Non-native Plant Invasions in Managed and Protected Ponderosa Pine/douglas-®r Forests of the Colorado Front Range

We examined patterns of non-native plant diversity in protected and managed ponderosa pine/Douglas-®r forests of the Colorado Front Range. Cheesman Lake, a protected landscape, and Turkey Creek, a managed landscape, appear to have had similar natural disturbance histories prior to European settlement and ®re protection during the last century. However, Turkey Creek has experienced logging, grazing, prescribed burning, and recreation since the late 1800s, while Cheesman Lake has not. Using the modi®ed-Whittaker plot design to sample understory species richness and cover, we collected data for 30 0.1 ha plots in each landscape. Topographic position greatly in¯uenced results, while management history did not. At both Cheesman Lake and Turkey Creek, low/riparian plots had highest native and non-native species richness and cover; upland plots (especially east/west-facing, south-facing and ¯at, high plots) had the lowest. However, there were no signi®cant differences between Cheesman Lake and Turkey Creek for native species richness, native species cover, non-native species richness, or non-native species cover for any topographic category. In general, non-native species richness and cover were highly positively correlated with native species richness and/or cover (among other variables). In total, 16 non-native species were recorded at Cheesman Lake and Turkey Creek; none of the 16 non-native species were more common at one site than another. These ®ndings suggest that: (1) areas that are high in native species diversity also contain more non-native species; (2) both protected and managed areas can be invaded by non-native plant species, and at similar intensities; and (3) logging, grazing, and other similar disturbances may have less of an impact on non-native species establishment and growth than topographic position (i.e., in lowland and riparian zones versus upland zones). Published by Elsevier Science B.V.