Escuela Practica: an introduction to vegetation sampling using computer simulation

Abstract

The fact that vegetation varies from location to location and with time is common knowledge. The description of this spatial and temporal variation, or pattern, is a prelude to seeking an ecological explanation for the observed variation. It is essential, therefore, that students in ecology receive a grounding in the methods used to describe vegetation. The elements of vegetation description are outlined in any of the large number of available standard texts (e.g., Greig-Smith 1983; Causton 1988). These elements include sampling design, measures of plant abundance, type of distribution, identification of association between species, and the scale of any observed pattern. Prior to 1987 third year plant ecology students at The University of Western Australia were given their introduction to the methods of vegetation description in the field. A set of four artificial populations were occasionally used in the laboratory, principally when the weather was too wet for field work, to illustrate the effects of plant distribution and quadrat size on estimates of frequency and density. It was found that these exercises offered several advantages over conventional field work. Compared with the field work they could be completed relatively quickly; the students did not have to cope with problems of species identification; and, because they were able to compare their sample estimates with the known parameters of the artificial populations they had greater confidence in the methods being demonstrated. In 1987 the four artificial populations were designated as separate species and combined into a single map. To introduce more variation additional species exhibiting a range of distributions (random, clumped and regular) and associations (positive, independent, and negative) were added. In an attempt at further realism separate overlays were generated containing information representing soil type and topography. Students were now able to investigate not only aspects of vegetation description but the next ecological step of how the discovered species patterns might be related to abiotic factors of the environment. An Apple University Development Fund award in 1990 of $3000 enabled the transfer of the map information to the Macintosh microcomputer format.