Deforestation reduces the genetic structure of an epiphytic weed across space and time: an IBM approach

Deforestation has allowed the massive dispersal and reproduction of some plants that are commonly referred to as weeds. The rapid spread of many weeds into newly disturbed landscapes is often boosted by clonal growth and self-fertilization strategies, which conversely increases the spatial genetic structure (SGS) of populations and reduces the genetic diversity. Here, we use empirical and modeling approaches to evaluate the spatio-temporal SGS dynamics of Tillandsia recurvata (L.) L., a common epiphytic weed with selfing reproduction and clonal growth widespread in dry forests and anthropically deforested landscapes in North and South America. We constructed an individual-based model (IBM) and adjusted the parameters according to empirical genetic data, to simulate the spreading of T. recurvata over time and across random landscapes with distinct tree densities. From empirical data, we observed a strong SGS among T. recurvata subpopulations hosted on neighbor trees and a contemporary spread from several population sources. Our model shows that the highest SGS appear in landscapes with more than 200 trees/ha and up to the 5th year of colonization of open landscapes (ca. 100 trees/ha) when SGS starts to reduce drastically. These results suggest that the deforestation commonly observed in anthropically transformed landscapes may reduce the dispersal limitation and genetic structure of T. recurvata subpopulations, creating suitable conditions for the rapid spread of T. recurvata from multiple surrounding sources. The combination of clonal growth and self-fertilization with the optimal conditions created by anthropogenic transformations may explain the spreading success of T. recurvata and other weeds into new landscapes. Our results indicate that the drastic reductions in tree densities induced by human-modifications in natural landscapes may lead to a partial loss of resistance for dispersal by wind and increased the conditions for T. recurvata to develop massive populations in anthropogenic landscapes.