Disturbance in ecosystems

The importance of  disturbance for vegetation dynamics as well as for stability of successional stages

Disturbances strongly affect ecological systems and are often responsible for the maintenance of dynamic stability and the persistence of biodiversity. Disturbances occur across a wide range of spatial and temporal scales, and on all levels of ecological organization. Concepts of vegetation or ecosystem dynamics, therefore, need to include disturbance as a driving force for pattern formation. Additionally, humans often strive to alter disturbance regimes. The assessment of disturbance impact and the development of models with predictive capabilities require an operational method to describe disturbances, to understand disturbance dynamics, and to identify the significance of disturbance regime in various ecosystems. Recognition of relationships between dimensions of disturbance events and dimensions of system response is the key for detection pattern resemblance of various disturbances on proportionate scales (from Jentsch 2001).

small scale disturbance by rabbits       small scale water erosion

 

In a recently finished research project in dry acidic open grassland vegetation we tested the following hypotheses:

  1. The diversity of cases interrelation disturbance regime and ecosystem dynamics can (i) be characterized by the interactions of a few fundamental variables and (ii) be addressed for generality across various disturbances and ecosystems by relating dimensions of disturbance events to dimensions of ecosystem response

  2. Stability of dry acidic grassland vegetation on inland sand dunes is a function of (i) small-scale disturbance and (ii) resource availability (free substrate, seed source, water and nutrients)

As a result of small-scale ground disturbance, successional pathways and plant community patterns in dry acidic grasslands on inland sand dunes are continuously altered and reorganized in composition, velocity and trajectory, especially with superimposed varying environmental conditions, such as increased aerial nitrogen deposition, global warming or species invasion.

This context was addressed by conducting experimental soil disturbances along a productivity gradient within primary successional stages of dry acidic grasslands dominated by Corynephorus canescens (L.) P. Beauv. On inland sand dunes. Relationships between disturbance intensity, soil nutrient availability, presence of belowground seed sources and vegetation response regarding species richness, plant functional groups and re-colonization processes were investigated and integrated. Up to now, it became very clear that repeated small-scale disturbances are essential for the stability of the primary successional stages.

       

Figure: Disturbance experiment at a field site near Erlangen in order to  assess the role of various soil disturbances for the vegetation dynamics in open acidic grasslands. a) schematic representation of the experimental design (H = Hieracium dominated site; P = Polytrichum dominated site; C=Corynephorus dominated site; L = lichen dominated site R = ruderal site) b) in situ plots at the Hieracium dominated site

 

Descriptive Research: Digital photography is employed for a quantitative documentation of frequency, intensity and spatial extension of small scale soil disturbance events in open sandy habitats.

Digital photographs of vegetation patterns in open acidic grasslands and their and quantitative evaluation

Figure: Digital photographs of vegetation patterns in open acidic grasslands and their and quantitative evaluation

 

Experimental Research: In situ disturbance experiments are carried out at a former military training area near Erlangen in cooperation with the Geobotany group of the University of Erlangen and Dr. A. Jentsch from the Environmental Research Center (UFZ) Leipzig. Since dry acidic grasslands contain a high proportion of endangered species, this research has quite a few applied aspects and the results are already being used in several environmental protection projects within the “Sandachse”-Project of the State of Bavaria  (Ph.D. Thesis Jentsch), In an ongoing research project we are presently analyzing the importance of socalled "functional groups" for the stability of the various successional stages (see page of S. Friedrich).

 Management measure for the conservation of Corynephorus canescens: Anthropgenic disturbance

Figure: Management measure for the conservation of Corynephorus canescens: Anthropgenic disturbance

        

Figure: Experimental plots where certain functional groups were removed. a) schematic representation of the experimental design b) in situ plots

 

Publications:

Beyschlag, W., Jentsch, A. Weigelt, A. (2002) Ökologische Grundlagenforschung und praktische Naturschutzarbeit in Sandlebensräumen – Konfrontation oder Kooperation? Naturschutz und Landschaftsplanung 34: 82-88

JENTSCH, A., BEYSCHLAG, W., NEZADAL, W. (2002) Bodenstörungen - treibende Kraft für die Vegetationsdynamik in Sandlebensräumen: Naturschutz und Landschaftsplanung 34: 37-44

JENTSCH, A., FRIEDRICH, S., BEYSCHLAG, W., NEZADAL, W. (2002) Significance of ant and rabbit disturbances for seedling establishment in dry acidic grasslands. Phytocoenologica 32: 553-580

 

JENTSCH, A. BEYSCHLAG, W. (2003) Vegetation Ecology of Dry Acidic Grasslands in the Temperate Zone. Flora 198: 3-25

WHITE, P.S., JENTSCH, A. (2001): The search for Generality in Studies of Disturbance and Ecosystem Dynamics. In: Esser, K., Lüttge, U., Kadereit, J.W., Beyschlag, W. (eds) Progress in Botany Vol 62; Berlin, Heidelberg, New York (Springer); pp. 399-450

JENTSCH, A. (2001): The Significance of Disturbance for Vegetation Dynamics. A Case Study in Dry Acidic Grasslands. Doctoral Thesis, University of  Bielefeld, 199 p.

JENTSCH, A., BEYSCHLAG, W., NEZADAL, W. (2001): Bitte Stören! Vegetationsynamik in Sandlebensräumen. In: Forschung und Naturschutz in Sandlebensräumen. Tagungsband Erlangen, pp. 50-53

BEYSCHLAG, W., JENTSCH, A., STEINLEIN, T. (2001): Experimental investigations on the role of soil disturbance in sandy habitats. Verh. Ges. f. Ökologie 31: 95