by Suzanna Engman
photos by José V. Camacho

The sound of hiking boots on rocks and dry dirt, the ceaseless wind, and the sauna-like dry heat evokes the landscape of the southwestern United States. Without the sea crashing against the shore and the salt spray, one could be in Arizona or New Mexico. But it is the wind and the salt that have helped to shape the unique landscape of Guánica Dry Forest Reserve. Some of the same tree and bush species also grow in El Yunque Rainforest, about a two hour drive northeast of Guánica, but in the coastal plateau of the Guánica forest they are smaller, scarcer, and, . . . well, . . . windswept.

Perched atop the Guánica cliffs with a steep vertical drop to the Caribbean Sea, gnarled dwarf trees dot the landscape like tiny islands of wind-bent vegetation. Salt dried on their leaves can be tasted if licked, and underneath the sparse shade they provide live unseen populations of arthropods. Many of the arthropods that make up the soil fauna under these trees—scorpions, spiders, beetles, for example—must be identified under a microscope. It is nothing short of miraculous that this desert refuge, with only sunshine, limestone, and occasional bouts of rain to support it, teems with so many life forms.

One-third the size of El Yunque, Guánica’s four thousand hectares of forest is home to twice the number of plant species as the rain forest and nearly 140 species of birds, half the number of bird types found on the island. The biodiversity of this dry forest and the rain forest make Puerto Rico a biodiversiry hotspot. Guánica receives only 860 millimeters of rain a year—compared with the 3,060 millimeters a year of the rain forest. The 550 species of plants that grow in Guánica are amongst the toughest around. In the dry season between December and April, many trees in Guánica drop their leaves, which provide the necessary resources to support the life that thrives under their branches.

One of the questions that CATEC has investigated, whether litter arthropod communities vary among plant species, was answered by María Fernanda Barberena’s CATEC-sponsored research for her dissertation, “Tree Species Effect on Soil Arthropod Diversity and Dynamics in the Guánica Dry Forest.” Her research focused on the communities of arthropods under five species of trees in Guánica. Two of the five species, Conocarpus erectus (button mangrove) and Cocoloba uvifera (sea grape) grow only in coastal areas, while Ficus citrifolia (strangler fig) and Tabebuia heterophylla (white cedar) are also found in the rain forest, where they grow larger. The other species, Pisonia Albida (corcho bobo), is endemic to dry forests. The lives of the microscopic arthropod communities depend entirely on the lone tree that provides their habitat.

Biosphere Reserves A biosphere reserve is an area of high biodiversity designated as such by UNESCO. About five hundred biospheres exist in a hundred countries. Two are located in Puerto Rico: the El Yunque Rainforest and the Guánica Dry Forest. UNESCO’s “Man and the Biosphere” program began in 1970 to preserve biodiversity while promoting sustainable use of natural areas around the world. Biospheres are intended to conserve landscapes, ecosystems, and biodiversity. They also serve to foster socio-cultural and ecologically sustainable economic development. A third function of a biosphere is to support research, monitoring, and information exchange about conservation and development. http://www.unesco.org/mab/mabProg.shtml

Barberena’s research reveals that average abundance, or the number of individuals, of arthropods is similar among the five plant species, but arthropod richness, or the number of species, was highest in Pisonia and Ficus. Arthropod species composition, identity of arthropod species, is different among plant species and among the different litter layers under the trees; and the more decomposed layers harbored higher abundance and richness of arthropods than the less decomposed layers. Barberena also found that the identity of arthropod species was different among all litter layers. In addition, the nutritional content of the litter was measured as nitrogen concentration, which was highest in Pisonia and lowest in Conocarpus, and as phosphorus concentration, which was similar across species. However, the relative abundance of phosphorus to nitrogen was similarly low in both species.

Previous researchers found that dry forests follow a pulsing dynamic. In other words, an increase in water triggers biological activity. For example, during the dry season the leaves fall off the trees and decomposition decelerates, resulting in the accumulation of organic matter. But when the rainy season begins, the water triggers biological activity that results in an increase in decomposition. Barberena found a similar pattern in arthropods because in the wet season arthropod abundance and richness increased. These data led Barberena to conclude that the decrease in arthropods during the dry season and the increase in the wet season were best explained by the arthropod life cycle and the availability of life-sustaining resources.

