Walking Palms

I don't know about you but Socratea exorrhiza has to be the strangest species of palm that I have ever laid eyes on. Native to Central and South America, its peculiarly stilted appearance has earned it the common name of "the walking palm." Whereas most palms invest in heavy trunks, the walking palm sends out a lanky set of stilt-roots upon which the palm grows like some otherworldly tripod.

There has been a lot of debate over the last few decades as to the purpose of these stilt-roots. In 1961 it was suggested that they were an adaptation for living in swampy areas. To date, no evidence of this has been found. Others have suggested that these roots are relatively cheap to produce compared to a solid trunk, thus allowing more investment in growing taller in a shorter amount of time while still maintaining structural integrity. This sounds attractive and is probably part of the puzzle. However, I feel that a particular study published in 1980 offers the best explanation.

Tropical forests are full of decomposition. The omnipresent threat of rot means there is a constant rain of limbs and snags from the canopy above. Trees regularly topple as well. For most plants, getting flattened by such debris is usually fatal. This is not necessarily so for the walking palm.

It has been observed that walking palms flattened by a fallen limb or tree can actually "walk" themselves out from underneath. Since most of the trunk is capable of producing stilt-roots, it doesn't take long for a new anchor to become established. Once this occurs, the palm is free to continue its journey into the canopy.

Getting squashed isn't the only worry either. Light is a premium in the deep shade of a rainforest understory. It is also short lived. A hole in the canopy that provided ample light one week may quickly close in the next, removing the life-giving rays of the sun. If a plant were able to "move around" it could potentially relocate to a sunnier spot. In a sense, this is what the walking palm does.

Walking palms are positively phototropic, meaning they lean towards a light source. Leaning can put stress on a trunk to the point that the tree topples over. The walking palm gets around this by sending down those stilt-roots, which provide support as it chases light through the canopy. In a sense, this palm "walks" itself around the forest in search of the best light. Whereas most trees are stuck where they germinate, the walking palm has, in a sense, freed itself from such restrictions. As such, older trees are often found far from their original germination point.

Once in a favorable location, the walking palm will right itself and continue upwards. At this point, the old trunk and roots are superfluous and will often rot away. For a young tree, this process can happen in as fast as two or three years. This is an incredible feat considering the time scale most trees operate on. Personally I would love to be able to observe a forest with walking palms over a few decades. Seeing how their positions change with time would be fascinating. At the very least, their bark is often covered in epiphytes, which offers a lot to comb over on our timescale.

Photo Credits: Hans Hillewaert (Wikimedia Commons) and John H. Bodley and Foley C. Benson (infographic)

Further Reading:

http://www.revistas.ucr.ac.cr/index.php/rbt/article/view/5955

http://www.jstor.org/stable/2387775?seq=1#page_scan_tab_contents

Insect Eating Bats Eat More Insects Than Birds in Tropical Forests

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If the early bird gets the worm, it is only because we haven't been observing bats the right way, at least not in the rainforests of Central America. It has long been thought that insects such as katydids and caterpillars exhibit night feeding in order to escape day-active birds. This theory has influenced the way in which researchers investigate insect herbivory in tropical forests. However, recent studies have shown that bats, not birds, are doing the bulk of the insect eating in both natural and man-made habitats. 

In order to accurately investigate the role of insectivorous bats play in limiting herbivory in tropical forests, researchers decided to look at the common big-eared bat (Micronycteris microtis). They wanted to find out exactly how much insect predation could be attributed to these nocturnal hunters. As it turns out, 70% of the bats diet consists of plant eating insects, which is quite significant. Extrapolating upwards, it was apparent that we have been overlooking quite a bit.

Using special exclosures, researchers set out to try to quantify herbivory rates when bats and birds were excluded. What they found was staggering. When birds were excluded from hunting on trees, insect presence went up 65%. When bats were excluded, insect presence skyrocketed by 153%! What this amounts to is roughly three times as much damage to trees when bats are removed - a significant cost to forests. 

To prove that it wasn't only natural forests that were benefitting from the presence of bats, the researchers then replicated their experiments in an organic cacao farm. Again, bats proved to be the top insect predators, eating three times as many insects than birds. This amounts to massive economic benefits to farmers. Bats have long been viewed as the enemies of both the farm as well as the farmers. Research like this is starting to change such perspectives. 

This certainly doesn't diminish the role of birds in such systems. Instead, it serves to elevate bats to a more prominent stature in the healthy functioning of forest ecosystems. Findings such as these are changing the way we look at these furry fliers and hopefully improving our relationship as well. 

Photo Credit: Christian Ziegler - Wikimedia Commons

Further Reading: [1] [2]
 

Is it a Fungus? Is it a Forb? No, it's a Tree!

Botanical gardens are winter sanctuaries for a northerner like myself. Winter tree ID can only do so much for me during these times. As such, I try my best to make regular trips to tropical houses wherever and whenever I can. On a recent excursion to the Missouri Botanical Garden, I came across something completely unexpected.

I was perusing their tropical house aptly named "The Climatron." As I rounded a corner I happened to look down and saw what looked like something only a member of the birthwort family (Aristolochiaceae) could produce. There, lying near the ground were a cluster of some of the coolest flowers I have personally laid eyes on.

I began searching for the plant that produced them. Up until this point, I have only encountered members of this family in the form of low-lying understory herbs and scrambling vines dangling from the canopy. There were no apparent leaves associated with these flowers and the part of my brain responsible for search images became confused. I traced the flower stems to their place of origin and realized they were attached to the nearest trunk. I followed the trunk upwards and realized that what I had found was in fact a small tree!

The species I was looking at was none other than Aristolochia arborea, a small tree native to the tropical forests of Central America. Needless to say I was floored. There is something to be said about any plant family than can vary this much in size and habit. The coolest aspect about this tree is that, similar to the more herbaceous members of this family, the flowers are produced close to or directly on the forest floor.

A closer inspection of these strange blooms reveals an interesting morphology. It would appear that they are mimicking fungi in the genus Marasimus. Now this could simply be a manifestation of apophenia. Was I seeing patterns where there are none? Of course, this was a job for scientific literature.

It seems I may have been on to something. Botanists agree that in the wild this plant is pollinated by fungus gnats and flies. However, no direct observations of this have ever been made. That being said, the flowers do emit a rather musty smell that could very well be described as "fungal." Regardless, this is an excellent choice of tree to showcase in a botanical garden because stumbling into it like I did led me down an curious path of discovery.

Tree photo credit: Cymothoa exigua (Wikimedia Commons)

Further Reading: [1] [2]