Woody vegetation removal effects on soil moisture depend strongly on soil texture

Background/Question/Methods

Shifts in vegetation composition have the potential to affect a variety of ecosystem processes.  In the grasslands of south Texas, increases in woody vegetation are known to have altered carbon and nutrient cycling rates and pool sizes in soils, often increasing both.  Due in part to increasing human demand for water, there has been a growing interest in how woody encroachment may alter the hydrologic cycle.  To better understand the effects of woody vegetation removal, a large manipulative experiment was established to investigate the role of woody vegetation on soil water dynamics.  Woody vegetation was removed using roller chopping and cut-stump on sandy, loam and clay loam soils in a full-factorial, replicated study.  Soil profile water was measured with a neutron probe to 2 m and compared for 13 months following treatments.  Precipitation during the study was well below normal (~70%) and so our results reflect responses in a very low input period. Soil water content was split into 3 depth increments (0-60 cm, 60-120 cm, and 120-180 cm) and soil x vegetation removal treatments were compared over time.  

Results/Conclusions

Changes in soil water content were significant for three months in shallow soils (0-60 cm), with the greatest treatment response in loam and clay loam soils.  Seven months had significant changes in the mid soils (60-120 cm), where sandy or sandy roller chop soils had the greatest treatment response.  One month had a significant change in deep soils (120-180 cm), with the greatest change in sandy roller chopped soils. Surprisingly, roller chopping reduced total soil profile water in clay loam soils throughout the sampling period.  Loam was similar to clay loam soils in response to vegetation removal treatments.  There was no effect of vegetation removal on total soil water profiles in sandy soils.  During the time period of observation, vegetation removal had minimal effect on deep soil water in the mesquite shrubland of south Texas.

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