The distribution and habitat associations of non-native plant species in urban riparian habitats

• Published in: Journal of vegetation science Vol. 17; no. 4; pp. 499 - 508
• Main Authors: Maskell, L. C, Bullock, J. M, Smart, S. M, Thompson, K, Hulme, P. E
• Format: Journal Article
• Language: English
• Published: Blackwell Publishing Ltd 01.08.2006; Opulus Press
• Subjects: Alien; annuals; Biological invasion; Ecological invasion; eutrophication; Fallopia; floodplains; forbs; grasslands; Habitat preference; habitats; Impatiens; indigenous species; Introduced species; invasive species; land use; leaf area; light intensity; Native species; perennials; Plant attribute; plant communities; Plants; riparian areas; Riparian ecology; Riverine habitats; rivers; shrublands; Species diversity; Species richness; Urban ecology; Urban habitats; vascular plants; Vegetation
• ISSN: 1100-9233; 1654-1103; 1104-7402
• DOI: 10.1658/1100-9233(2006)17[499:TDAHAO]2.0.CO;2

Questions: 1. What are the distribution and habitat associations of non-native (neophyte) species in riparian zones? 2. Are there significant differences, in terms of plant species diversity, composition, habitat condition and species attributes, between plant communities where non-natives are present or abundant and those where non-natives are absent or infrequent? 3. Are the observed differences generic to non-natives or do individual non-native species differ in their vegetation associations? Location: West Midlands Conurbation (WMC), UK. Methods: 56 sites were located randomly on four rivers across the WMC. Ten 2 m × 2 m quadrats were placed within 15 m of the river to sample vegetation within the floodplain at each site. All vascular plants were recorded along with site information such as surrounding land use and habitat types. Results: Non-native species were found in many vegetation types and on all rivers in the WMC. There were higher numbers of non-natives on more degraded, human-modified rivers. More non-native species were found in woodland, scrub and tall herb habitats than in grasslands. We distinguish two types of communities with non-natives. In communities colonized following disturbance, in comparison to quadrats containing no non-native species, those with non-natives had higher species diversity and more forbs, annuals and short-lived monocarpic perennials. Native species in quadrats containing non-natives were characteristic of conditions of higher fertility and pH, had a larger specific leaf area and were less stress tolerant or competitive. In later successional communities dominated by particular non-natives, native diversity declined with increasing cover of non-natives. Associated native species were characteristic of low light conditions. Conclusions: Communities containing non-natives can be associated with particular types of native species. Extrinsic factors (disturbance, eutrophication) affected both native and non-native species. In disturbed riparian habitats the key determinant of diversity is dominance by competitive invasive species regardless of their native or non-native origin. Nomenclature: Stace (1991).