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

Abstract

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.

The role of species interactions for forest resilience to drought

“…2019; Torquato et al . 2020). However, there is evidence that under increasing drought stress, species interactions can shift from a positive to a negative interaction because of increasing niche overlap (Rodríguez‐Robles et al .…”

Improved productivity, water yield, and water use efficiency by incorporating switchgrass cultivation and native ecosystems in an integrated biofuel feedstock system

“…Norris et al (2001) found that eastern redcedar stands in the Great Plains ranged from 7 Mg ha −1 year −1 in a 70 year old stand to over 10 Mg ha −1 year −1 for a 35 year old stand from an area with precipitation (average 835 mm per year) similar to our site. Based on aerial imagery and coring of several trees (Nunes Biral et al, 2019; Torquato, Will, et al, 2020), the eastern redcedar in our study were approximately 40 years old. The standing biomass of our eastern redcedar stands (61 and 112 Mg ha −1 ) also was lower than estimates from Norris et al (2001) where standing biomass ranged from 114 to 211 Mg ha −1 .…”

“…Post oak is a slow growing species and its growth is sensitive to low precipitation (Stahle & Hehr, 1984). A subset of post oaks measured at our site averaged 95 years old (Torquato, Will, et al, 2020). Another factor that impacted the productivity of the oak watersheds was the encroachment of eastern redcedar into the forest.…”

Ecohydrological connectivity: A unifying framework for understanding how woody plant encroachment alters the water cycle in drylands

“…In addition, runoff dynamics were altered: whereas runoff from grasslands was typically generated as saturation overland flow, that from the juniper-encroached sites was generated as infiltration-excess overland flow (Qiao et al, 2017). These ecohydrological changes are being driven largely by higher transpiration and interception losses in the juniper woodlands (Caterina et al, 2014;Wang et al, 2018b;Torquato et al, 2020). Modeling exercises and historical streamflow records suggest that these smaller-scale changes will result in reduced streamflows at larger scales (Zou et al, 2016;Starks and Moriasi, 2017).…”