Species diversity of plant communities in contrasting landscapes of the Rolling Pampa (Argentina)

POGGIO, SANTIAGO L; GHERSA, CLAUDIO M

Hamar, Noruega

Congreso; 14th European Weed Research Society Symposium; 2007

European Weed Research Society

<!-- /* Style Definitions */ p.MsoNormal, li.MsoNormal, div.MsoNormal {mso-style-parent:""; margin:0cm; margin-bottom:.0001pt; mso-pagination:widow-orphan; font-size:12.0pt; font-family:"Times New Roman"; mso-fareast-font-family:"Times New Roman"; mso-ansi-language:EN-US; mso-fareast-language:EN-US;} @page Section1 {size:612.0pt 792.0pt; margin:70.85pt 3.0cm 70.85pt 3.0cm; mso-header-margin:36.0pt; mso-footer-margin:36.0pt; mso-paper-source:0;} div.Section1 {page:Section1;} --> <!-- /* Style Definitions */ p.MsoNormal, li.MsoNormal, div.MsoNormal {mso-style-parent:""; margin:0cm; margin-bottom:.0001pt; mso-pagination:widow-orphan; font-size:12.0pt; font-family:"Times New Roman"; mso-fareast-font-family:"Times New Roman"; mso-ansi-language:EN-US; mso-fareast-language:EN-US;} @page Section1 {size:612.0pt 792.0pt; margin:70.85pt 3.0cm 70.85pt 3.0cm; mso-header-margin:36.0pt; mso-footer-margin:36.0pt; mso-paper-source:0;} div.Section1 {page:Section1;} --> Diversity of plant communities, as accounted by the number of species, is determined by factors operating at different scales. Effects of competition and disturbance on the richness of plant communities are well understood, while determinants acting at the landscape and regional scales are less known. Therefore, our aim was to explore the relationships between: (1) species diversity and landscape heterogeneity; and (2) local (α), turnover (β), and landscape (γ) diversities in weed communities. Plant species richness was sampled in field habitats cropped with cool- (wheat and pea) and warm-season crops (maize and soybean). Landscapes, fields, and field habitats (fence-row, field edge, and field centre) were hierarchically nested to compare α-, β-, and g-diversity. Percent of cropland in the landscapes was chosen as a straightforward indicator of heterogeneity, because it was negatively correlated with the Simpson diversity index (Gini coefficient, 1 - <!-- /* Style Definitions */ p.MsoNormal, li.MsoNormal, div.MsoNormal {mso-style-parent:""; margin:0cm; margin-bottom:.0001pt; mso-pagination:widow-orphan; font-size:12.0pt; font-family:"Times New Roman"; mso-fareast-font-family:"Times New Roman"; mso-ansi-language:EN-US; mso-fareast-language:EN-US;} @page Section1 {size:612.0pt 792.0pt; margin:70.85pt 3.0cm 70.85pt 3.0cm; mso-header-margin:36.0pt; mso-footer-margin:36.0pt; mso-paper-source:0;} div.Section1 {page:Section1;} --> Ψ) of the land uses in a landscape. Species diversity was additively partitioned into its a-, β-, and γ-diversity components, calculating β-diversity as the difference between g-diversity and mean α-diversity. Total species richness was 222. Regardless of the cropping season, γ-diversity decreased as the proportion of cropland in a landscape increased. Within each landscape, fence-row habitats had the highest γ-diversity values, which increased with landscape complexity level. Since α-diversity did not significantly differ between crops and landscapes in each field habitat, β-diversity reflects the variation of community composition among the fields in a landscape, as a result of the landscape complexity. Fence-rows β-diversity had the highest relative contribution of total species richness, being ca. 40% in cool- and ca. 36% in warm-season crops. Field edges β-diversity was significantly higher in pea than in wheat and in maize than in soybean. β-diversity of field centres was higher in pea than in wheat crops, whereas there were not significant differences between the warm-season crops. Variation of the inner field β-diversity in pea and maize indicates that mass effects from field margins are involved in maintaining the species richness of weed communities. Plant diversity of agricultural landscape could be enhanced not only by maintaining highly diverse non-cropped areas, but also by increasing the richness of crop species (i.e. growing crops differing in growing cycle and ground-cover dynamics).