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The background for the monitoring of Danish Orchids

Home | Survey of orchids

Table of contents
  • Introduction
  • Number of species
  • Monitoring methodology
  • Results
  • Orchids are legally protected
  • Assessment of orchid species in Denmark
  • Census of flowering individuals
  • Rejuvenation
  • Immigration
  • Orchids and fungi
  • Ecology
  • Ways of living
  • Pollination
  • Variation in number
  • Additional reading on Danish orchids

  • Cephalanthera rubra (L.) Rich.
    Red Helleborine      

    Introduction (Table of contents)
    In 1982 Danish regional councils commenced a regularly annual census of selected orchid population. This initiative promoted the Danish Forest and Nature agency to initiate a joint programme for Monitoring of Danish Orchids. NERI took over the managing and co-ordination of the programme in 1994. During its lifetime approx. 300 populations have been monitored continuously or partly throughout the years. Monitoring of some population has stopped because their sites have disappeared for instance due to natural soil erosion, or it has been impossible to find the field marks again, or because the species in question has moved outside the sample area. A population may also disappear due to human impact e.g. digging.

    Number of species (Table of contents)
    The survey of orchids comprises 45 wild Danish orchids of which six are considered subspecies or variants. Three of the 39 species have become regionally extinct: Frog orchid (Coeloglossum viride), Autumn lady's tresses (Spiranthes spiralis ) and Military orchid (Orchis militaris).

    Monitoring methodology (Table of contents)
    Monitoring normally takes place once a year in the blooming season of the orchids. Depending on the species the blooming season normally starts in May, continues in June and July and end up in August. Volunteers interested in following the trend in the orchid populations, employees at the regional councils and the state forest perform the surveillance. The monitoring takes place in most parts of Denmark.

    A small number of populations of the more common species is monitored. On the other hand most or all populations of the rare species (species growing on 10 sites or less) are focused at the censuses.

    The practical part of the monitoring is a two step process. 1) The number of flowering shoots and if possible also the number of non-flowering is counted to deter the size of the total population of the species in question. In certain years counting has not been possible, as the specimens have remained subterranean. 2) An assessment of the living condition for the orchid in question on the site is performed. Some of the following species dependant features are examined: Is the site grazed? Is the grazing pressure convenient? Do a change in the ground water level occur? Is the site overgrown with trees and shrubs? Are there any visible changes on the site compared to last year's surveillance?

    The collected information is sent on pre-prepared forms to NERI that is responsible for the publishing of the Monitoring of the Danish Orchids homepage.

    Results (Table of contents)
    When an international name in the Survey of orchids is activated a list of Danish names on the site where the specific orchid is monitored appears. A histogram of the yearly census will appear on activation of a site name. The columns in the histogram show the yearly number of flowering shoots during the period of time where NERI has information in store. When information is available the number of vegetative shoots is displayed, too.

    Gaps in the time series are caused by lack of the yearly census or because the particular species has remained subterranean. Thus no aerial shoots can be counted.

    Orchids are legally protected (Table of contents)
    All Danish orchids are legally protected. The protection implies that everyone is free to study, draw, or photograph the orchids in nature; they must however be untouched. It is forbidden to damage, prick or dig the specimens, and it is prohibited to collect seeds from orchids outside gardens, parks, cemeteries, nurseries etc. The protection of orchids is laid down as a general protection, because many of the more rare and threatened species can be mistaken for the more common ones, and also because many Danish orchids are threatened. The protection is also a consequence of the Danish ratification of the Berne Convention, which aims to protect European species of wild plant and animals in their habitats. The convention emphasizes the protection of threatened species. Besides, two Danish orchid species are included on the EC Habitatdirective causing that the species and their habitats need strong protection.

    Assessment of orchid species in Denmark (Table of contents)
    An assessment of the species is based on the present distribution and the population number and fluctuations. Some species are widely distributed and found in most parts of Denmark. Others have only one or a few sites. The distribution in Denmark has been divided into the following regions: Northern Jutland, Western Jutland, Eastern Jutland, Southern Jutland, Funen, Lolland, Falster, Møn, Zealand and Bornholm. The number of sites present expresses the relative frequency of the species.

