Water use of individual Juniperus virginiana trees; How much, how variable, and what factors affect it

Background/Question/Methods

Woody plant encroachment into grasslands is an issue worldwide that has negative ecological and economic consequences. In the United States, J. virginiana is the primary invasive species in Oklahoma, Kansas and Nebraska. This shift from grassland to forest may result in changes in the water budget. Plant water use is a major component of the water budget, but measurements of J. virginiana water use are lacking. The objective of this study was to measure individual J. virginiana tree water uptake and determine how much it varies, and what factors affect it. Granier thermal dissipation probes were installed in trees of different diameters from low and high densities stands located in north central Oklahoma to measure daily water use. Relative humidity, wind velocity, soil moisture, and precipitation were also measured at the sites. 

Results/Conclusions

Preliminary results indicated that bigger trees used considerably more water than smaller trees. Due to larger crowns and higher light environments, trees in low density stands used more water than similarly sized trees from high density sites. Daily water used was highest in the months of May and June, which is consistent with warm temperature and high soil moisture availability, and decreased during drought. These preliminary results indicate that J. virginiana trees can use large quantities of water and the amount increases with tree size, soil moisture, and canopy openness. To finalize the water use estimates, we will calculate sapwood area and complete tree-specific calibrations.