From the introduction:
"The growing "popularity" of European orchids and the democratization of their study in the past decades had a serious impact on the number and diversification of the orchid literature. Population dynamics of orchids, the study of the development and behaviour of orchid populations with time, is one of the aspects that receive more attention nowadays. This phenomenon might reflect the generally increased concern for the conservation of natural habitats and endangered species.
With serial observations on the size of orchid populations I denote all kinds of publications, from very professional, mostly demographically orientated analyses to very simple reports on the annual size of a population in two consecutive years. As a framework for comparing my own observations on Dactylorhiza praetermissa populations (Vanhecke 1985, 1988, 1991), I am compiling relevant literature in this field of research. These data were for the first time summarized in a synoptic comparative table made in 1991 (unpublished, in Dutch, intended for internal use only).
This original table was based on papers published until 1990 (with a few exceptions, however: some papers published in 1991, but that were available to me before their publication, were incorporated). Only European literature was taken into account. The reason for this is that already a virtually complete general bibliography exist of the European orchid literature (B. Willing & E. Willing 1977, 1985; E. Willing 1984-1991: semi-annual contributions in the Mitteilungsblatt Arbeitskreiss Heimische Orchideen Baden–Wüttemberg and the Berichte aus den Arbeitskreisen Heimische Orchideen). Even under these privileged conditions it showed rather difficult to gather all concerned publications since many were published in small, very local journals. It seemed impossible to me to start collecting in the same way papers from other continents, even without having the slightest idea of what already exists, on species that I do not know.
From the beginning the concept of this compilation work had two major objectives: (1) bringing together as much publications as possible which at least partially deal with fluctuations of the size of European orchid populations and (2) to standardize the information contained in these publications in order to make it possible to compare the available data. Therefore each publication was screened on a number of technical characteristics of their data concerning population dynamics, such as:
- the identity of the taxon(a) studied;
- the number of populations studied per taxon;
- the length of the longest uninterrupted series of observations;
- the total number of observation years;
- the overall length of the observation period(s);
- the size (maximal, minimal and average) of the studied population(s) during the total observation period.
The combination of these descriptive variables permits the user of the table to get a fairly good idea of the information contained in the cited papers. However, no effort was made to summarize or discuss the proper results mentioned in these papers, so that the reader is obliged to consult the cited literature.
In total this first synoptic table contained information from 58 publications of 56 authors on the pluri-annual observation-series of 184 populations of 41 orchid taxa (39 species and 2 interspecific hybrids). Some aspects of a global analysis of this original table were presented at Nijmegen (September 26th, 1992), on the occasion of Eurorchis 92, an international symposium on European orchids. The paper corresponding to this technical synthesis is in print (Vanhecke 1993).
After 1990 some important new papers and books (e.g. Wells & Willems 1991) concerning the study of the dynamics of European orchid populations were published, so it seemed appropriate to actualize the data of the original table and at the same time to broaden its potential use by translating it into English. No major changes in the concept of the table were introduced, but in order to gain maximal information on the population dynamics of European orchids, a single important publication, dealing with non European populations of Epipactis helleborine (Light & Macconaill 1991), was included.
In total 70 entirely new series of observations on the size of European orchid populations were added to the table, most of them (61) extracted from two publications. In addition to those, 26 "incomplete" series, dealing with transplanted (or sown) populations in a specially created orchid garden, are given. These last series are called incomplete because during the establishment of these species intentional introduction took place at several occasions and it is necessary to consult the original papers to be informed on all details. Eight more taxa had to be added to the first list, among them six new species, two interspecific hybrids and one intergeneric hybrid (one of these six species and the three hybrids belong to the group of transplanted orchids). On several populations, new observations continuing already familiar series, were published."