Plant diversity in natural woody, planted woody and herbaceous hedgerows adjacent to cropfields near Montreal, southern Quebec, Canada
Published source details
Boutin C., Jobin B., Bélanger L. & Choinière L. (2002) Plant diversity in three types of hedgerows adjacent to cropfields. Biodiversity and Conservation, 11, 1-25
Published source details Boutin C., Jobin B., Bélanger L. & Choinière L. (2002) Plant diversity in three types of hedgerows adjacent to cropfields. Biodiversity and Conservation, 11, 1-25
Hedgerows are linear structures comprising the woody and herbaceous flora (hedge-bottom flora) together with adjacent field margins (ecotones between the hedge and the field). In the intensive agricultural landscape of southern Quebec, Canada, as in similar areas devoted to agriculture elsewhere in North America, it is possible to observe three different types of hedgerows: 1) natural woody hedgerows, i.e., those remaining from larger forests or left to grow naturally between fields or more likely between adjoining farms, 2) planted woody hedgerows, i.e., those recently established by farmers for the reduction of wind erosion, also called windbreaks or shelterbelts, and 3) herbaceous hedgerows or fencerows which are devoid of trees but with a few scattered shrubs, and are by far the most common type of habitats abutting crop fields. In this study the value of the different types of hedgerows as repository of plant biodiversity in intensive farmland was compared.
Study area: In 1995, 61 hedgerows located in the lowland clay soil type of the St. Lawrence watershed in the Richelieu/Saint-Hyacinthe regions, southeast of Montreal in the Quebec province in eastern Canada (45º40'N, 72 º 40'W) were selected. The hedgerows were situated between intensively cropped fields, including maize, soybean, beans, peas, potatoes, other vegetable and small fruits.
Hedgerow surveys: From 5 to 19 July, woody and herbaceous plant species were surveyed in 730, 1 m² quadrats placed along the hedgerows: 27 natural (12 with trees; 15 with woody vegetation comprising shrubs only); 17 planted (six planted with trees; 11 planted with shrubs); and 17 herbaceaous.
In addition, biophysical characteristics were measured: width, length, distance from nearest woodlots, hedgerows, road and building.
The three types of hedgerows were quite different in their biophysical characteristics: tree and shrub layers, width, area, distance to woody habitats. The overall plant diversity was higher in natural hedgerows and they contained more plant species of conservation value than other hedgerow types. Plant species richness per quadrat was, however, higher in planted woody hedgerows, and together with the species composition, lead to the conclusion that planted hedgerows in their entirety consisted of an ecotone type of vegetation such as is found in field edges which usually support high plant diversity and productivity but where transient plant species predominate.
Conclusions: The preservation and sympathetic management of natural woody hedgerows emerges as pivotal for the conservation of many plants (and other wildlife) in intensively farmed areas otherwise deficient in woody habitats. Less than 30% of the area studied was covered with a very fragmented woodland cover, the fragmentation process being largely related to the intensity and types of agricultural practices. This holds for a number of intensively farmed areas in Canada and elsewhere. This study indicates that although natural hedgerows unequivocally fare better than planted or herbaceous hedgerows in terms of biodiversity of plants of conservation interest, planted woody hedgerows contained plant species of some interest and should be favoured over more desolate herbaceous hedgerows. Conceivably a diverse mixture of native deciduous and conifer trees should be encouraged in further windbreak planting programs. In addition, the management regime should optimise the establishment of plants that will accommodate both the conservation and agronomic objectives in areas where hedgerows were removed and are not re-establishing naturally.
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