Drought in forest understory ecosystems – a novel rainfall reduction experiment

Abstract

Abstract. Precipitation patterns across Central Europe are expected to change over the 21st century due to climate change. This may reduce water availability during the plantgrowing season and hence affect the performance and vitality of forest ecosystems. We established a novel rainfall reduction experiment on nine sites in Germany to investigate drought effects on soil-forest-understory ecosystems. A realistic, but extreme annual drought with a return period of 40 years, which corresponds to the 2.5 % percentile of the annual precipitation, was imposed. At all sites, we were able to reach the target values of rainfall reduction, while other important ecosystem variables like air temperature, humidity, and soil temperature remained unaffected due to the novel design of a flexible roof. The first year of drought showed considerable changes in the soil moisture dynamics relative to the control sites, which affected leaf stomatal conductance of understory species as well as evapotranspiration rates of the forest understory.

Characteristics of Fine Roots of Pinus massoniana in the Three Gorges Reservoir Area, China

“…However, there was a significantly positive correlation between fine root decomposition rate and soil temperature, which was, therefore, the major driver of fine root decomposition, similar to that found in previous studies [57,[62][63][64][65][66]. According to Cusack et al [62], precipitation-related parameters are strong predictors of litter decomposition in neotropical forests, and Hobbie et al [67] also suggested that moister soils could facilitate rapid mass loss by promoting leaching and microbial activity or a faster colonisation of decomposing material by microbes.…”

Does drought alter hydrological functions in forest soils?

“…In our rainfall exclusion experiment drought stress was not intense enough to induce mortality or strong changes in aboveground biomass of a particular species (Gimbel et al, 2015). Nevertheless, drought and water repellency may promote the die-off of fine roots, which thereupon contribute to the total organic matter in the soil.…”

“…The resulting annual target precipitation inputs under the roofs were 700 mm (26 % reduction) for Schwäbische Alb, 355 mm (33 % reduction) at the Hainich-Dün and 395 mm (27 % reduction) at the Schorfheide-Chorin site. For a more detailed description of the whole experimental drought setting and of the study plots see Gimbel et al (2015).…”

“…The experiments of this study are part of the interdisciplinary project "Global Change Effects on Forest Understorey: interactions between Drought and Land-use Intensity" (Gimbel et al 2015). The artificially imposed drought was created by a 10 m × 10 m roofed subplot, covered with transparent panels.…”

“…By introducing these extreme events, the question of transferability of the results to natural systems in respect to the expected behavior under predicted future drought conditions arises. Therefore, this study employs a moderate rainfall reduction equivalent to an annual drought with a 40-year return period, in accordance to climate predictions, thereby avoiding tentativeness due to an overreaction to an unnatural extreme drought (Gimbel et al, 2015).…”