KROOF 1 Experiment - Throughfall Exclusion

The phase I of this project has been focusing on the effect of a long-term drought and species mixture on mature beech and spruce trees.

To realize a long-term drought, 12 experimental plots (144 m² size) with a species mixture of adult beech and spruce were chosen.

As early as 2010, narrow trenches were dug at the edges of the 12 experimental plots to a soil depth of 1 m, and thick plastic tarpaulins were pulled into the sides of the trenches to prevent root growth outside the plots and to interrupt the lateral flow of water across the plots (Pretzsch et al. 2016, Grams et al. 2021).

Each plot contains groups of 3-7 beech (approximately 90 years old) and spruce (approximately 70 years old) with pure stand zones (intraspecific competition) at the ends of each plot and an interspecific mixing zone in the middle of the plots (Figure 1a, see Goisser et al. 2016, Grams et al. 2021 for details).

Six plots were equipped with rain exclusion roofs (TE, Figure 1b). The other six plots were exposed to natural rainfall events as control plots (CO). The roofs were automatically closed during rain events throughout the growing season (from April to November) for five years (2014-2018) and opened during the winter months. Thus, ~70% of the annual precipitation was excluded. The crane placed next to the plots allowed measurements in sun-exposed canopies, such as measurements of leaf water potential and photosynthesis.