ARS | Publication request: Effects of thinning on transpiration by riparian buffer trees in response to advection and solar radiation

Submitted to: Acta Horticulturae
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: March 15, 2012
Publication Date: August 18, 2012
Citation: Hernandez-Santana, V., Asbjornsen, H., Sauer, T.J., Isenhart, T., Schilling, K., Schultz, R. 2012. Effects of thinning on transpiration by riparian buffer trees in response to advection and solar radiation. Acta Horticulturae. 951:225-231. Available: http://www.actahort.org/books/951/951_27.htm.

Interpretive Summary: Trees are planted along streams as a conservation practice to improve water quality, reduce erosion, and increase perennial plant cover. There is some concern that these trees could take up too much water and reduce stream flow or take water from crops. In this study sensors were placed in trees along Bear Creek in central Iowa to measure their water use. After some measurements were taken, some of the trees next to the ones with sensors were cut down to see if evaporation would increase if more light got to the remaining trees. Other sensors measured wind speed and air temperature and humidity in the field upwind and in three locations in and near the tree rows. The results indicated that trees along the upwind edge used more water (around 40% more on average). This was likely due to being exposed to warm, dry air flowing over the crops. Thinning did increase individual tree water use but total water used was not affected much due to the reduced number of trees. These results are of interest to scientists, resource managers, and policy makers interested in managing water use in agricultural regions and in estimating additional water use by trees exposed to warm, dry winds.

Technical Abstract: Advective energy occurring in edge environments may increase tree water use. In humid agricultural landscapes, advection-enhanced transpiration in riparian buffers may provide hydrologic regulation; however, research in humid environments is lacking. The objectives of this study were to determine how water use by trees growing in a riparian buffer in central Iowa is influenced by 1) advective energy, 2) tree position, and 3) thinning (40% LAI reduction). We measured meteorological variables and sap flux density from July to September in 13 trees (2009) and 12 trees (2010) in one thinned plot (TP, treated in Aug 2010) and one untreated (control) plot (UP). The difference in Qs between edge and interior trees (39% higher in 2009) was attributed to the advective energy at the buffer edge. After thinning, maximum Qs increased was greater in TP compared to UP, explained primarily by solar radiation (R2=0.7, p<0.05), since meteorological conditions were not optimal for advection. However, the LAI reduction counteracted the increase in whole tree Qs, such that post-treatment plot transpiration per LAI measured from TP (0.4 mm day-1) was less than for UP (0.5 mm day-1).