Evaluating weed diversity with indices of various complexities in north-eastern Italy

Weed diversity is one of the focuses of attention of researchers, and it can be evaluated with different indices, mainly based on species richness and community evenness. In intensive cropping systems, much of the diversity is concentrated in semi-natural areas in the neighbouring habitats of arable fields. This study assessed weed diversity for seedbank and vegetation in an organically farmed valley in north-eastern Italy. Assessment was carried out with indices based on species abundance, together with Rényi diversity that also considers abundance distribution and Rao's quadratic entropy, which considers dissimilarity between species. A complete quadratic entropy approach for weeds is described. It is known that landscape context may affect community structure, and as an example of application of diversity indices in weed research, the correlation with the surrounding landscape complexity was evaluated. Results show that a community can be relatively balanced with even just a few species. With diversity indices based on species abundance only, it is therefore difficult to quantify balance. The Rényi diversity can overcome this limit, and the quadratic entropy can isolate extreme communities. In conclusion, the diversity of a weed community can be better evaluated using more diversity indexes, and the quadratic entropy can provide new criteria for ranking the diversity and combine a number of traits into a single numerical descriptor. The correlation between landscape complexity and weed diversity is low but confirms that agro-environmental schemes should consider the management of fields and landscape together.