Luquillo LTER 5
The Luquillo Long Term Ecological Research (LTER) Program is located in northeast Puerto Rico, part of a  Caribbean biodiversity hotspot. Encompassing the Luquillo Mountains and surrounding urban and developed areas, the goal of the Luquillo LTER program is to determine how changing climate and disturbances (hurricanes, land use, drought, etc.) drive changes in the forest. By investigating the impacts of these changes on animals, plants, and biological processes (nutrient cycling, food webs, carbon storage, etc.) within the forest, Luquillo LTER research supplies critical information for management and conservation of tropical forest ecosystems globally. During the funding period for LTER 5 (Jan 1, 2015-Dec 31, 2016), the program focused on the effects of climate change, specifically the impacts of more frequent droughts and hurricanes, on the structure and function of tropical forest ecosystems. 

Climate
Ample evidence documents that the Luquillo Mountains, like many regions in the tropics, are

changing to a drier, warmer, and more seasonal ecosystem. Models predict a significant increase in extreme storm events, combined with longer and more frequent periods of drought. Understanding how these changes are affecting the Luquillo Mountains is a core goal of Luquillo LTER. In this funding cycle, researchers used data and models to determine what factors control precipitation around the Luquillo Mountains (wind, moisture, pressure, etc.); knowledge of how climate, affects ecosystem function can help predict the effects of future climate changes. To further explore this topic, we began implementation of a large-scale project to study the effects of climate change on organisms along a transect from the top of the Luquillo Mountains (1000 m) to around 300 m in elevation. Theory predicts that tropical organisms will respond more strongly to environmental changes along elevation gradients, where climate varies in space,  compared to organisms in uniform climates. These responses may provide an early indication of what the future holds for many of the world’s ecosystems.

Drought
Puerto Rico experienced a severe drought in 2015, the strongest since 1994.  We were able to compare patterns of rainfall, soil moisture, and stream flow during 2015 with long-term averages using LTER data. Soil moisture and stream flow were reduced during the drought period (April-August 2015). A period of high litterfall was recorded early in the drought, and there was a 30% reduction in overall growth of trees. Increased sampling in two of our focal streams revealed several small pools, or “refugia,” that remained where high densities of shrimp were found.  

Several projects are currently underway to more thoroughly investigate the effects of increased drought on the forest. A throughfall exclusion experiment (TEE), consisting of rain exclusion shelters that will reduce soil moisture in small plots in the forest, will be used to determine the impact of multiple short-term droughts on soil as well as on microbes, seedlings, and litter organisms. Additionally, collection of pre-experiment data has begun for a stream flow reduction experiment (StreamFRE) in one of the focal streams. In the future, water flow in this stream will be reduced by 50% to study the impacts of increased drought to aquatic systems, as well as identify any related impacts to terrestrial systems.

Hurricanes
In 2014 we conducted a second trim of our Canopy Trimming Experiment (CTE) plots to simulate the impact of more frequent hurricane disturbance on the forest. Post-trim sampling of soil, microbes, groundwater, vegetation, and insects continued during this funding period. The green leaf litter deposited on the forest floor caused a peak in nutrients leaching into the soil and groundwater 5 weeks after the trim. Bacterial and fungal communities were also significantly different between the trimmed and control plots. The abundance of shade intolerant (or “pioneer”) plants increased in the trimmed plots, compared to the slower growing, shade tolerant species that dominate undisturbed forest. An increased frequency of hurricanes would result in forests dominated by pioneer species. This change in species composition, in turn, will have cascading effects on streams, fauna, and biological processes important to ecosystems such as their ability to store carbon. 

Education and outreach
The LTER Schoolyard staff conducted field workshops for 80 public school students, ranging from middle to high school, in Puerto Rico. The workshops covered vegetation, river ecology and soil characterization at El Verde Field Station. Students participated in data collection and entry, as well as analysis methods for each of the different focal areas. Additionally, 20 science teachers from the Puerto Rico private and public school sectors participated in a Data Jam Workshop designed to investigate a basic ecology question and develop a claim-evidence-reasoning presentation to demonstrate their findings. We continued to participate in the Research Experience for Undergraduates (REU) program, a summer program designed to allow students from small institutions to design and conduct their own field research project. Over 700 students applied and sixteen were chosen

Last Modified: 03/27/2017
Modified by: Jess K Zimmerman