Stand-Level Transpiration Increases after Eastern Redcedar (Juniperus virginiana L.) Encroachment into the Midstory of Oak Forests

Eastern redcedar (Juniperus virginiana L., redcedar) encroachment is transitioning the oak-dominated Cross-Timbers of the southern Great Plain of the USA into mixed-species forests. However, it remains unknown how the re-assemblage of tree species in a semiarid to sub-humid climate affects species-specific water use and competition, and ultimately the ecosystem-level water budget. We selected three sites representative of oak, redcedar, and oak and redcedar mixed stands with a similar total basal area (BA) in a Cross-Timbers forest near Stillwater, Oklahoma. Sap flow sensors were installed in a subset of trees in each stand representing the distribution of diameter at breast height (DBH). Sap flow of each selected tree was continuously monitored over a period of 20 months, encompassing two growing seasons between May 2017 and December 2018. Results showed that the mean sap flow density (Sd) of redcedar was usually higher than post oaks (Quercus stellata Wangenh.). A structural equation model showed a significant correlation between Sd and shallow soil moisture for redcedar but not for post oak. At the stand level, the annual water use of the mixed species stand was greater than the redcedar or oak stand of similar total BA. The transition of oak-dominated Cross-Timbers to redcedar and oak mixed forest will increase stand-level transpiration, potentially reducing the water available for runoff or recharge to groundwater.

Sustaining Cross-Timbers Forest Resources: Current Knowledge and Future Research Needs

The Cross-Timbers region of the United States, situated in the southern Great Plains along the western edge of the eastern deciduous forest, was historically Quercus-dominated open forest interspersed with tallgrass prairie and shrubs communities. The historical structure of the Cross- Timbers forests in this region has been altered, mainly due to fire exclusion, such that the current structure is closed-canopy and includes a midstory of fire-intolerant species. This change has reduced many of the important ecosystem services provided. This paper synthesizes existing literature on the Cross-Timbers with the aim of summarizing the current state of Cross-Timbers management related to sustaining ecosystem services and identifying potential research topics and directions needed. Specifically, we consider the ecological, management, and socio-economic issues. In addition, we theorize how the adoption of active forest management will affect ecosystem services and structure of the Cross-Timbers forests.

COUNTY RECORDS AND MAJOR RANGE EXTENSIONS FOR VASCULAR PLANTS FROM THE WEST CROSS TIMBERS IN ERATH COUNTY, TEXAS

Floristic data for Erath County, Texas, is unknown or limited. In this investigation plants were collected from 35 sites in Erath County from September 2003 to April 2008. Plants were identified and categorized based on the following status: introduced, endemic, threatened, and endangered species, as well as county records and major range extensions. One hundred and nineteen new county records were recorded for Erath County. Sixty five species were major range extensions, occurring greater than one county away from the border of Erath County. Twenty-six species were introduced while 93 species were native. Six of the native species were endemic to Texas, with Penstemon guadalupensis classified as endemic to north-central Texas and the Edwards Plateau. There were no rare, threatened, or endangered plants found. Convolvulus arvensis was the only noxious weed found, being state-listed as a noxious species.