Factors shaping alien plant species richness spatial patterns across Natura 2000 Special Areas of Conservation of Greece

- A positive native-alien plant species richness relationship was observed.
- Fewer aliens were found in steep, high-elevated and distant from water-bodies areas.
- Most aliens were found in distances less than 20 km from the road network.
- Human population density had a positive effect on alien plants occurrence.
- All factors are linked to propagule pressure, which is driven by human presence.

This paper aims to determine the main factors that shape the spatial patterns of alien plant species occurrence across Natura 2000 Special Areas of Conservation (SACs) in Greece, and quantify their influence. A series of spatial analysis techniques for the development of a spatial database of the factors involved, followed by a boosted negative binomial Generalised Additive Model for location scale and shape, were implemented. Native plant species richness, topography and hydrography, human population density, and a spatial preference to the northern-western sites are the key factors that explain the variation in the occurrence of alien plant species. Native plant species richness and human population density have a positive effect on alien plant species presence, while topography aspects, such as elevation and slope, and the distance from the hydrographical network a negative one. All factors are indirectly linked to propagule pressure emphasizing the importance of human activities for the efforts on managing protected areas.

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