# High Propagule Pressure and Patchy Biotic Resistance Control the Local Invasion Process of the Tree Ligustrum lucidum in a Subtropical Forest of Uruguay

## TL;DR

This study explores how the invasive tree Ligustrum lucidum spreads in a Uruguayan forest, finding that seed dispersal and local resistance from certain tree species limit its spread.

## Contribution

The study identifies specific biotic resistance mechanisms and spatial patterns of invasion by L. lucidum in a subtropical forest.

## Key findings

- Ligustrum lucidum propagule pressure is highest near mother trees and 100-1000 times higher than other species.
- Jodina rhombifolia forest stands show lower L. lucidum survival due to biotic resistance mechanisms.
- Local spread of L. lucidum is controlled by dispersal patterns and patchy resistance from native species.

## Abstract

The tree Ligustrum lucidum (W. T. Aiton, Oleaceae), native to East Asia (China), has become an aggressive invader of subtropical and temperate forests around the world. To understand how its local small-scale spread is controlled, we studied (48 plots of 4 m−2), in a subtropical forest of Uruguay, the distribution and survival of seedlings, saplings, and poles to assess the effects of dispersal from mother trees (distance), microsite type (forest stands defined by dominant species), and past control measures. The propagule pressure of L. lucidum, estimated through seedlings density, was between 100 and 1000 times higher than that of other species of the community and was concentrated around mother trees (<10 m of distance). Spatial variability of seedlings, saplings, and poles densities were explained by the interaction between distance to mother trees and forest stands. Significative lower densities were observed in the forest patches (stands) dominated by Jodina rhombifolia, and a field survival experiment confirmed lower survival of poles at Jodina stands, demonstrating that some resistance mechanism is operating there. We propose two biotic mechanisms of resistance: herbaceous competition and/or roots hemiparasitism by J. rhombifolia, reducing seedling and sapling survival. We concluded that a high propagule pressure, small-scale dispersal from mother trees, and patchy biotic resistance at Jodina stands control the local spread and domination process of the tree L. lucidum in the studied forest.