L. De Lange

TDR calibration of organic forest floor media

Abstract We carried out a time domain reflectometry (TDR) calibration for 25 forest floor samples of five different forest stands. Linear regression was used to estimate the volumetric water content from the refraction index. Due to the presence of bound water, it was impossible to predict the calibration line parameters from theoretical values with a refractive mixing model. However, when the apparent dielectric constant of the water was considered, it was possible to predict the offset parameter because the low forest floor bulk density caused the calibration line slope and offset to be almost reversely proportional. Calibration parameters for different forest floor materials are presented. Allowing a somewhat higher margin of error we could also establish general calibration curves which were in close agreement with a published calibration curve (Malicki et al., 1994). An error analysis showed that decomposition of organic matter, residual water and temperature effects have negligible effects on the calibration parameters. Shrinkage of the organic material significantly influenced both the volumetric water content and the TDR reflection times. If not corrected, both effects yielded systematic errors of approximately 0.02 cm3 cm−3 for a strongly shrinking H horizon.

Gibbosity in the complex Lemna gibba/Lemna minor: Literature survey and ecological aspects

Abstract The status of the morphologically intermediate strains between Lemna gibba and Lemna minor is discussed.

A system for the evaluation of aquatic biotopes based on the composition of the macrophytic vegetation

Abstract A system for the evaluation of aquatic biotopes from a biological point of view, based on the stands of macrophytic vegetation, is proposed. It consists of a structural part, based on the percentage cover per vegetation layer, the number of species and the quantity of filamentous algae, and a floristic part, based on the rareness of the species present. Some examples of application of the system are described.

Survey of the macrovegetation in a ditch near Tienhoven (Utrecht, the Netherlands)

This survey was carried out in the framework of a study of various components of the ecosystem of a ditch, which was selected for this purpose because of its rich and varied botanical aspect. On the basis of the physiognomic differentiation in the macrovegetation in the course of its length, 6 sections were discerned. The sections differed moreover in their dimensions and differences in chemical composition of the water were supposed, local connections with a village ditch receiving sewage water (section l) and with a side ditch from a weekend resort (section 2) being present. This last section was divided in two longitudinal subsections (2 south and 2 north) because of a different vegetation aspect, probably caused by ditch cleaning of the southern half in last autumn, whereas the northern half had not been cleaned in the last 2 years. (see also BELTMAN, 1976).

Report of a vegetational survey of the Island of Elba, Italy

Abstract During a botanical excursion to the island of Elba, Italy, in April 1968, a vegetational survey on a physiognomic basis, covering the whole island, was carried out with the aid of a number of students, and the results were subsequently mapped. Details of the methods used are given and some aspects concerning the legend units of the vegetation map are discussed.