Soil Water Content Dynamics Along a Range Condition Gradient in a Shortgrass Steppe

Evidence is accumulating on the importance of plant cover and plant species composition on the control of ecosystem processes. In this study we examined a gradient considering the proportional contribution of the key species Bouteloua gracilis H.B.K. Lag. to assess its influence on the average and dynamic changes in soil water content in the shortgrass steppe from Central Mexico. We chose 4 sites with the following proportions of the key species: < 25%, 25%–50%, 50%–75%, and > 75%, ascribing each proportion to the range condition categories poor, fair, good, and excellent, respectively. Soil water measurements were carried out during 14 months at the 4 sites. Our results showed that range condition had a significant effect on soil water content (P < 0.01). The excellent condition was overall 14.5% and 12.5% lower soil moisture content compared to the poor and good range conditions (P < 0.01), respectively. Our results indicated a negative correlation between the gradient of soil water content with the range condition classes. Soil water content dynamics also differed among range condition classes, with the excellent condition showing both faster water recharge and extraction patterns than the other 3 range condition categories. Differences in soil water content among the range condition classes appeared to be related to morphological and physiological traits associated with the dominant species cover observed at each site. These results offer insights into the importance of vegetation characteristics as potential indicators of thresholds in grazing ecosystem processes such as soil water dynamics.