dataset: Responses of the structure and function of the understory plant communities to precipitation reduction across forest ecosystems in Germany

Context: Understory plant communities play a central role in forest biogeochemistry and the recruitment of trees making up the future forest. It is so far poorly understood how climate change will affect understory structure and functions in forest of different management intensity.

Aims: We monitored understory functional traits including transpiration and carbon isotope discrimination, community structure and diversity during two growing seasons as affected by drought in forests subjected to different management intensities. We hypothesized that drought would affect ecophysiological traits such as transpiration but not species richness and diversity. Moreover, we assumed that stand-specific characteristics and forest management intensity modify the drought-resistance of the understory community.

Methods: We set up roofs in beech and conifer stands with different management intensity in three different regions across Germany and a drought event close to the 2003 drought was imposed in two consecutive years.

Results: Precipitation reduction decreased soil water content by 2 to 8%, depending on stand and region, in comparison to the control subplots. In the first year, leaf level transpiration was reduced for different functional groups, which scaled to community transpiration modified by additional effects of drought on functional group specific leaf area. Acclimation effects in most functional groups were observed in the second year. We did not observe a significant reduction of plant diversity or a consistent management effect upon drought.

Conclusion: Our results indicate high plasticity and acclimation responses of the forest understory vegetation to changing climate conditions and recurrent drought events.

Abbreviations:

sp12 - campaign spring 2012; ls12 - campaign late summer 2012; es13 - campaign early summer 2013; ls13-campaign late summer 2013

SEW16 - Schorfheide plot 16; SEW49 - Schorfheide plot 49; SEW48 - Schorfheide plot 48;HEW03 - Hainich plot 03; HEW12 - Hainich plot 12; HEW47-  Hainich plot 47; AEW13 -  Alb plot 13; AEW29 - Alb plot 29; AEW08 -  Alb plot 08
explo - exploratory
SEW - Schorfheide; HEW - Hainich; AEW - Schwäbische Alb
in - conifer intensive managed; ma - beech managed; un - beech unmanaged
c- control; r - roof
LAIs - community leaf area index m²/m²; H - Shannon´s diversity index; Ts - community transpiration rate (weighted by LAI) mmol H₂O m-² leaf area s-¹; Ets - Evapotranspiration (mmol/m2/sec); E - Evaporation (mmol/m2/sec); C - leaf photosynthetic carbon isotope discrimination (∆¹³C) according to Farquhar et al. (1982); Cs - community photosynthetic carbon isotope discrimination (∆¹³C) according to Farquhar et al. (1982) (weighted by LAI)