Field boundary effects on soil seed banks and weed vegetation distribution in an arable field without weed control (Vaucluse, France)

Studies on the distribution of arable weed species relative to the field boundary have already been performed, although most of these studies have been realised in north-western Europe on intensively managed arable fields. Nevertheless, it is important to examine arable weed communities in more extensive cropping systems to increase our knowledge on how arable plant communities are constructed. Plant composition and seed bank of an arable weed community were sampled in an arable wheat field in Vaucluse (south-eastern France) at 1-m intervals along five 25-m perpendicular transects from the herbaceous field boundary. The results showed that seed bank distribution and plant composition are primarily influenced by distance from the field boundary in the crop edge rather than soil characteristics or wheat density. (© 1999 Inra/Éditions scientifiques et médicales Elsevier SAS.)Effets de la lisière sur la distribution du stock semencier et des mauvaises herbes d'un champ cultivé sans désherbage (Vaucluse, France). De nombreuses études ont été réalisées sur la distribution des mauvaises herbes en relation avec la lisière du champ mais la plupart de ces travaux ont été menés dans les cultures intensives du nord-ouest de l'Europe. Cependant, il est également important d'étudier les communautés de mauvaises herbes dans des écosystèmes cultivés plus extensivement afin d'accroître nos connaissances sur les modalités de mise en place de ces communautés. La végétation et le stock semencier d'une communauté de mauvaises herbes ont été échantillonnés dans un champ de blé du département de Vaucluse (sud-est de la France) tous les mètres le long de cinq transects perpendiculaires à une lisière herbacée. Les résultats montrent que, dans les premiers mètres en bordure du champ, la distribution du stock semencier et la composition botanique sont en premier lieu influencées par la distance à la lisière herbacée plutôt que par les caractéristiques du sol ou la densité de blé. (© 1999 Inra/Éditions scientifiques et médicales Elsevier SAS.

Assessing allometric models to predict vegetative growth of mango (Mangifera indica; Anacardiaceae) at the current-year branch scale

Premise of the study: Accurate and reliable predictive models are necessary to estimate nondestructively key variables for plant growth studies such as leaf area and leaf, stem, and total biomass. Predictive models are lacking at the current-year branch scale despite the importance of this scale in plant science. Methods: We calibrated allometric models to estimate leaf area and stem and branch (leaves + stem) mass of current-year branches, i.e., branches several months old studied at the end of the vegetative growth season, of four mango cultivars on the basis of their basal cross-sectional area. The effects of year, site, and cultivar were tested. Models were validated with independent data and prediction accuracy was evaluated with the appropriate statistics. Key results: Models revealed a positive allometry between dependent and independent variables, whose y -intercept but not the slope, was affected by the cultivar. The effects of year and site were negligible. For each branch characteristic, cultivar-specifi c models were more accurate than common models built with pooled data from the four cultivars. Prediction quality was satisfactory but with data dispersion around the models, particularly for large values. Conclusions: Leaf area and stem and branch mass of mango current-year branches could be satisfactorily estimated on the basis of branch basal cross-sectional area with cultivar-specifi c allometric models. The results suggested that, in addition to the heteroscedastic behavior of the variables studied, model accuracy was probably related to the functional plasticity of branches in relation to the light environment and/or to the number of growth units composing the branches. (Résumé d'auteur