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      The role of vegetation-microclimate feedback in promoting shrub encroachment in the northern Chihuahuan desert.

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          Abstract

          Many arid and semi-arid landscapes around the world are affected by a shift from grassland to shrubland vegetation, presumably induced by climate warming, increasing atmospheric CO2 concentrations, and/or changing land use. This major change in vegetation cover is likely sustained by positive feedbacks with the physical environment. Recent research has focused on a feedback with microclimate, whereby cold intolerant shrubs increase the minimum nocturnal temperatures in their surroundings. Despite the rich literature on the impact of land cover change on local climate conditions, changes in microclimate resulting from shrub expansion into desert grasslands have remained poorly investigated. It is unclear to what extent such a feedback can affect the maximum extent of shrub expansion and the configuration of a stable encroachment front. Here, we focus on the case of the northern Chihuahuan desert, where creosotebush (Larrea tridentata) has been replacing grasslands over the past 100-150 years. We use a process-based coupled atmosphere-vegetation model to investigate the role of this feedback in sustaining shrub encroachment in the region. Simulations indicate that the feedback allows juvenile shrubs to establish in the grassland during average years and, once established, reduce their vulnerability to freeze-induced mortality by creating a warmer microclimate. Such a feedback is crucial in extreme cold winters as it may reduce shrub mortality. We identify the existence of a critical zone in the surroundings of the encroachment front, in which vegetation dynamics are bistable: in this zone, vegetation can be stable both as grassland and as shrubland. The existence of these alternative stable states explains why in most cases the shift from grass to shrub cover is found to be abrupt and often difficult to revert.

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          Author and article information

          Journal
          Glob Chang Biol
          Global change biology
          Wiley-Blackwell
          1365-2486
          1354-1013
          Jun 2015
          : 21
          : 6
          Affiliations
          [1 ] Department of Environmental Sciences, University of Virginia, 291 McCormick Rd, Charlottesville, VA, 22904-4123, USA.
          Article
          10.1111/gcb.12856
          25581578
          d6cfa8fd-1d53-42d9-a156-86c0964f3200
          History

          shrub encroachment,vegetation-microclimate feedback,weather research and forecasting model,Larrea tridentata,cold stress,mesoscale modeling,minimum temperature

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