Tropical ash (Fraxinus udhei) invading Andean forest remnants in Northern South America

Exotic invasive species represent a major driver of the loss of biological diversity and services provided by ecosystems globally. An important source of species becoming invasive are the commercial afforestation projects using fast growing and adaptable exotic species, which may become invasive impacting natural environments. The Tropical Ash ( Fraxinus uhdei ) native to México has been widely introduced for many decades to Colombia and other countries for timber, live fences and urban greening, is now common in many areas of the tropical mountains, and has been observed expanding into native forests in Colombia. This study explores the invasion of Tropical Ash in remnant Andean forests in Colombia, to understand the invasion pattern and the demographic structure of Tropical Ash. The analysis took into account biotic and physical factors, such as distance to the propagule source, vegetation cover types, and density of the understory and canopy cover. Although the reproductive strategy of the Tropical Ash is of “r” type with low survival rates, the results show evidence for an active process of invasion characterized by an aggregated distribution pattern. The study shows the existence of an interaction between the distance to the propagule source and the vegetation cover, which has an additive effect on the demographic structure of the population.