So what happens to the dry forest and the arthropod communities under them if it becomes drier, as climate-change models predict? That is a question CATEC researchers are currently working to answer.

Yogani Govender uses a PDA to download environmental data from dataloggers.

Yogani Govender

Uncovering the mystery of Guánica Forest Reserve’s ecohydrology is postdoctoral researcher Yogani Govender’s question in the Ecosystem Process and Functioning area of CATEC. According to climate models, the climate of the earth is going to become drier, and it is suspected that the first ecosystems lost will be dry forests, as they are already living under extreme conditions. The CATEC scientists are investigating how plants in dry forests partition water use during different times of the year. Govender explains, “We want to understand where plants obtain their water during extreme dry conditions. Is it from underground water? Do they store water in their roots? Is there water stored in the soil?” Govender and other investigators will be looking at how the plants adapt physiologically to the changes in the availability of water.

“The nice thing about working in Guánica is that it’s a unique ecosystem. Plants establish themselves in an area that’s rocky with little or no soils, experience erratic rainfall, and extremes in temperature. Each plant forms its own island of leaf litter and organic matter, creating its own microclimate.”

The dry forest is a very different ecosystem from the marine environment around it. When Govender, a graduate of the doctoral program in biology at the University of Puerto Rico, Ro Piedras, first began her studies here, she had envisioned herself working with coral reefs but soon after discovered that she suffers from diving panic—a common disorder amongst scuba divers in which the dive induces a panic attack—and had to rethink her options. In addition, a South Africa native, Govender had to learn Spanish because her first biology classes were in Spanish. She attributes her survival as a graduate student in part to support from professors and fellow students. One month prior to starting the graduate program, she was matched with another graduate student who helped with orientation, obtaining a social security card, and other practical matters. The university trained Govender to become a teaching assistant in General Biology and Human Biology, and other graduate students helped her to learn Spanish.

Before she started graduate studies, Govender was a high school biology teacher in South Africa. She earned her master’s on a UNESCO scholarship that was awarded to the University of Zululand to advance higher education research in black universities. Her research helped assess potential development as a means to improve community economy in Mabibi, a rural area in South Africa. She was a member of a multidisciplinary team that included botanists, entomologists, climatologists, soil scientists, water quality specialists, agronomists, and geographers. Govender analyzed soil nutrients, water quality, and biodiversity. She also assessed the community’s needs and use of natural resources. The project culminated in a successful agriculture project and an ecotourist lodge.

As a doctoral student, Govender and her advisor, Alberto Sabat, Ph.D., developed a multidisciplinary project to study population declines in Puerto Rico of Cardisoma guanhumi, a land crab known here as juey comun. Govender researched how crab size has declined over time, using Geographic Information Systems to understand how land-use changes have affected the distribution of land crabs. “Coming from a geography background, I wanted to incorporate social aspects,” she recalls. “Besides just looking at the population biology of the crab, I also looked at the history of the land crab fishery, crab hunters’ perceptions and attitudes towards population declines, and the current management plan in Puerto Rico.”

Govender divided her time between studying the ecology of the crab and interviewing crab hunters. She learned that crab hunters were aware that the Department of Natural and Environmental Resources (DRNA by its Spanish acronym) regulates crab hunting but unaware of the specifications and the reasoning behind the regulations. “Only one or two crab hunters actually saw the piece of paper with the DRNA regulations for crab hunting.” One thing that concerns Govender is the lack of concern for declining numbers of land crabs in Puerto Rico. “There are no education outreach programs to provide crab hunters and public with management information for Cardisoma guanhumi. Currently, the crab festival in Maunabo takes places in July, the period when land crab capture is prohibited by the DRNA regulations,” she says. “And even though land crab populations have declined, no measures have been taken to protect land crab habitat in Puerto Rico.”

Three years of Govender’s doctoral research was supported by a NOAA Graduate Research Fellowship that was awared for her work in the Jobos Bay Reserve. “I learned about making grant applications and developing a budget. I was lucky to have been in charge of my own scholarship, budgeting funds for buying equipment and materials, sending samples to be analyzed and traveling to scientific meetings. A fellowship allowed me to to understand the research funding process.”

Govender sifts through a handful of soil from under a Guánica Dry Forest dwarf tree. Fine roots of the tree disappear when the soil is drier. CATEC scientists collect soil samples for soil moisture and nutrient analysis.