Native and invasive vegetation of karst springs in Wisconsin’s Driftless area

Abstract

Little is known about the vegetation found in the karst springs of Wisconsin’s unglaciated region, the Driftless Area. We sampled 26 of these springs, documenting all associated plant species and their status (native, non-native, invasive) and analyzed whether vegetation patterns are related to spring orientation or to spring area. Two-way ANOVA results show that non-native and invasive species, namely Nasturtium officinale (watercress, Brassicaceae), are significantly more abundant than natives in north-facing springs (p < 0.01), but not in south-facing springs. Generally, native species are restricted to, or more abundant in, south-facing springs, and may have a microtopographical preference for these sites, which may receive more direct solar radiation. Nasturtium officinale, the most abundant invasive species, has high cover values in both north and south orientations and is less restricted in its distribution. Correlation analysis shows that the larger the spring, the higher the percent of Nasturtium (p < 0.01) and invasive species cover (as a percent of spring area) (p < 0.005). Larger springs often had slower moving water and this may have contributed to the success of Nasturtium, which may outcompete shade-intolerant natives in the larger springs. Native species cover was negatively related to spring area, though this result was marginally insignificant (p = 0.08).