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Environmental factors limiting success of revegetation on man-made waterfowl nesting islands in east-central Alberta

University of British Columbia

Vegetation and environment relationships were investigated on man-made earth islands in July and August of 1985 and 1986. The islands were built by Ducks Unlimited Canada to provide upland nesting cover for waterfowl. Twenty islands distributed throughout 12 wetlands (sloughs) were studied. The wetlands are located in east-central Alberta in the aspen parkland ecoregion. The flora and soils of each island were described. Correlation analysis was used to relate total and individual species foliar cover to environmental, primarily soil, variables. A point-intercept frame and a nestingboard were used to record foliar cover in 1-m² quadrats. Soils (0 - 15 cm depth) were collected within the quadrats. At least 3 quadrats/island were sampled. The quadrats were positioned on the islands using a stratified-random framework. The following soil properties were measured: total N (N) , pH, electrical conductivity, exchangeable and soluble cations, sodium adsorption ratio (SAR), exchangeable sodium percentage (ESP), cation exchange capacity (CEC), phosphorus (P) , organic carbon (C) , bulk density (BD), steady-state infiltration and porosity. The following site variables were measured: slope, aspect, microtopography, quadrat height-above-water, effervescence, and macrotopography (position on island). The island flora included 59 vascular species on 20 islands in 1985. In 1986, 40 species were recorded on 11 islands. Sow thistle (Sonchus ulignosus) and tall wheatgrass (Agropyron elongatum) were the most frequent species in 1985 and 1986, respectively. Yellow sweet clover (Melilotus officinalis) and tall wheatgrass had the greatest mean foliar cover in those years. Tall wheatgrass and yellow sweet clover were the most successful seeded species in terms of foliar cover and frequency; sow thistle, Canada thistle (Cirsium arvensis), and foxtail barley (Hordeum jubatum) were the most successful nonseeded species. Seeded species coverage averaged 20%, compared to 30% for nonseeded species. Island foliar cover was approximately 50% in 1985 and 1986, ranging from 14% at Kingston Slough to 89% at Louis Lake in 1985 and from 16% at Rollyview Marsh to 84% at Louis Lake in 1986. Island soils fit a continuum ranging from non-sodic and non-saline, with low bulk density fo sodic or saline-sodic, with high bulk density. Electrical- conductivity of the islands averaged 2.5 dS/m, bulk density averaged 1100 kg/m³, and pH ranged from 6.2 to 9.5. Total porosity and aeration porosity averaged .59.2% and 11.1%, respectively. SAR averaged 12.9. Foliar cover was not related to island age or the - time since seeding; nor was it related to the available weather variables. In general, island foliar cover was correlated with alkalinity, sodicity and bulk density. Seven variables were correlated with total foliar cover (point-intercept frame method) in 1985 and 1986: bulk density (-) , exchangeable Na (-) , pH (-) , organic carbon ( + ) , total N (+), and exchangeable Ca and Mg (+). Stepwise multiple correlation identified pH (-) , exchangeable Na (-), and bulk density (-) as having the best relationship with foliar cover in 1985 (r² = 0.64). The only difference in 1986 was the addition of electrical conductivity to the relationship (r² = 0.56). The relationships between nestingboard foliar cover and the environment were similar to those between total foliar cover and the environment. Alkalinity, sodicity and bulk density also exerted a strong influence on the coverage of individual species. Half of the dominant species were correlated (+ or -) with pH, and 30% were correlated with bulk density and exchangeable Na. Recommendations for establishing vegetation on man-made earth islands are provided.

Text

2010-08-16

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http://hdl.handle.net/2429/27423

Plant Science

University of British Columbia

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