Abstract

Eastern redcedar (Juniperus virginiana L.) is rapidly encroaching and degrading native prairie and rangeland landscapes in the Great Plains of the U.S. Little is known concerning the impacts of increasing redcedar density and areal coverage on local and regional water budgets through transpiration (T_r) and canopy interception (C_I) of precipitation. Limited T_r and C_I studies have been conducted in dense stands of redcedar but results from these studies may not be applicable to redcedar growing in open environments. Four redcedar trees (two large, two small) were located in central Oklahoma to measure T_r. Two limbs (one on the north face and one on the south face) on each of the large trees were instrumented with sapflux sensors to measure T_r from August 2010 through mid-July 2012. Limb level T_r was scaled to tree level T_r using ratios of both leaf and bole areas. Whole tree T_r was measured on two small redcedar trees from mid-May 2011 through mid-July 2012. Transpiration of the small redcedars was found to respond quickly to precipitation events, while the large redcedars did not. Redcedar T_r was compared to that of native grasses. The large redcedars exhibited higher T_r rates than native grasses while the small redcedars transpired at rates closely matching native grasses. Four different redcedars were instrumented to measure C_I from October 2009 through mid-July of 2012. Redcedar canopies were found to intercept 100% of precipitation for events ? 2.4 mm. Redcedar canopies reduce annual precipitation received at the surface by about 33%, and as much as 39% in the western portion of the state. Significant canopy interception of precipitation, coupled with T_r rates as large as or larger than native grasses and with year-round T_r, suggests increases in redcedar density and areal coverage could affect local water resources (e.g. reducing infiltration, runoff, and ground water recharge rates).

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