’t already have a fat conical trunk forming.  But there must be a stage when there is just a little sprout, or cluster of little branches, before the fat trunk forms.  But I haven’t seen that stage, despite looking for hours.

The smallest cirio I found

Here are some possible explanations:

1. The sapling grows very rapidly, so they don’t remain in that stage for long.  I doubt this—since I suspect that many of these cactus, including the boojum, and quite long-lived.
2. They only reproduce in years when the conditions are just right, and such conditions haven’t occurred in recent years.  This is a likely explanation.  If so, what are those conditions?
3. They are not reproducing any more, due to grazing (which definitely occurs here), or climate change.  I doubt this, since all the other boojums, big and small alike, seem healthy.
4. I haven’t managed to spot any saplings.  Well, I’ve been looking for a long time.  I don’t think they are hiding under bushes, though some cacti do.  And, I’ve got a pretty good idea what they would look like.  However, it is possible that the very young tree looks quite different.  For a while, I was fooled by a bush that has rather similar thorny branches.
5. The boojum may have a population structure rather like mammals—namely, relatively few young, but the young survive very well.  Consequently, there aren’t as many young as in the case of organisms that produce thousands of young—most of which die.  The numbers game.  All the young ones I have seen look extremely healthy, except for one.  The trees less than two feet high are extremely well protected.  The growing tip has prodigious spines, and thorny branches arch out to protect the entire plant with an outer umbrella of defense.
6. I think 2 and 5 are the most likely explanations.
7. Next is the question of why they grow so tall.  The organ pipe cactus are probably more massive, on average.  They must have an extensive root system to pull water into the plant, where it is stored in the multiple fat arms.  But they are no where near as tall as the boojums.
8. I noticed that a number of boojums leaned away from the wind, the same wind as today.  But just as I thought I had spotted a trend, I saw some that leaned the other way.  Their leanings seem, at least to me, to be random.  Certainly not governed by light, of which there is plenty.  No competition for light here.  But if they are not competing for light, why grow so tall?  Why waste the resources?
9. If they are not reaching to the sky for light, then for what?  Suddenly it hit me—water!  That’s where the water comes from.  And here, there is often fog, and humidity is higher.  This morning, I saw that the little branches and leaves of the boojums had caught a lot of droplets.  Probably they have some way to absorb these droplets.  If there is a lot of fog here, then by reaching higher, they may make it into wetter air, or air that is moving faster, and hence bringing more water to condense.
10. The ocotillo (a relative) grows where there isn’t any fog.  Their long branches seem to be a good adaptation to avoiding grazing.  Not only are the branches spiny, but they are mostly out of reach of non-insect herbivores.  That long, skinny form of the ocotillo seems to have pre-adapted the plant to the possibility of growing even longer, to catch the fog.
11. Well, why not just have a giant ocotillo in the Baja fog desert?  One with many branches?  Well, some of the boojums do have numerous trunks; but most don’t.  If reaching high into the fog is the strategy, then it’s better to have one long trunk, than many shorter ones.  And, the short side branches of the boojum could collect the fog moisture as well as larger, multiple trunks of the ocotillo.  In addition, the side branches (or certainly their leaves) can be shed, if conditions warrant for the boojum. 
12. If I am right about the boojum gaining an advantage for being tall, then what about the young ones?  They are at a disadvantage, compared to the adults.  This might explain why there are so few saplings.  Perhaps they need a few years that are more wet than average to get going—to establish the “net” of branches, plus the fat trunk to store the water.  And since there are relatively few saplings, this puts a premium on protecting the ones that have made a start—hence the prodigious umbrella of defense.