A multivariate analysis examining the effect of landform on the distribution of riparian plant communities of Washington, USA

Mollot, L. A. and Bilby, R. E. and Chapin, D. M. (2008) A multivariate analysis examining the effect of landform on the distribution of riparian plant communities of Washington, USA. Community Ecology, 9 (1). pp. 59-72. ISSN 1585-8553

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Abstract

A considerable amount of research has been conducted on the influence of landform features on the distribution of vegetation on floodplains of major rivers. Considerably less work has examined this relationship along smaller channels in mountainous terrain. We utilized multivariate statistical techniques to examine the relationship between landform types and riparian plant floristics along small streams at the Cedar River Municipal Watershed in western Washington, USA. Riparian geomorphic surfaces were assigned to one of four landform classes based on topographic characteristics and position relative to the stream channel: low floodplain, high floodplain, terrace and hillslope. Landform exerted a strong influence on the distribution of tree, shrub and understory plant species. Certain taxa were found only on one or two of the landforms. Other species displayed a gradient in abundance across landforms. No single species occupied all landforms at the same level of abundance. The distribution patterns of species among the landforms suggested that primary drivers in the organization of the plant communities were moisture and susceptibility to disturbance. Plants preferring high moisture levels and resistant to the effects of fluvial disturbance typically were found on the floodplain landforms. Communities with hardwood-dominated overstories and dense shrub understories were prevalent on these sites. Slopes and terraces supported species able to cope with drier conditions and those unable to persist with frequent disturbance. Conifers were prevalent only on these drier, infrequently-disturbed landforms. These results indicate that restoration measures to increase the presence of conifer trees in riparian areas, a common activity in the Pacific Northwest, should be applied only on landforms that would naturally support these species.

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