Shrub effects on seeding establishment, 2019 - 2020.

Plant communities in mountain ecosystems are particularly vulnerable due to amplified rates of warming (Pepin and Lundquist, 2008; Pepin et al., 2015) and declines in snowpack (Fyfe et al., 2017). As a result of these global change drivers, there is a widespread pattern of biotic shifts in the alpine (Bueno de Mesquita et al., 2018). However, it is unclear how important these biotic shifts will be in mediating the response of other species to global change. For example, the uphill movement and expansion of structure-forming species (e.g. trees, shrubs, cushion plants), can create small-scale variations in the conditions experienced by species (microclimates) through their effects on snow, wind, solar radiation, and soil properties (Holtmeier and Broll, 1992; Seastedt and Adams, 2001; Pistón et al., 2018; Chen et al., 2019). One such expanding structure-forming group of species are shrubs—the expansion and densification of shrubs is occurring in arctic and alpine zones across the globe (Myers-Smith et al., 2011; Formica et al., 2014; Elmendorf et al., 2012b, 2012a).Shrub microclimatic effects can alter fine-scale variability across the landscape, which may have important consequences for plant communities through increased heterogeneity and modified exposure. For instance, the microclimatic effects shrubs in the alpine may facilitate the establishment of subalpine species that need to migrate uphill to track their climatic niche (Akhalkatsi et al., 2006; Martínez, 2012; Cranston and Hermanutz, 2013). References Akhalkatsi, M., Abdaladze, O., Nakhutsrishvili, G., and Smith, W. K., 2006: Facilitation of seedling microsites by Rhododendron caucasicum extends the Betula litwinowii alpine treeline, Caucasus Mountains, Republic of Georgia. Arctic, Antarctic, and Alpine Research, 38(4):481–488. Bueno de Mesquita, C. P., Tillmann, L. S., Bernard, C. D., Rosemond, K. C., Molotch, N. P., and Suding, K. N., 2018: Topographic heterogeneity explains patterns of vegetation response to climate change (1972–2008) across a mountain landscape, Niwot Ridge, Colorado. Arctic, Antarctic, and Alpine Research, 50(1). Chen, J. G., He, X. F., Wang, S. W., Yang, Y., and Sun, H., 2019: Cushion and shrub ecosystem engineers contribute differently to diversity and functions in alpine ecosystems. Journal of Vegetation Science, 30(2):362–374. Cranston, B. H., and Hermanutz, L., 2013: Seed-seedling conflict in conifers as a result of plant-plant interactions at the forest-tundra ecotone. Plant Ecology and Diversity, 6(3–4):319–327. Elmendorf, S. C., Henry, G. H. R., Hollister, R. D., Björk, R. G., Bjorkman, A. D., Callaghan, T. V., Collier, L. S., Cooper, E. J., Cornelissen, J. H. C., Day, T. A., Fosaa, A. M., Gould, W. A., Grétarsdóttir, J., Harte, J., Hermanutz, L., Hik, D. 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A., Michelsen, A., Molau, U., Myers-Smith, I. H., Oberbauer, S. F., Onipchenko, V. G., Rixen, C., Martin Schmidt, N., Shaver, G. R., Spasojevic, M. J., Pórhallsdóttir, P. E., Tolvanen, A., Troxler, T., Tweedie, C. E., Villareal, S., Wahren, C. H., Walker, X., Webber, P. J., Welker, J. M., and Wipf, S., 2012b:. Plot-scale evidence of tundra vegetation change and links to recent summer warming. Nature Climate Change, 2(6):453–457. Formica, A., Farrer, E. C., Ashton, I. W., and Suding, K. N., 2014: Shrub expansion over the past 62 years in Rocky Mountain alpine tundra: possible causes and consequences. Arctic, Antarctic, and Alpine Research, 46(3):616–631. Fyfe, J. C., Derksen, C., Mudryk, L., Flato, G. M., Santer, B. D., Swart, N. C., Molotch, N. P., Zhang, X., Wan, H., Arora, V. K., Scinocca, J., and Jiao, Y., 2017: Large near-Term projected snowpack loss over the western United States. Nature Communications, 8:1–7. Holtmeier, F. K., and Broll, G., 1992: The influence of tree islands and microtopography on pedoecological conditions in the forest-alpine tundra ecotone on Niwot Ridge, Colorado Front Range, USA. Arctic & Alpine Research, 24(3):216–228. Martínez, M. L., 2012: Facilitation of seedling establishment by an endemic shrub in tropical coastal sand dunes. Plant Ecology, 168(2):333–345. Myers-Smith, I. H., Forbes, B. C., Wilmking, M., Hallinger, M., Lantz, T., Blok, D., Tape, K. D., MacIas-Fauria, M., Sass-Klaassen, U., Lévesque, E., Boudreau, S., Ropars, P., Hermanutz, L., Trant, A., Collier, L. S., Weijers, S., Rozema, J., Rayback, S. A., Schmidt, N. M., Schaepman-Strub, G., Wipf, S., Rixen, C., Ménard, C. B., Venn, S., Goetz, S., Andreu-Hayles, L., Elmendorf, S., Ravolainen, V., Welker, J., Grogan, P., Epstein, H. E., and Hik, D. S., 2011: Shrub expansion in tundra ecosystems: dynamics, impacts and research priorities. Environmental Research Letters, 6(4). Myers-Smith, I. H., and Hik, D. S., 2013: Shrub canopies influence soil temperatures but not nutrient dynamics: an experimental test of tundra snow-shrub interactions. Ecology and Evolution, 3(11):3683–3700. Pepin, N., Bradley, R. S., Diaz, H. F., Baraer, M., Caceres, E. B., Forsythe, N., Fowler, H., Greenwood, G., Hashmi, M. Z., Liu, X. D., Miller, J. R., Ning, L., Ohmura, A., Palazzi, E., Rangwala, I., Schöner, W., Severskiy, I., Shahgedanova, M., Wang, M. B., Williamson, S. N., and Yang, D. Q., 2015: Elevation-dependent warming in mountain regions of the world. Nature Climate Change, 5(5):424–430. Pepin, N. C., and Lundquist, J. D., 2008: Temperature trends at high elevations: patterns across the globe. Geophysical Research Letters, 35(14):1–6. Pistón, N., Michalet, R., Schöb, C., Macek, P., Armas, C., and Pugnaire, F. I., 2018: The balance of canopy and soil effects determines intraspecific differences in foundation species’ effects on associated plants. Functional Ecology, 32(9):2253–2263. Seastedt, T. 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