At the same time, plants strongly regulate the distribution of water in the soil. Given this coupling, it is expected that soil moisture-plant interactions play an important role in the invasion of semiarid grasslands by shrubs. These changes decrease the water available for use by grasses such as Black Gramma, except beneath shrub canopies. If this hypothesis is accurate, then a positive feedback between shrub invasion and soil moisture changes should exist. We will accomplish this objective by assessing differences in soil water content and matric potential across the grass-shrub ecotone, including spatial distribution and temporal variability.
Water content is important for assessing changes in the water balance.
Matric potential is important in terms of modifications of plant-water relations and infiltration. Various elements of the water balance in grass and shrub environments have previously been measured, at the Sevilleta and elsewhere. Two key differences exist between our planned monitoring and previous efforts. We have measured the soil moisture content and wetting front following several rainfall events, in both grass and shrub environments. Samples were located at 10 cm intervals along two 24 m perpendicular transects.