Plant communities of selected urbanized areas of Halifax, Nova Scotia, Canada

This study was designed to compare plant biodiversity and community indicators among urban residential areas and more-natural habitats in the vicinity of Halifax, Nova Scotia. Six house lots were examined in each of three age-categories of residential neighborhoods (>80 years, 30-50 years, and <10 years), and these were compared to four forested plots in semi-natural urban parks and four in a natural forest. The residential areas represented broad stages of successional development of “urban forest,” while the stands of semi-natural and natural forest are representative of the original habitats that have been converted into residential land-use. In general, the observed plant species richness was much higher in the residential areas, but these habitats were strongly dominated by non-indigenous species whereas the natural and semi-natural habitats supported native taxa. This obvious difference between residential areas and semi-natural/natural habitats was confirmed by cluster analysis and principal components analysis, both of which separated the sample sites into two groups of plant communities. Neighborhood age and proximity of the residential sites had little influence on these multivariate analyses, suggesting that site-specific management practices (such as horticultural choices of landowners) had a strong influence on plant-community structure. Woody vegetation (trees and shrubs) in the semi-natural and natural forest had a higher basal area and stored more biomass and carbon than in residential habitats. However, there was a successional progression in the urban forest, in that older habitats stored much more woody carbon than younger ones. Although well-vegetated residential neighborhoods provide important environmental services, their striking dominance by exotic species, as well as their lower carbon storage in vegetation, contribute to an impoverishment of ecological integrity. This circumstance could be partially mitigated by changing horticultural management to encourage naturalization, particularly through the planting of indigenous species.