DISTRIBUTION AND ASSOCIATED ARTHROPODS OF NATIVE AND NON-NATIVE THISTLES IN THE VALLES CALDERA NATIONAL PRESERVE, NEW MEXICO, USA
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Non-native plant species represent an important threat to rangeland health and productivity. In New Mexico highland range, four non-native species of interest, Cirsium vulgare, C. arvense, Carduus nutans, and Bromus tectorum, are irregularly and patchily distributed across a diverse and disturbed landscape. In this study I surveyed the Valles Caldera National Preserve (VCNP) for target non-native species and mapped their distribution and abundance. I measured trends in non-native species abundance and distribution using road surveys, chance encounters, and targeted search efforts. I then correlated non-native species distribution to fire treatment, burn severity, aspect, and logging history with none being significant. Non-native plant species occurred more frequently at burned sites then at unburned sites, with high severity sites having the highest occurrence of invasive plants. Furthermore, areas of dense forest that are being thinned to mitigate fire danger may exhibit the same non- native species response as areas impacted by high severity burns. Arthropod community interactions with native and non-native thistle species are also an important component of rangeland health and productivity. Arthropod taxonomic richness and abundance were compared between one non- native species of thistle, Cirsium vulgare, and one native species of thistle, C. pallidum. I collected 22 C. vulgare thistle plants and 24 C. pallidum thistle plants and then sampled and identified the insect families and functional groups present on those plants. I found that spiders and moths/butterflies showed differences between thistle species. Beetles were more abundant on the native i thistle. We also grouped taxa by functional feeding group using readily available life history information. Taxonomic richness differed between thistle species, with native thistles having significantly more taxa. Predators and pollinators were more abundant on native thistles. These results will inform land management decisions regarding non- native species occurrence in areas of high disturbance like those impacted by restoration efforts and or wildland fire. While it is difficult to predict the occurrence and/or frequency of disturbance in many cases, understanding post- disturbance trends is vital when managing land for productivity long term. As wildland fire continues to increase in frequency and intensity in the southwestern United States, management issues such as the ones being addressed on VCNP (e.g., biodiversity preservation and biological invasions) will become more commonplace and widespread. Thistle invasion has the potential to comprise long-term rangeland health and productivity, and insect communities that occur on these thistles may represent case studies for more wide-scale responses to plant invasions. In addition, local insect communities provide a cascade of benefits to their ecosystem (e.g., pollination, prey, decomposition, predation, parasitism, etc..) and invasion-driven changes in abundance and diversity may compromise ecosystem health.