Comparison of the vegetation and seedbanks of soybean fields, adjacent boundaries, and hedgerows in Ontario

Abstract

Boutin, C. 2006. Comparison of the vegetation and seedbanks of soybean fields, adjacent boundaries, and hedgerows in Ontario. Can. J. Plant Sci. 86: 557-567. Patterns of plant assemblages in habitats located within agroecosystems are poorly understood. A study of the seedbank and standing vegetation in 10 soybean [Glycine max (L.) Merr.] fields, their adjacent boundaries, and adjoining woody hedgerows was undertaken in Ontario. The objective was to examine the composition of plants of conservation value and weedy species in these habitats. The seedbank of each habitat was determined from soil cores in quadrats located at regular intervals along transects, using the seedling emergence method in the greenhouse. The vegetation was surveyed in plots adjacent to the seedbank sampling areas. There was no significant difference in total species richness of vegetation or the seedbank among habitat types. However, there was a marked difference in species composition. In the seedbank, no difference in weed species richness among habitats was observed. In vegetation, however, fields harboured significantly more weedy species than adjacent boundaries and hedgerows. The dissimilarity between the seedbank and the vegetation was confirmed in detrended correspondence analyses, which showed that hedgerow vegetation, and to a lesser extent boundary vegetation, differed from field vegetation and all the habitats of the seedbank. The analysis of soil properties indicated that organic matter and nutrient levels were often higher in hedgerows than in fields. It can be concluded that hedgerows are valuable habitats for plant diversity and that weed species represent a minor component of their overall vegetation composition. On a identifié les semences présentes dans chaque habitat à partir des carottes de sol prélevées dans des cadrats situés à intervalles réguliers le long de transects, en recourant à la méthode de germination en serre. Les plantes dans les parcelles contiguës aux sites échantillonnés pour l'identification des semences ont égale-ment été recensées. La diversité globale des espèces identifiées d'après leur graine ne varie pas de manière significative avec l'habitat. Cependant, on note une nette variation dans la composition des espèces. Ainsi, pour les semences, la diversité des adventices ne varie pas avec l'habitat. En revanche, dans la végétation, on constate que les champs abritent considérablement plus d'espèces adventices que les bordures et les haies adjacentes. Cette différence entre les semences et la végétation est confirmée par l'analyse des correspondances après suppression des tendances. Celle-ci révèle que la végétation dans les haies et, dans une moindre mesure, celle des terrains limitrophes, diffèrent de celle qu'on trouve dans les champs ainsi que les habitats d'où viennent les semences. L'analyse des propriétés du sol indique que la concentration de matière organique et d'éléments nutritifs est souvent plus élevée dans les haies que dans les champs. On en conclut que les haies constituent un habita...

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