Nature, Opinion

The Guanacaste forest where water comes from

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We are hanging about 20 meters (65 feet) from the ground. The wind is constantly moving the trunk of the tree from which we’re hanging, and the branches emit a muffled moan, giving way to the movement.

I have experience working at heights, but trees are something else. They’re alive and they react to their surroundings. These trees, populated by epiphytes and mosses, are like a forest above the forest, a place protected by height that’s rarely accessible.

Epiphytes are plants that grow on other plants, but without being parasitic to the one that supports it in terms of nutrition. Stated more clearly, they develop on other plant species but do not feed on them.

We don’t associate Guanacaste with the cloud forest, but we are within the borders of the province, in an environment that has nothing to do with the pampas and the dry forest. Here, in the highlands between Abangares and Tilarán, Dr. Sybil Gotsch (from the University of Kentucky) is conducting an experiment to understand the relationships between epiphytes, their host trees,and the water cycle.

My role is merely documentary.  I’m photographing and making a video about the different research processes. We’re working with funds from the National Science Foundation in the United States, as well as with support from several universities. Dr. Gotsch considers it essential to produce materials that make it possible to communicate the scope of the experiment.

We track a total of 20 trees, some in grassy areas, others in the forest. Half of them are control subjects that haven’t had much human intervention other than the placement of sensors; the remaining 10 have been stripped of the layers of epiphytes that covered their branches.

The intention is to understand what effect an eventual disappearance of epiphyte species might have on the trees of the cloud forest, as a result of climate changes. This implies understanding many interrelationships that sometimes aren’t so clear to us, from the real importance of epiphytes to the reasons why we have drought in the mountains.

The first objective is to demystify these plants. Many of us have grown up with the idea that they grow on trees by parasitic force, and there are even those who assume that keeping trees free of lichens and moss is a way to guarantee their health. The reality is that there are several forms of coexistence between trees and their hosts, which even experience mutualism.

The second objective is to understand the water cycle in depth. Dr. Gotsch explains to me that the cloud forest can be understood as a sponge.

Dr. Sybil Gotsch directs activities in the treetops.Photo: José Pablo Porras Monge

Here the dynamics are much slower than in the lowlands. The organic components that fall to the ground take longer to decompose, increasing the soil’s capacity to absorb water. Add to this the fact that the epiphytes increase the forest’s biomass, helping to capture more water, which ends up accumulating in the soil.

All this implies that the water resource begins in the mountains. There, the captured water feeds the streams. In the absence of forests, the water would run directly to the rivers, and from there, to the ocean. There would be no reserve storage, as is normally the case.

The hypothesis of this research high up in these giants of the forest is that without epiphytes, we would lose an important capacity for storing water. Our water resource “savings account” would drain, to use a metaphor.

That’s why we’ve installed different devices in the trees being studied: transpiration and sap flow sensors in the trunk and temperature and humidity sensors in the epiphyte mats, as well as mini weather stations in the treetops, to measure relative humidity, solar radiation and wind speed, among other factors.

Installation operations and sensor functioning.Photo: José Pablo Porras Monge

Different sensors and data collection systems installed high up in a tree.Photo: José Pablo Porras Monge

The effects that they expect to record range from a variation in soil moisture under the tree to an increase in wind speed, because the epiphytes could function as windbreaks and even give the tree structural strength.

Dr. Gotsch explains this to me in more detail:

There’s a deep-rooted idea that epiphytes are bad for the tree. We’ve discovered that many times, half of a tree’s structure has been made up of epiphytes. This implies some kind of structural relationship.”

Along the same lines, the research team hopes to verify that the epiphytes play a positive role for the tree, helping to keep it cool by accumulating moisture and even providing nutrients to the soil.

Could they even help the tree in stressful situations?

Dr. Gotsch tells me about documented cases in the Atacama desert, where this relationship has been seen between a certain type of cacti and these plants. The possibility of this occurring in the cloud forest remains to be seen.

Here, hanging from a rope, I see first-hand what is sensed intuitively from the ground: the epiphytes literally constitute a hanging garden. It would be strange if there wasn’t a significant contribution from these systems to the forest capturing water.

The problem is that we are talking about extremely delicate systems. The “soil” on which the epiphytes grow, up high, is a composition of organic matter and sparse mineral components. It is even debated whether it should be considered “soil.” They are thick mats of roots, leaves and soil particles carried by the wind.

Costa Rican arborist Keylor Muñoz installs a micro climate station.Photo: José Pablo Porras Monge

In the 1990s, in this same study area, Dr. Nalini Nadkarni removed fragments of these mats to determine their recovery speed. Almost 30 years later, they haven’t been fully reestablished.

This is concerning. Today, we’re certain of the change in the planet’s temperatures and climatic processes. This implies that the forest is also going to change, directly affecting the ability to capture water in the soil and therefore the availability of water resources.

Is it possible to compensate for these changes?

Dr. Gotsch doesn’t seem pessimistic. She believes that we can focus our efforts on having more forests, protecting what we have and practicing responsible livestock management. The latter needs to be done hand in hand with economic diversification in areas that have traditionally depended on this activity, as well as monocultures.

I sit on my harness and let the wind lull me to sleep. Many years ago, while walking through another cloud forest, my partner pointed out that the trees in the mist looked like dancers holding a position. Today I feel like I’m dancing among the branches of these giants. Sometimes it seems like I hear the whisper of the plant life that shapes this kingdom on high.


José Pablo Porras Monge is a photographer, documentary film director and writer based in La Sierra de Abangares. If you are interested in following the research, you can visit: You can also see more images and read some personal reflections at Imá