Answer: Why are palm trees so tall?

Palm trees are wonderful, but very strange... 

As you might suspect, they're not ordinary trees, but something very, very different.  

They're generally super-tall, able to remain standing in hurricane force winds.  If you cut one down, you'll see a very strange and wonderful composite structure that looks nothing like an ordinary tree.  There are no tree rings, but a bundle of fibers that are key to its extraordinary resilience. 

P/C Wikimedia / Kadeve.

  
Our Challenge was:   

1.  Why are palm trees SO tall? 

As you know, asking Why Questions can be really difficult and tricky.  What's a good answer to a why question?  

To get a bit of background, I looked at the Wikipedia entry about palm trees, and quickly ended up on the entry for Arecacae, the latin family name.  There I learned that: 

The Arecaceae .. can be climbers, shrubs, tree-like or stemless plants.. There are 181 genera with around 2600 species are known, most of them restricted to tropical and subtropical climates. Palms are distinguished by their large, compound, evergreen leaves, known as fronds, arranged at the top of an unbranched stem. However, palms exhibit an enormous diversity in physical characteristics and inhabit nearly every type of habitat within their range, from rainforests to deserts...

I started this Challenge by doing an obvious search in the form of a question.  Note that asking questions like this triggers a special kind of Google search processing--it's not just searching for those terms, but the query is handled much more as a knowledge-based request... 

     [ why are palm trees so tall ] 

The search results are pretty good.  

(Click to see at full size.) 

The first 4 results are right on topic and give us a diversity of content.  Here's what I see and think when I look at these hits.  

#1 is a link to a Quora (a well-known question-answering site) discussion with a question about the evolutionary benefit for palms to grow so tall.  That's a great approach to answering the why question--understanding the costs and benefits from an evolutionary perspective would be good. 

#2 (skipping over the "People also ask" section) links to a reddit "Explain like I'm five" question/answer about "why are palm trees so tall?"  The explanation might be simple, but there's almost certainly an interesting discussion there. 

#3 is from Mother Nature News, a kind of gee-whiz site with breathless articles like "4 ways tardigrades are nearly indestructible," but might give us some interesting tidbits about tall palms.  

#4 links to a StackExchange forum, pointing to the more generic question "Why is it beneficial for trees to grow that tall?"  I expect this to be a more general discussion of tree height--perhaps we'll learn something about why trees grow so tall in the first place.  

I read the targets of these links and found out that: 

* Not all palm trees are tall!  (In retrospect, this is obvious--different species of palms have different heights. For instance, the Allagoptera arenaria  (Beach palm) is less than 2 meters high.  But clearly, we're curious about tall palm in this Challenge.)  

* Palm trees in their wild and natural setting often compete for resources.  In the wild, palm forests are often densely packed, requiring the palm trees to do something to grab their own light, water, and nutrients.  Growing extremely tall is one solution.  

Here are a few images of wild palm tree forests. You can see there's a lot of competition for sun and water.  

Eastern San Diego county, packed into the bottom of a dry ravine. 

A palm forest in Indonesia.

Even beach locations can be competitive! (Image by Pexels from Pixabay.) 

(I note that it's a little tricky to find images of palm trees in their wild and unstructured settings.  Many palm trees, even dense forests, are often former coconut plantains, which isn't the same.)  

Result #2 tells us that palms are often the fastest growing trees (although as with palm tree height, growth rates vary from species to species).  So they compete in height, and rate of growth in order to get the resources they need.  

Meanwhile, #3 tells us that the tallest palms are the Quindio wax palm (Ceroxylon quindiuense), growing up to 60 meters (180 feet), which Wikipedia tells us grows in dense forests in the wild--so height is important there as well.  

And #4 asks the more general question, "Why is it beneficial for trees to grow that tall?" Keep in mind that this is a discussion on a StackExchange site that encourages experts to answer and discuss questions.  It's heavily moderated, and the quality of the discussions you find there is pretty high.  

This particular thread discusses why palms in forests grow so tall, and work through various alternative explanations... but it all comes back a fitness advantage for taller trees to have more sunlight.  

An interesting twist...  Just for grins (and because I know that shifting media types sometimes gives an insight), I did a search for: 

     [ palm tree height ] 

and looked at Images.  It was pretty much what you'd expect.  Looked like this in the center of the SERP: 

That scatter plot chart in the middle made me think--perhaps there's something interesting here! 

Turns out that this chart comes from a scientific paper about the age and height of oil palm trees, Tree height and crown shape as results of competitive games (J. of Theoretical Biology, January 1985) and that made me think about doing a search in Google Scholar.  

In Google Scholar: 

     [ palm tree height ] 

led to a bunch of fascinating papers (which time and space prevent me from summarizing, but there's a fun intellectual rathole to explore one day).  

But the paper Competition from below for light and nutrients shifts productivity among tropical species
seemed to potentially hold the answer to our question.  Turns out that it didn't... exactly... but it DOES make the fascinating observation that 

"...In 2 cases the novel competitive mechanism responsible for the shift was reduction in crown volume, and therefore light-capturing capability, of overtopping deciduous trees by intrusive growth from below a palm." 

Which kind of captures what we found elsewhere.  

Why are palm trees so tall?  Answer: Palms compete for light by growing tall and fast.  In this case, they overreach the (ordinary) deciduous trees by growing up and through the canopy to reach the pure sunlight above the shade cover of the deciduous trees.  But in palm forests they're competing with their peers...  where they compete just as hard.  

Remarkable. 

Search Lessons 

This Challenge points out a couple of lessons to learn and take to heart. 

1. Looking across a number of different sources is valuable.  I know I keep saying this, but as a skilled SRS-er, do NOT lock in on any single result, especially if it confirms your beliefs.  A better strategy is to look broadly across a number of results and look for insights that are reported consistently across a number of different authors, different sources, and different perspectives.  That's one way to find your way to truth.  

2. Try different sources to get a different perspective.  Here I did another (but related) search on Google Scholar (after having been prompted by seeing a scientific chart in an image), and found lots of high-quality (but sometimes dense) articles on palm trees and their growth behaviors.  

Hope you enjoyed this romp through palm tree botany.  As always, there's a LOT more to say about this topic.  (If you're interested, a great query is [ varieties of palm trees ] -- they're an amazing group of plants with wildly varying shapes, sizes, and niches.  As they say, worth a trip...)  


Search on!