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Abstract "Heft 44"

Freiburger Bodenkundliche Abhandlungen

Schriftenreihe des

Institut für Bodenkunde und Waldernährungslehre

der Albert-Ludwigs-Universität Freiburg i.Br.
Schriftleitung: P. Trüby

Heft 44

Nicole Wöhrle

Randomisiert wandernde Messplots.
Raum-Zeit-Modellierung von Parametern des Stoffhaushalts in heterogenen Kalkbuchenwäldern

Freiburg im Breisgau 2006

ISSN 0344-2691


Assessment and modelling of spatial heterogenity of matter budgets in forest ecosystems poses a particular challenge to  ecosystem studies.  Parameters of matter flux are often measured at only a few fixed points and with a high temporal resolution for practical reasons. Thus, high spatial variability is often not taken into account.

Many matter flux parameters are controlled by external driving forces such as temperature. Based on this observation, the "randomized moving plots" (RMP) sampling design uses time series of such "global" variables to model temporal dynamics. The measurement capacity set free by this method is re-invested in the assessment of spatial variability of matter flux. Measurements are taken at a few points over a short period, after which the sampling equipment is moved to new locations. Using spatial statistics, remaining residues of the global model at RMP-sites are analyzed for spatial patterns caused by site factors such as crown structure.

This new approach was tested in a Fagus sylvatica forest ecosystem on limestone. Samples were taken on both north-eastern and south-western exposed slopes, with two different silvicultural treatments each, a control lot without thinning and a thinned lot with half the trees cut (each lot approximately 0.5 ha). Over a period of three growing seasons, measurements were taken with three RMPs in each silvicultural treatment. These were moved biweekly, so that in the end about 90 points in each lot were available for interpretation. Meteorological towers situated on both slopes provided meteorological parameters in a high temporal resolution. Conventionally equipped stationary plots were installed as a reference on each slope. Information about the crown structure was derived from airborne laser scanning data.

With the help of time series analysis it was shown that the temporal dynamics of different parameters of matter flux are highly correlated with the time series of global variables, especially air temperature, global radiation, precipitation and potential evapotranspiration. This is also true for the chemical composition of seepage water at the calcareous investigation site. This confirmed that temporal variation can be derived from time series of the main driving forces.

By analyzing the residues of the temporal model it was possible to make statistically robust distinctions between silvicultural treatments, based on water and soil temperature budget averages. These are valid for the entire examination area. The thinning lots had significantly higher throughfall precipitations and soil temperatures as well as higher soil moisture in the top soil.

The spatial distribution of throughfall precipitation showed small-scale spatial patterns. The identified ranges of spatial correlation from 6 to 15 meters are comparable to those achieved with elaborate studies based on fixed measurement plots. Comparisons with the mean crown density and crown structure map prove the impact of the crown structure on the spatial distribution of the throughfall precipitation. Patterns of spatial correlation for the soil temperature could be demonstrated as well, suggesting the crown structure´s influence. The point density of RMPs in this study was too low to reveal spatial patterns of the water potential.

The results of this methodological study show, that it is possible to make statistically robust statements about an examination area with different silvicultural treatments, at a low cost, based on six measuring devices per hectare. Additionally, results indicate that local driving forces can be isolated by increasing the RMP point density and that real time-space-modelling will be possible with the RMP-approach. However, further research is required regarding space-time-structures and the application of the RMP-method for modelling matter fluxes.
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