Distribution, diversity, and traits of native, exotic, and invasive climbing plants in Michigan

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We compiled records of all the known climbing plant species both native and non-native in the state of Michigan, USA. County-level distributions and a broad suite of traits related to ecological and reproductive success were individually scored for each species. Non-native climbing species were subdivided and classified as either invasive or exotic. A total of 103 climbing species are present in the state, 50% of which are native. We classified only ten climbing species as currently invasive: of those 40% are woody, compared to 31% woody native and 33% woody exotic species. Our research asks whether latitude is correlated with either species richness or mode of dispersal among climbers. We also asked whether sexual system, dispersal mode, and unit of dispersal are different in native versus non-native climbers, and whether the dispersal mode of common trees is different from that of common climbers. We found latitudinally bimodal species richness for all classes of climbers, which we propose is due to collecting effort, growing season length, and human population density. We found surprisingly high numbers of climbing species at northern latitudes, in spite of harsh winter conditions, especially for climbing plants whose vascular tissues are compromised by freezing temperatures. Native species are significantly more often dioecious (27%) than non-natives (6%); however one of the woody invasive species, Celastrus orbiculatus, is functionally dioecious. Collectively, climbers include more abiotically dispersed species (62%) than biotically dispersed (38%). However, the 18 most common native species (found in more than 40 of 83 counties) are 61% biotically dispersed. Native woody climbers are 81% biotically dispersed, whereas native trees include 38–40% biotically dispersed species. Native climbing species are more often dispersed as fruits (52%) than are non-native climbers (37%), which are more often dispersed as seeds. Climbing mechanism is generally achieved by stem apical twining in both native and non-native species; however when tendrils are produced, native species produce similar proportions of leaf, petiole, and axillary tendrils, while non-native species largely produce leaf tendrils, a mechanism that is phylogenetically concentrated in the crop and crop-weed family, Fabaceae. Based on traits of the ten currently invasive climbing species in Michigan, we identify ten exotic species that are most likely to become invasive, most of which are perennials, hermaphroditic, with abiotically dispersed fruits, and modified climbing organs. Climbing species add significantly to biodiversity in Michigan, comprising 3.6% of the 2858 vascular plants. Climbing guilds in the temperate zone are more morphologically diverse and species rich than broadly recognized.