Importance of riparian habitats to flora conservation in farming landscapes of southern Quebec, Canada

Plants of riparian habitats located between cropfields and linear watercourses, i.e., drainage ditches, streams, small rivers, situated in the Boyer river watershed were inventoried in Québec, eastern Canada. The main objectives of this study were to establish the contribution of narrow riparian habitat strips to plant biodiversity in farming landscape and to document whether they could be reservoir of weeds detrimental to agriculture. Twenty-nine sections (>400 m) of riparian habitats adjacent to cropfields were inventoried in summer 1996 and spring 1997, and these were grouped into five vegetation types: (1) herbaceous strips dominated by grasses and devoid of woody species, (2) herbaceous strips dominated by forbs also devoid of woody species, (3) strips with small (<2 m) shrubs, (4) strips with tall (between 2 and 10 m) shrubs, and (5) strips with mature trees (>10 m). A total of 280 (228 herbaceous and 52 woody) plant species were recorded. Overall habitats with trees contained a larger number of herb and woody species than other riparian habitats. However, this was not reflected in the species richness per unit area (quadrats) which meant that habitats with trees were more heterogeneous than other habitat types. Species composition differed considerably among the various riparian habitats when considering forest spring ephemerals, ferns, forbs in general, grasses and woody vegetation. Substantially more native wetland species (obligate and facultative) were recorded adjacent to watercourses than near fields. More weedy and in particular, introduced species, were found in quadrats sampled near cropfields. Although no plant species of special conservation value were located in the riparian habitats, they should deserve special protection in intensive agricultural areas because they harbour a suite of wetland plants (and animals) not found in other farmland habitats. This appears to be especially desirable for those habitats with a well-developed woody vegetation.