Tropical dry forests on serpentine soils are structured by cloud line: Insights from plant functional diversity and turnover across elevation
Originating as an island in the Pacific Ocean, Peninsula de Santa Elena is an ancient serpentine formation located in one of the driest areas of Costa Rica. At its highest elevations Santa Elena is blanketed by clouds making it one of the most unique tropical dry forest ecosystems in the world. Based on historical aerial photographs and oral history, the presence of clouds and the lowest elevation at which clouds form has decreased within the past 50 years due to a drier, warmer climate. How does the presence of clouds structure a dry forest plant community and can functional diversity and turnover reveal whether and how much cloud line has receded in recent history? This study provides the first systematic inventory of plant diversity, abundance, and function across a short but steep elevational gradient (0-720m a.s.l.) in Peninsula de Santa Elena, Area de Conservación Guanacaste.
Taxonomic diversity was lower for tropical dry forests on serpentine soils compared to nearby tropical dry forests on volcanic soils while functional diversity was comparable. Further, intraspecific plant trait variation was higher on serpentine compared to volcanic soils which helps to explain wider elevational ranges compared to species found on volcanic soils. Finally, functional diversity and turnover of herbaceous and woody plant species point to a receding cloud line in recent history. Functional turnover was greatest at lower elevations for woody plants, at intermediate elevations for herbaceous plants and at the highest elevations for epiphytes, mosses, and ferns. Continued recession of the cloud line will likely lead to the eventual disappearance of this unique and unexplored ecosystem.