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The Costa Rican ForestsMaster Gardener Scoop – March 16, 2016

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The Costa Rican Forests

Dr. Jeanette M. Endres, Master Gardener

Recently, I visited Costa Rica and experienced one of the most fantastic places on earth that displays immense biodiversity. I had the opportunity to take a guided tour of the rainforest and was surprised to learn that there are actually three types of rainforest.  The guide pointed out that although the tropical rain forest is the one that most tourists want to visit, we should consider that the cloud forest and tropical dry forest are additional types of rainforest. We were told it was the dry season until May.  However, the day we visited the tropical rainforest, it rained and rained but only in the rainforest. It did not rain anywhere else. We were told that an annual rainfall of at least 100 inches per year in the rainforest was likely.   

The rainforest we visited was in the southwest part of Costa Rica. We observed tall trees and looping vines which are called lianas. Temperatures were warm, hovering around 90 degrees with high humidity. We were informed that scientists have estimated that more than half of the entire world's plant and animal species live in rainforests and that seventy percent of the plants in the rainforests are trees. We observed that many of the trees have straight trunks that don't branch out.  This is because there is no need for the trees to grow branches below the canopy where there is little light.

Our guide told us that there are four distinct layers of trees in a rainforest. There are emergent trees which are spaced wide apart with umbrella-shaped canopies. The upper canopy allows some light to filter through at the top of this layer.  Due to this light, this is where most of the rainforest animals make their homes. The lower canopy or understory is comprised of the trunks that come from the canopy trees. Trees seldom grow over twelve feet high here due to the lack of light. There is little air movement, and the humidity is very high. A few forest animals make their home in this layer, but the forest floor is completely shaded so few plants or animals can survive there.

We observed a cloud forest from a distance while traveling with our tour group. The fog was hovering over the high slopes of the mountains. According to our guide, the cloud forest is characterized by a continuous low-level cloud cover which is usually at the upper canopy level above the tree line.  The cloud forest covers the higher slopes of volcanoes and mountains across Costa Rica. The sun has a hard time breaking through this thick veil of clouds, causing a slower rate of evaporation, and thus provides the plants with life-giving moisture.  

The guide showed examples of what are called epiphyte plants.  Epiphytes are plants such as lichens, orchids, and bromeliads that grow on other plants or trees non-parasitically. They live by collecting their moisture and nutrients from the air, rain and debris that surround them.

We visited the tropical dry forests during the dry period.  We had no rain during our entire 14-day stay in Costa Rica, despite the fact that it had rained during our rainforest tour.  We could drive through part of a tropical dry forest since some of the land has been claimed for grazing. Due to the lack of rainfall, there are near drought conditions in this area.  Since the undergrowth is so dense and tangled due to light penetration, a variety of plants that love these conditions tend to thrive.  The trees also have thicker bark and deeper roots to help them withstand these conditions.