Effects of eastern redcedar encroachment on soil hydraulic properties along Oklahoma's grassland‐forest ecotone

Abstract

AbstractIn north‐central Oklahoma eastern redcedar (Juniperus virginiana), encroachment into grassland is widespread and is suspected of reducing streamflow, but the effects of this encroachment on soil hydraulic properties are unknown. This knowledge gap creates uncertainty in understanding the hydrologic effects of eastern redcedar encroachment and obstructs fact‐based management of encroached systems. The objective of this study was to quantify the effects of eastern redcedar encroachment into tallgrass prairie on soil hydraulic properties. Leaf litter depth, soil organic matter, soil water repellency, soil water content, sorptivity, and unsaturated hydraulic conductivity were measured near Stillwater, OK, along 12 radial transects from eastern redcedar trunks to the center of the grassy intercanopy space. Eastern redcedar encroachment in the second half of the 20th century caused the accumulation of 3 cm of hydrophobic leaf litter near the trunks of eastern redcedar trees. This leaf litter was associated with increased soil organic matter in the upper 6 cm of soil under eastern redcedar trees (5.96% by mass) relative to the grass‐dominated intercanopy area (3.99% by mass). Water repellency was more prevalent under eastern redcedar than under grass, and sorptivity under eastern redcedar was 0.10 mm s−1/2, one seventh the sorptivity under adjacent prairie grasses (0.68 mm s−1/2). Median unsaturated hydraulic conductivity under grass was 2.52 cm h−1, four times greater than under eastern redcedar canopies (0.57 cm h−1). Lower sorptivity and unsaturated hydraulic conductivity would tend to decrease infiltration and increase runoff, but other factors such as rainfall interception by the eastern redcedar canopy and litter layer, and preferential flow induced by hydrophobicity must be examined before the effects of encroachment on streamflow can be predicted. Copyright © 2011 John Wiley & Sons, Ltd.