Woody plant encroachment alters soil hydrological properties and reduces downward flux of water in tallgrass prairie

Background and aims Plant and soil interact to shape ecosystem properties, processes and services provided. Changes in ecosystem productivity, biogeochemical cycling and plant herbivore interactions have been widely reported when herbaceous plants are replaced by woody plants, but limited information is available on how woody plant encroachment alters temporal dynamics of deep soil moisture and long-term drainage rates in the tallgrass prairie. Methods We quantified soil water content using capacitance probes for a period of four years, and used both chloride mass balance (CMB) and HYDRUS-1D modelling to depict alteration of deep soil water dynamics and long-term drainage rates after Juniperus virginiana (eastern redcedar) encroachment into the tallgrass prairie. Results Eastern redcedar encroachment resulted in more frequent depletion of soil water at the 80-cm depth. The chloride ion (Cl-) was used to estimate deep drainage rate because of its nonreactive nature. The ion is neither repelled nor absorbed by soil particles and sediments. Mean soil chloride concentration after encroachment was significantly higher than that in tallgrass prairie. The estimated deep drainage rate based on CMB method was 9.0 mm yr.(-1) in the tallgrass prairie and 0.3 mm yr.(-1) in the encroached site. The cumulative bottom fluxes were 27.5 cm and 17.1 cm in the tallgrass prairie and eastern redcedar encroached sites, respectively for the HYDRUS simulation period 2011-2014. Conclusions Transformation of tallgrass prairie to eastern redcedar woodland in the rolling hills of the southern Great Plains reduced soil water content, water storage and downward flux of water. Thus, woody plant encroachment into tallgrass prairie has the potential to reduce groundwater recharge in dry sub-humid regions.