When the rainforest dries

The amount of rain that some tropical regions receive can be impressive.  The forest around El Verde Field Station in Puerto Rico, our long-term study site, receives around 3.5 m of rainfall a year.  However, during 2015 the entire Caribbean region experienced a strong drought and we recorded a little over 2 m of rain at El Verde. 

Quebrada Prieta - El Verde

Map of our long-term study site in the Luquillo Experimental Forest. 

The drought of 2015 was the most severe drought in the last 5 decades in this tropical rainforest. Flowing streams became series of isolated pools.  Water limited riparian vegetation dropped large amounts of leaf litter into the stream.  During the peak of the drought all parts of the ecosystem were affected by the lack of water. 

Prieta stream, during an average year (top) and during the 2015 drought (bottom). 

Photos: Pablo Gutiérrez

Our latest publication describes the effects of the 2015 drought on multiple components of the ecosystem.  Our main findings include:

• Streams became a series of disconnected pools with different physicochemical characteristics.
• Inputs of riparian litter peaked early during drought and accumulated in pools due to the lack of flow
• Dissolved oxygen fluctuated during the day and pools became anoxic at night
• Small macroinvertebrates (not shrimp) increased in numbers after shrimp moved to larger pools.   Only tolerant taxa were able to deal with the lack of oxygen.

Our findings provide valuable information on how rainforest streams respond to drought.  This information is particularly important when one considers that climate change models predict an increase in drought frequency for the Caribbean and other many regions of the tropics.

Our publication will appear in the June issue of the journal Freshwater Science.

Gutiérrez-Fonseca, P. E., Ramírez, A., Pringle, C. M., Torres, P. J., McDowell, W. H., Covich, A., Todd Crowl,  & Pérez-Reyes, O. (2020). When the rainforest dries: Drought effects on a montane tropical stream ecosystem in Puerto Rico. Freshwater Science, 39(2).  Link to FWS.