Use of thermal dissipation probes to estimate water loss of containerized landscape trees.
Granier style thermal dissipation probes (TDPs) have been used to estimate whole plant water use on a variety of tree and vine species. However, studies using TDPs and load cells (gravimetric water loss) to estimate water use of landscape tree species are rare. This research compared gravimetric water loss (estimated with load cells) of four containerized landscape tree species with water loss estimated with TDPs. Over a 66 day period, an experiment compared water loss of three established, 5.0 cm (2 in) caliper poplar (Populus nigra ‘Italica’) trees in 75-liter (20 gal) containers on load cells to TDP estimated water loss. Each tree had a single 30 mm (1.2 inch) TDP inserted into the trunk at four heights above soil level (15, 30, 45, and 60 cm (6, 12, 18, and 24 in, respectively)). Data revealed TDP estimated water loss was less than load cell estimated water loss regardless of TDP height, but TDP estimated water loss at the 30 cm height was closest to actual load cell estimated tree water loss. Over the next three years, similar sized Bradford pear (Pyrus calleryana ‘Bradford’), English oak (Quercus robur x Q. bicolor‘Asjes’), poplar (Populus deltoides ‘Siouxland’), and sweetgum (Liquidambar styraciflua ‘Rotundiloba’) trees in containers were placed on load cells and one 30 mm TDP was placed into the trunk of each tree 30 cm above soil level. Over an extended time period, tree water loss was estimated using load cells and TDPs. Hourly TDP water loss estimates for each species over a three day period indicate TDP estimated water loss followed similar trends as load cell estimated water loss. However, TDP estimates were generally less than load cell estimates, especially during peak transpiration periods. For each species, mean total daily water loss estimates were less for TDP estimated water loss when compared to load cell estimated water loss. Although TDP estimated water loss has been correlated with actual tree water loss for many species, these data suggest errors may arise when using TDPs to estimate water loss of small, containerized landscape tree species.