| Over the last 150 years the ‘natural’ landscape in southeastern Ontario (as in much of the world) has undergone a dramatic transformation due, in large part, to widespread deforestation, wetland destruction and degradation, and increased agricultural activity. The negative impacts of such land-use modifications may include declines in wetland water quality and biodiversity. Here, I develop models to predict the effects of adjacent land-use on wetland water quality, and amphibian and plant diversity using indices of land-use intensity such as, forest cover, road density, building density, fertiliser application, livestock density etc. I find negative relationships between land-use intensity and wetland water quality, and amphibian and plant species richness. The strongest relationships tend to be with forest cover, however, other important variables include wetland size, road density, and the proportion of adjacent lands that is wetland. Moreover, there are complex interactions among variables. For instance, part of the effect of forest cover on plant and amphibian species richness may be indirect, through effects on wetland water quality but there are also effects of forest cover on both plants and amphibians that are independent of wetland water quality. In a conservation context, one important question is ‘what is the scale of adjacent land-use effects?’ I find that landscape modifications up to 2000–4000 meters from a wetland edge have the strongest correlations with wetland water quality and amphibian species richness while, land-uses 250–400 meters from the wetland edge are most strongly correlated with plant species richness. The conservation implication is that the current Ontario Wetland Policy which (1) evaluates and protects wetlands on a site-by-site basis and, (2) regulates adjacent land-use out to 120 meters from the wetland edge, is not likely to ensure long-term protection of wetland water quality and biodiversity in Ontario. |
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