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Partitioning of the available energy at the Earth's surface into the latent heat (LE) and sensible heat (H) fluxes has important climatological, hydrological, and physiological implications. With the prediction of more frequent droughts in central Europe in the near future, there is a particular need to understand variability in available energy partitioning under drought stress conditions at forest ecosystems that are common in the region, such as Norway spruce and European beech. Using eddy covariance measurements from two Norway spruce sites with contrasting wet and dry climates and one European beech site in the Czech Republic, it was found that the proportion of energy partitioned into H was greater at the spruce sites than at the beech site in all conditions during the growing season. The difference between the mean midday (09:00-15:00) ss values for low stress conditions and drought stress conditions was much smaller at the European beech site (ss = 1.04 vs. 1.11) than at the wet (ss = 1.52 vs. 2.50) and dry Norway spruce (ss = 1.80 vs. 2.70) sites, indicating that ss was not as sensitive to drought stress at the European beech site as at the Norway spruce sites. The high ss values and enhancement of drought conditions through positive feedback processes at Norway spruce stands mean that the potential substitution of Norway spruce monocultures with mixed broadleaf-coniferous stands in central Europe will likely lessen the severity of droughts and heat waves in the region.

Plain Language Summary Partitioning of the available energy at the Earth's surface into the latent heat and sensible heat fluxes plays an important role in processes such as variability in the height of the convective boundary layer and associated weather processes. With the prediction of more frequent droughts in central Europe in the near future, there is a particular need to understand how available energy partitioning varies under different environmental conditions at forest ecosystems that are common in the region, such as Norway spruce and European beech. Using eddy covariance measurements from two Norway spruce sites with contrasting wet and dry climates and one European beech site, it was found that the proportion of energy partitioned into sensible heat was greater at the spruce sites than at the beech site in all conditions during the growing season. The partitioning of available energy was more sensitive to drought stress at the Norway spruce sites than at the European beech site. The high sensible heat fluxes at Norway spruce plantations during drought conditions means that the potential large-scale substitution of Norway spruce monocultures with mixed broadleaf-coniferous plantations in central Europe could lessen the severity of droughts in the region.