Take it from this iguana, or from the red and ready labios de mujer: Phyte Club isn’t morphing into a blog about Costa Rica. Plant-wise, I’m not even that in to the tropics. However, I did just spend the first couple weeks of December tromping the country’s slippery trails, which necessitates at least a few posts. The nature there is effortlessly extravagant. And though the ecological interdependency isn’t greater, per se, than in the Cali desert or coastal foothills, there’s a lot of different stuff going on. Be prepared for mucho green. As the local “Ticos” say, “PURA VIDA”.
Available square footage is at a premium in tropical rainforests. No patch of soil goes unused, and beyond that, no surface goes unused: they’re the cities of the floral kingdom, with plants stacked on top of each other like urbanites in 20-story apartments, fighting and loving their way toward life and the cosmos in one seething system. It is interdependency in the extreme, and examples of cooperation, competition, and adaptations abound. Here are a few of the most notable.
Whenever a gap opens up in the forest, say, when a tree falls, it is quickly colonized and filled in by plants eager to access the rare streams of golden rays. Since the canopy is normally “closed”, sometimes several times over, by the multi-layered foliage of trees and tall herbaceous plants, rainforest species are constantly competing for available sunlight. It is one of the main limiting factors for growth in this system.
So, a lot of plants deal with this by having broad, bright green leaves, positioned perpendicularly to the sun’s rays in order to intercept as much solar radiation as possible.
Or how about this plant dubbed “elephant ear” (Xanthosoma sp.) due, obviously, to the leaves’ resemblance to a pachyderm’s big floppy ears. Unfortunately, I didn’t have the foresight to place any object in this photo to give an idea of how big the leaves are in comparison — they were at least two feet long and a foot wide. Talk about surface area:
Contrast this with a desert or chaparral system, in which leaves are reduced — sometimes to mere spines — and are tough, thick, and often silvery-colored to reflect the brutal, ever-present sun. Underneath an open sky free of almost any canopy cover, leaves are typically oriented so that as little plant tissue as possible is exposed to direct sunlight. Such was the case in a drier part of Costa Rica, along the Pacific Coast of the Nicoya Peninsula. The cacti and agaves tumbling onto the beach at Playa Ostional reminded me of Big Sur:
Back to the rainforest….Another common thing to see in these verdant ecosystems are lianas, or woody vines. Just think of the public transportation for Tarzan and Jane, and you’ll envision a liana. Lianas use trees as support structures to climb ever higher toward the top of the canopy where they can access the sun. In doing so, they have both good and bad effects on other species. For example, they can suppress tree regeneration or eventually drag down host trees, but they can also physically link the tree canopy together, providing easier mobility for arboreal-dwelling animals. In an article in the New York Times last May, a biologist warned that lianas may be taking over in the tropics to the detriment of trees, which are much better at storing carbon in their massive trunks than are the skinnier woody vines.
Throw a mango in the rainforest and, if you don’t hit a tree, you’ll probably strike an epiphyte. Just as the name says — epi (“upon”) phyte (“plant”), these are plants that grow on other plants. Rather than put roots in the soil, they use trunks and branches as support, deriving nutrients and moisture from the air around them (thus, another common name for them, especially at garden stores, is “air plants”). Roots are sometimes developed for better attachment. So are epiphytes parasitic, then? The typical answer is no: rather, they have a relationship with their host known as “commensalism”, in which one species benefits without having an effect, good or bad, on the other species. There is some controversy, though (a raging one, doubtless) as to whether they harm the host tree by competing for water and nutrients. the can grow quite large and eventually put stress on the tree from sheer mass. Others could argue they benefit the host by trapping water and nutrient-rich debris.
Regardless, they are important components of this ecosystem, providing shelter for insects, arachnids, and frogs to hide out, mate, bathe, and sleep in their leaves. They’re the condos of the rainforest. Lots of species in the Orchidaceae and Bromeliaceae (pineapple) families are epiphytic.
Whereas I used to compulsively turn over fern fronds to check out the pattern of spores on the underside (such as these gorgeous red ones from a post a long time ago), in the rainforest I couldn’t stop checking between the leaves of bromeliads to see if there are any animals taking up residence.
It is also common to see, or trip over, buttresses. These woody supports flanking many rainforest trees are adaptations in the root system, often seen in the ficus, or Moraceae, family. Having grotesquely expanded roots helps anchor the trees as they grow
tall, tall, taller trying to reach the top of the canopy and again, tap that elusive sunshine. Besides aiding their great heights, these trees often need extra anchorage because the soil in the rainforest kinda sucks. Yeah, contrary to popular belief — that the jungle is so full of diversity and quickly growing species because the soil is rich and filled with nutrients — the soil in the rainforest is actually quite thin and poor. The heavy duty, near constant rain causes the nutrients and humus to be continually leached out of the ground and away from the roots. Most of the minerals are stored in the insane amount of plant matter, not in the soil. Thus, buttresses serve another, related function — like arms extending out from the trunk, they collect leaf litter, creating tiny reservoirs of decomposable nutrients.
The high levels of moisture and warmth in the rainforest mean growth is on overdrive. But they also ensure that all this plant material, once dead, is recycled back into the system quickly, as well. As I used to tell kids at the Randall Museum when asking them if I could run a Costa Rican wood roach down their hands, if it weren’t for these animals’ role as “decomposers”, the planet would be buried in leaves and tree trunks and carcasses (and really, their golden wings, iridescent like soap bubbles, make these creatures — roaches, not kiddos — pretty damn beautiful). According to the University of Hawaii’s Botany department, in a tropical forest, dead organic plant matter can account for 60 tons per acre per year.
Enter fungi. With a network of mycelia spreading underground and the “fruiting reproductive bodies” of mushrooms announcing themselves above, fungi essentially eat dead organic matter, breaking down the sugars, cellulose, proteins, and etcetera other complex compounds. This both feeds the fungus and releases nutrients and minerals for use in the surrounding environment. If it weren’t for fungi, we’d be screwed, up to our suffering noses in death.
Fungi can also break down lignin, a tough, resistant compound that can only be broken down by certain species. Leftover lignin makes up the veins of leaf skeletons.
Do you have any good tropical rainforest stories, observations, or knowledge? Do tell.