Luquillo LTER 5
The Luquillo Long Term Ecological Research (LTER) Program is located in the Luquillo Experimental Forest (LEF) in northeast Puerto Rico, part of a Caribbean biodiversity hotspot. Encompassing the forests of the Luquillo Mountains and surrounding 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 characteristics of the forest and streams. By investigating the effects of these changes on animals, plants, and biological processes (nutrient cycling, food webs, carbon storage, etc.) within the forest, the Luquillo LTER supplies critical information for management and conservation of tropical forest ecosystems globally.

Hurricanes

The Luquillo LTER site was struck by Hurricane Maria on September 20, 2017, the most intense storm to strike Puerto Rico in 89 years. With  Category 4 winds on the Saffir-Simpson scale, it passed near the LTER site causing widespread defoliation and significant alteration of forest and stream structure. While some research facilities were damaged by the storm, we were able to maintain all of our on-going long-term measurements, allowing us to capture the immediate effects of the storm and showing how tree communities, animal populations, stream dynamics, and terrestrial cycling of carbon and nutrients were altered. As we continue to track the effects of the storm we are exploring which elements of the forest ecosystem are most vulnerable to severe storm damage; so far there is little evidence that the ecosystem was permanently altered by the storm, although it will continue to be a dynamic system for years to come. This is now the third and most severe storm to affect Luquillo LTER in its 30 years of operation, a rate of disturbance much higher than recorded in the previous 150 years. Thus, the Luquillo LTER provides a unique opportunity to explore how a frequent rate of hurricane disturbance can challenge the resiliency of tropical forest and stream ecosystems.

Drought

Ample evidence documents that the Luquillo Mountains, like many regions in the tropics, are changing to a drier, warmer, and more seasonal climate. In this funding cycle, LTER researchers used data and models to determine what factors control precipitation around the Luquillo Mountains with the goal of predicting future climate changes. Puerto Rico experienced a severe drought in mid 2015. Coupled with a 30% reduction in overall growth of trees, dry soils altered critical biogeochemical pathways influencing nutrient availability and the production of gases controlling the Greenhouse Effect. Streams were reduced to small pools with poor oxygen availability that were crowded with shrimp. Rain exclusion shelters over small plots were used to experimentally refine our knowledge of drought. The results improved our understanding of the effects of drying on soil processes, microbes, seedlings, and litter organisms. Additionally, collection of pre-experiment data has begun for a stream flow reduction (StreamFRE) experiment in one of the focal streams. In the future, water flow in this stream will be reduced by 50% to study the effects of increased drought on aquatic systems. Finally, we implemented a large-term project to study the effects of climate change on organisms living along a transect from the top of the Luquillo Mountains (1000 m) to around 300 m in elevation. 

Large-Scale Climate Changes Affecting the LEF

During this funding cycle, LTER researchers studied how large-scale climate changes influence rainfall variability at in the Luquillo Mountains. Utilizing historical precipitation records and regional analyses, they showed the factors associated with the driest periods, demonstrating that the early rainy season (April ? July) is responsible for ~60% of the year-to-year variability in rainfall in eastern Puerto. Building on this approach, they showed that the 2015 drought was likely caused by intrusions of hot, dry, dust-laden air arriving from Africa, a novel finding. These data are essential for predicting future forest and stream communities and their biogeochemical dynamics. We also explored long-term changes (1975 ? 2016) in cloud base height, a critical attribute of the elevation gradient in the Luquillo Mountains potentially linked to the future of endemic species located at the summits that require frequent cloud cover.

 Education and Outreach

Many graduate students (48) and undergraduate (76) students participated in the Luquillo LTER. Our Schoolyard LTER program reached 47 teachers and 410 Hispanic students in Puerto Rican schools. Since 2012, an REU program based at El Verde Field Station, and strongly connected to the LTER, has involved 48 students, 73% of whom are minorities. Our field projects have been supported by volunteer internships for recently graduated students seeking experience in tropical research. Since 2012, 70 students have participated (59% women and 37% underrepresented minorities), and many have gone on to pursue academic studies. LTER scientist Dr. Alan Covich produced a film called ?Water from the Mountain? depicting the importance of streams for biodiversity preservation and clean water for human populations.

Last Modified: 11/16/2020
Modified by: Jess K Zimmerman