Monday, March 6, 2017

A tropical dry forest and some mangrove trees

            Again and again I find myself shocked at the diversity of Costa Rica and the ecosystems found here. Spending the last three weeks at Palo Verde National Park has allowed me to experience a tropical dry forest, a seasonal wetland, and a mangrove forest. It’s hot and dry here and to protect against water loss most trees drop all their leaves at the beginning  of the dry season. On the hikes we’ve gone on and just walking around it’s clear the vegetation here is definitely sparse in comparison to Las Cruces and Cuerici. In addition to dropping their leaves other adaptations to conserve water are peeling bark and changes in internal trunk structure to that make wood here denser. One tree we looked at would not even float in water if you threw a chunk of it in. I was surprised to learn that tropical dry forests may be the most endangered tropical ecosystems. Humans settled here because of pleasant climate, fertile, soil and dry forests are much easier to clear especially with fire during the dry season. As a result, much of the tropical dry forests have been cleared throughout Central America and protected areas are only found in Costa Rica and Mexico.
            Speaking of humans removing ecosystems, we also had the opportunity to visit and mangrove forest during our stay here. We all piled into the OTS car and drove a very long two hours out to a mangrove forest. One of the first things pointed out to us was a tree that grows in sandy areas and is probably the most dangerous tree I’ve ever heard of. It has such strong compounds that you could get a sort of acid burn from standing under it when it rains or if the wood is burned the smoke can make people blind. It has apple-like fruits that are very toxic and can be dangerous at beaches, where the tree is found, if small children are unaware of the danger. After passing that tree the mangrove forest was a welcome sight. There were almost no plants growing in the understory and small roots from the mangrove trees were popping up out of the ground everywhere. You couldn’t take step without hearing or feeling them crunch beneath your rubber boots. We later learned that these roots act as an extra respiratory system for the tree because there is little aeration in the soil making gas exchange there extremely difficult. We walked and sat on a fallen log as our professor told us about mangrove forests and encouraged us to name the differences we saw in comparison to the other forest types we’ve visited. No epiphytes, quiet and only a few species, were just a few of the observations we came up with. There are only six species of mangrove trees that make up the mangrove forest and what makes them so unique and the diversity of the forest so small is that they are able to tolerate salt water. Mangroves are found on coasts often where rivers meet with seawater. Few species are able to deal with the amount of salt which has allowed mangroves to thrive in this ecosystem with some special adaptations. Some mangroves can secrete salt from their leaves which we had the pleasure of tasting and, yes, they do taste like a salt lick.  Other mangroves will also put extra salt into old leaves that they later drop.
Being located on coasts has given mangroves many important roles in coastal ecosystems. Mangroves provide temporary (and some more permanent) habitat, shelter, and a place to find food for a variety of different organisms both aquatic and terrestrial. Mangroves also act as a filter for polluted water going down river and out to the ocean. We observed this first hand by finding all the plastic bottles and other trash that came in with the tide and got stuck in the mangroves. Mangroves are also an important barrier between lowland coasts and the ocean. They protect against erosion and severe weather. Even with the importance of these buffer ecosystems people still cut them down mostly in order to create another beak or ocean view front. In addition, human development, such as ports, have change currents and water hydrology that put the mangroves at risk. Therefore mangrove forests are another important ecosystem that needs protection just like the tropical dry forests. On our way back to the OTS car we saw large crocodiles sunning themselves on the river bank and one swimming in the river as well. It was exciting to see a larger one after having only seeing small crocodiles in the marsh at Palo Verde. Covered in mud we climbed back into the van and made a surprise trip to Pops, a local ice cream chain. It was a sweet way to end our mangroves field trip.
            As we leave Palo Verde, I will miss seeing the sunset from the boardwalk and various lookouts on limestone cliffs we climbed to. The sunsets here were probably some of the most beautiful I’ve ever seen. Palo Verde also had such active wildlife from the iguanas and Capuchins to the constantly loud howler monkeys and wandering coatis. I will not miss constantly looking out for scorpions but they were cool to see. Palo Verde is a unique ecosystem that I hope to visit again some day.

Hayley Stutzman
Macalester College.

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