What do you imagine when you think of forests in the tropics? Up until now, I have always linked the idea of dense wet forests with images of thick canopies, yet this is only one aspect of tropical forests. Here at the Palo Verde National Park (PVNP) where I have been staying for the past few weeks, tropical forests look very different from the stereotyped image. Currently, it is the dry season, and while evergreen trees retain their leaves, the deciduous ones have lost theirs. It is also very hot and dry and the wind is strong. The many fallen leaves on the ground make it feel like autumn. Some of the deciduous trees have green trunks that photosynthesize while other trees have ones lined with spines and thorns.
While many people know the tropical wet forest for its biodiversity, it is also important to learn about other forest types. Dry forests in the tropics in particular represent the most endangered ecosystem in tropical regions because they are one of the most desired environments for human colonization, development and production. PVNP is special because it includes a seasonal, freshwater marsh that is an extremely important wetland area in Central America because about 60 species of resident and migratory wading birds and waterfowl use it.
I am now at a biological research station run by the Organization of Tropical Studies, volunteering as a research assistant. I am also here to learn about the story of the park. Yesterday, the former station manager, Eugenio, visited the station. He managed the station for more than fifteen years before leaving in 2008. He has a warm personality and laughed a lot during our conversation. He kindly shared with me the story of PVNP, which is the only national park that allows cattle grazing.
PVNP permits cattle grazing because of the history of the national park and also because of problems with invasive species in the park. It all began in 1920 when the land of PVNP was part of a huge cattle hacienda. In the mid-1970s the government set the land aside as Palo Verde Wildlife Refuge (PVWR). In 1998, the government recognized the importance of preserving Palo Verde as a tropical dry forest and wetland and declared it as Palo Verde National Park.
Since 1975, the wetland has changed gradually from one that has open water, low grass, and floating vegetation with some tall cattail, to one that has monotypic stands of cattail that densely occupy the wetland. The cattail not only affects other wetland plant species but has also decreased bird species richness. Managers who observed these changes suspected that the removal of cattle and the construction of a road that pushed water into the wetland could have contributed to the cattail population explosion. To control the cattail, the government decided to reintroduce cattle into the wetland.
However, the low-density cattle grazing initiative did not effectively suppress the cattail. Nonetheless, due to the historically close relationship between cattle ranchers and the land, cattle activities have not been prohibited even though cattle contribute little to curbing cattail population. Also, the cattle need the water source in PVNP, as it is scarce elsewhere outside of the Tempisque River. In fact, there are now more than 3000 grazing cattle in the greater Tempisque Basin. Eugenio commented that although cattle grazing is extremely unusual in a national park, the park and the cattle ranchers have been getting along well.