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Are there any narrow columnar/fastigiate tropical trees?  RSS feed

 
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When growing trees native to temperate zones, practically every angiosperm or gymnosperm species that has multiple cultivars has at least one columnar cultivar.  But columnar cultivars of trees native to tropical zones seem to be practically nonexistent, at least I can't find any.  Even among popularly grown species with multiple cultivars such as avocado, cultivars described as "columnar" are still fairly broad, just not as broad as the non-"columnar" cultivars.  There are none as narrow as a lombardy poplar or columnar apple or plum tree.  Why is this?
 
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Palm? Papaya? Chaya?
 
Mike Turner
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Should have been more specific.   I'm asking about dicot trees, not monocots or plant growth types that have no temperate zone equivalent (palms, papayas, etc.).
 
Mike Turner
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So why is it that columnar cultivars are "dime a dozen" among temperate zone dicot trees and conifers, while being practically nonexistent among trees from the tropics?  Among the tropicals, I could only find a single cultivar of Erythrina (Erythrina variegata 'Tropic Coral') that was columnar.  In hibiscus, the temperate Hibiscus syriacus (rose of Sharon) has several columnar cultivars, whereas the tropical Hibiscus rosa-sinensis, the common tropical hibiscus, which has 100's of cultivars, has none.  Anyone care to speculate?
 
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Mike Turner wrote:Anyone care to speculate?

Maybe there's more of a demand for columnar temperate trees?  Maybe the biology makes it harder to create a columnar tropical tree?
 
Mike Turner
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Mike Jay wrote:

Mike Turner wrote:Anyone care to speculate?

Maybe there's more of a demand for columnar temperate trees?  Maybe the biology makes it harder to create a columnar tropical troee?



I can't see why there wouldn't be a demand for columnars in tropical landscaping and orchards.  Columnar fruit trees makes it possible to shoehorn a bunch of different fruit trees into a small garden.  Columnar trees are very useful in formal garden design.

What aspects of tropical tree biology would make the columnar shape difficult to select for when compared to temperate tree biology?  I'm just trying to figure out why there is this disparity.  There are literally 100's of columnar cultivars of temperate tree, but almost none for tropical trees.
 
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Beats me, I was just speculating...
 
Mike Turner
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Since few seem to want to speculate on this, here are my thoughts on the matter.  In the the lower latitudes during the day, the sun spends most of its time high in the sky so the light is coming from above most of the time.  The best tree shape under these conditions is broad and relatively flat topped (think mimosa tree shape) with only enough height to keep above the tree competition.  Conversely at the high latitudes where the sun spends most of its time near the horizon so the light is coming from the side all of the time, the best tree shape is tall and narrow (columnar), which is the shape seen in trees of the taiga forests.   In the mid-latitudes the optimum tree shape is intermediate between these two.

Our temperate trees weren't always growing where we find them growing today.  From the time that angiosperms first evolved over 100 million years ago during the Cretacious until about 8 million years ago, temperate trees were growing up near the arctic circle as part of the polar deciduous forest (the conifer and ginkgo lineage in that location goes back even further).  Then, starting 8 million years ago, as the climate cooled down into the Ice Ages, these trees were pushed south into the mid-latitudes. As they moved south, their shape evolved away from the columnar shape most efficient at the high latitudes into the broader shape that works best at their new home in the mid-latitudes.  But those ancient genes for a columnar shape are still there and it is relatively easy to pick them out of the mix when selecting for new cultivars.  

There are also narrower cultivars of tropical and subtropical trees such as avocado and Virgnia live oak.  These aren't columnar, but are narrower than their typically broad wild type shapes and are are typical for the shape of mid-latitude trees, ancient genes going back to when these trees were growing in the mid-latitudes over 8 million years ago.  But tropical trees have never grown in a high latitude location where a columnar shape would be optimum and so have never evolved the genetics for it, hence the dearth of columnar tropical trees.

Interesting, while researching this, I came across papers about fossil dendrochronology showing that the trees  growing in the polar forests during the Cretacious were about twice as productive as their modern taiga equivalents, no doubt due to a combination of warmer temperatures, longer growing season, and higher co2 levels at that time.
 
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For any tree that's a single specimen, I think it's important in the tropics for it to provide adequate shade for its own root zone. And this is readily achieved since the sun is fairly high in the sky by 9 a.m. . Sun on the root zone is not necessarily A Bad Thing in the Boreal forest. It can be very harmful in the tropics. I was at a couple different tree nurseries in the Philippines, and they always provide partial shade for young specimens.
 
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