Population dynamics and life-history ofCoeloglossum viride(L.) Hartm.: an endangered orchid species in The Netherlands

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Abstract
Coeloglossum viride (L.) Hartm. has a worldwide distribution in the Northern hemisphere where it can be found in a broad range of habitats; it is not, at present, threatened with extinction. However, in several European countries there has been a dramatic decline in sites occupied by this orchid. In The Netherlands only 2 populations remain of 55 extant before 1950. Knowledge of its ecology and life history are necessary to preserve this species at sites not directly threatened by habitat destruction. The results of a 7 year demographic study of a population of C. viride in The Netherlands are presented. Annual recruitment and mortality vary considerably from year to year, whereas the flux in individual plants is always high. The half-life of the cohorts varies from 1.0 to 2.4 years and is on average c . 1.5 years. This indicates that C. viride is a short-lived terrestrial orchid species. The number of flowers per inflorescence varies from 2 to 26 per spike. The mean flowering percentage in the population is rather high (50%), while the fruit production was low in the year this was recorded (1994), viz. c . 10%. The average number of seeds per capsule was c . 2300. Plants emerging above ground for the first time are already able to produce an inflorescence, and the average number of flowers equals those of plants initially passing a vegetative life phase for one or more years. Dormancy is a rare phenomenon in this species and the absence above ground when it does occur does not last longer than one growing season. Vegetative multiplication plays a minor role in population dynamics. The studied population is likely to be in a healthy state: there is a high recruitment almost every year resulting in a vigorous age structure. Management of the site, with mowing in July following seed dispersal and sheep grazing in winter is beneficial. The absence of intentional fertilization is a condition for a suitable, low vegetational structure of the sward during the growing season of this species.

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