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UBC Theses and Dissertations

Plant species abundance, diversity and soil quality of grassland set-asides on the Fraser River delta Principe, Laura Lee


This project included the monitoring and evaluation of a sample of set-asides enrolled in the Delta Farmland and Wildlife Trust's Grassland Set-aside Program. The Setaside program is one of several farmland stewardship programs in the Fraser River Delta of British Columbia and its objectives include soil conservation and wildlife habitat creation. Vegetative characteristics and soil quality were studied at both small plot and multifield levels on sites enrolled in the Delta Farmland and Wildlife Trust's Grassland Set-aside Program. At the small plot site, the effects of a manure application and two nurse crops (barley and annual ryegrass) on plant canopy characteristics and soil quality of a grassland set-aside seed mix were compared to a control (no manure or nurse crop). Indices for measuring vegetative characteristics included plant species abundance (Braun-Blanquet Cover-abundance Scale, species frequency and biomass), species richness (number of species found on a site) and species diversity (average number of species per quadrat). For the small plot site, the main soil quality indicators included mean weight diameter (MWD) and water stable aggregates (WSA), while at the multi-field level soil pH, electrical conductivity (EC) and sodium adsorption ratio (SAR) were more relevant. At the small plot study, between May and August of 1998, weeds were most effectively suppressed by barley>annual ryegrass>no nurse. Similarly, the biomass of the seeded species was suppressed in the order barley>annual ryegrass>no nurse. No significant effect of the nurse crop was found on the abundance of seeded species beyond the fall of 1998. There was no significant effect of either nurse crop treatment or establishment of the grass stand on MWD or WSA. The manure application significantly increased the total and the seeded species biomass (p=0.1). Cover by orchard grass (Dactylis glomerata) was significantly higher and cover by short fescues (Festuca rubra spp.) was significantly lower with manure application. A correlation analysis between biomass and percent cover across all nurse crop and fertility treatments over two years showed that cover and biomass were significantly and positively correlated. At the multi-field level, a regression analysis between percent cover and pH and EC was significant for timothy, short fescue and the seeded species as a group (p<0.1). EC was found to have a greater effect than pH in four of five analyses. As a set-aside matured, species richness remained relatively stable, biomass peaked then stabilized, species diversity decreased and plant-litter accumulated. Variation among sites was high due to uncontrollable factors such as time and method of seeding, weather conditions during germination, fertilizer regimes, soil quality and site history. Results from this study indicate that... 1. The farmer's choice of nurse crop does affect total cover and biomass in the first summer of a set-aside, but is unlikely to affect soil quality or vegetation characteristics of the set-aside after the establishment year. 2. Measures of cover using a Braun-Blanquet cover-abundance scale give similar results as biomass measures. 3. Soil factors most likely to limit successful establishment of the set-aside mix rank as follows; salinity>water problems>low pH. 4. A grassland set-aside is not able to remediate severely degraded soils where an existing soil drainage problem is not corrected before establishment.

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