Spatial variation of annual herb species in a Chilean coastal semi-desert

Background/Question/Methods

Facilitation between plants is considered to be a key process affecting the structure and dynamics of plant communities. Shrubs ameliorate the environmental stress and create favorable microclimate conditions for annual herbs growing under their canopies. However, this effect is also modified by the temporal variability in rainfall. We studied the effect of shrub Flourensia thurifera on the spatial variation of cover and density of annual herbs in north-central Chile. The aims were to assess:1) whether the F. thurifera canopies have any effect on the composition, cover and density of annual herb species, if so 2) whether the location within the canopy (close to the stem versus the canopy edge) matter. To assess the effects of canopy from soils conditions 3) we established experimental shaded plots in open spaces, and 4) plots where F. thurifera shrubs were removed. Treatments were: Open sites, with F. thurifera, shrub removed, and experimentally shaded plots. Treatments were arranged in a complete random block design. In the F. thurifera treatment data were taken close to shrub stems as well as in the canopy edges. Solar exposure of the plots (polar and equator) was recorded. Data were analyzed with canonical correspondence analysis (CAA). 

Results/Conclusions

Composition, cover and density of annual herbs species changed from the center of F. thurifera towards the open spaces. CCA analysis showed the higher eingen-values for the first axis (distance to F. thurifera stem) and the second axis (solar exposure) for both plant cover (0.19 and 0.04, respectively) and density of herbs (0.15 and 0.08, respectively). Plant cover and density values of annual herbs were highest in the open spaces and the lowest values close to the F. thurifera. Cover and density of annual plant species were lower in the equator-facing plots (p < 0.03). In 2010 (105 mm annual rainfall) we found 33 annual plant species belonging to 23 families, while in 2011 (148 mm annual rainfall) we found 38 species belonging to 25 families. Plant cover, density, and species richness of grasses were higher underneath F. thurifera than in open spaces. In open spaces the dominant species were the annual plant Erodium moschatum (Geraniaceae) and Pectocaria dimorpha (Boraginaceae). The number of native annual plant species was higher than the number of exotic species (75-79% vs. 21-25% in 2010-2011, respectively). Plant cover and density of annual plant species was lower in the shaded plots compared to open and shrub removed plots.