Ecosystem Engineering

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Vegetation patterning: Linking hydrologic and ecologic models


Figure (above) - False color (near infrared) imagery in which healthy vegetation appears red



      We present a modeling framework to understand and predict the hydrologic and ecologic differences between pristine, degraded, and restored meadow systems. Based on observed well hydrographs, the concept of a threshold vegetation hydrograph is introduced to distinguish between mesic and xeric vegetation communities using time-dependent, depth-to-water requirements. Three-dimensional, variably-saturated groundwater flow is simulated in an archetypical meadow system under conditions ranging from pristine to degraded to restored. Vegetation patterning is predicted by modeling the depth to the water table and applying the vegetation threshold hydrograph. Through an iterative process, we simulate feedback mechanisms between changing vegetation communities, evapotranspiration, and groundwater flow.
       This is apparently the first demonstrated approach in which the groundwater flow system in a riparian meadow system has been modeled and coupled to a vegetation model to predict vegetation patterning. It is a potentially useful approach for designing and improving the success of riparian restoration efforts in semi-arid environments and groundwater dependent ecosystems. The methodology also holds potential for helping to understand and predict feedback mechanisms between the hydrology, vegetation communities, and atmospheric water exchanges as driven by global climate change.


Figure:  Stream incision causes draining and aridification of soil zones near the channel resulting in swaths of xeric vegitation adjacent to the channel