Exotic tropical pine forest impacts on rainfall interception: Canopy, understory, and litter

Tropical forests have experienced rapid deforestation due to demand from agriculture, timber, and urbanisation. Throughout the Caribbean, planting resilient, fast growing exotic pine trees such as Pinus Caribaea or Pinus Oorcarpa have been used to reforest many degraded landscapes. However, little is understood on how these exotic pine forests alter hydrological processes and water resource availability. We examined the rainfall interception dynamics between an exotic pine and contiguous native secondary forest in Trinidad. Canopy, understory, and litter interception were quantified and examined along with throughfall variability, rainfall characteristics and canopy cover. Our results indicate that over a one-year period, the exotic pine forest intercepts 30% more of the incoming precipitation than the native forest, reducing the rainfall reaching the forest floor. The pine forest had a lower canopy cover but still had a higher storage capacity of 4.3 mm, leading to a higher annual interception of 29%. The native forest had a lower storage capacity of 2.6 mm and a lower annual interception of 24%. Understory vegetation played a critical role in the interception process in the pine forest storing an additional 29% of incoming rainfall increasing the total vegetative interception in the pine forest to 58% (763 mm). These findings point to the creation of drier conditions within pine forest and the need to re-examine the use of pine trees as a reforestation tool. This study highlights the importance of understory vegetation interception and stresses the need for more research on understory-precipitation interactions.