    The Red List assessment 2003 of the orchids is included and the international abbreviations for the Red List categories are used. A link to the Danish Red Data Book has been established where the construction of the IUCN Red List System is explained.

    Census of flowering individuals (Table of contents)
    The sexual reproductive organs of the vascular plants are located in the flowers. The stamens (the male organs) and the ovary (the female organ) are places in the same flower in all orchid species found in Denmark. Self-fertilisation is prevented by separation of the male and female organs in the flower. Thus, fertilisation is performed by e.g. bees, butterflies, moths, and hummingbirds in the tropics. Many orchids produce nectar that tempts the pollinators when the flowers are ready for fertilisation. The result of the fertilisation is seeds securing the species in the future.

    Flowering shoots are counted because 1) they carry the sexual organs of the specimens and produce the next generations wherefore they form an indirect measure of the relative reproduction rate of the population, 2) they provide a measure for the dispersal and size of the population on the sites even though there is no simple relationship between the number of flowering and vegetative specimens, and 3) they are often easy to count in a dense vegetation cover consisting of various species.

    All vegetative individuals must be counted if a measure of the propagation rate and the recruitment ability of the population are required. The counting of the vegetative specimens often demands great efforts and therefor time consuming, as the orchid leaves can be hard to distinguish from the surrounding vegetation cover or from the leaves of other orchid species growing on the same site. Finally, many juvenile vegetative shoots have a shorter growing season and wither earlier than the flowering ones.

    Rejuvenation (Table of contents)
    All Danish orchids are terrestrial compared to many tropical orchids that live as epiphytes in the canopy of the rain forest. Bog orchid (Hammarbya paludosa) and Fen orchid (Liparis loeselii) form an exception from the terrestrial pattern as they can be considered as epiphytes, growing in the top of the sphagnum and bryophyte layer in bogs and fens.

    Terrestrial orchids have underground parts functioning as storage organs. Besides, they give rise to next year's aerial shoots. When the new aerial shoot starts developing the shrunken remnants of the old organ decompose. A vegetative division of the underground part can occur resulting in formation of two or more separate plants.

    The underground parts are formed by different parts of the orchid plant. The rootstock is an underground stoloniferous stem or a rhizome that can grow either horizontal or vertical. The tuber is a swollen part of the root and is either entire or lobed. The entire tuber is ovoid or globose in shape, while the lobed is palmate, flat and long-digitate or spindle-shaped in outline. The pseudobulb is formed by swelling of the lowest part of the aerial stem and is connected to the epiphytic life form. The table shows the dispersion of the 39 Danish orchid species.

    No. species21621

    Immigration (Table of contents)
    The Danish orchids are all natives as they have dispersed to Denmark without human assistance. A comparison with other Danish plant families of similar size shows that the Orchids are the only family without introduced or adventive species in Danish nature. An organism is adventive when it has spread passively to a country outside its natural range either by the help of human transportation e.g. by car, train or ship. Most native species have presumably immigrated step by step with the development of the landscape that succeeded the withdrawal of the icecap after the last glaciation approx. 15.000 years ago. Two species, Lesser twayblade (Listera cordata) and Creeping lady's tresses (Goodyera repens), have immigrated lately and was first recorded in the 1800 century and 1878, respectively. Their late arrival in Denmark must rely on the first hand on the plantation of conifer trees.

    The ongoing intensive field investigation of Denmark and the scientific research are the main reasons for the improvement of the number of Danish orchid species. Danish examples are Violet helleborine (Epipactis purpurata) recognised in 1953 and Dactylorhiza baltica discovered in 1997. Both species have undoubtedly grown in Denmark before the years mentioned.

    Orchids and fungi (Table of contents)
    Most of the 39 Danish orchid species have chlorophyll and produces plant nutrients and building substances by photosynthesis. Three species, Ghost orchid (Epipogium aphyllum), Coralroot orchid (Corallorhiza trifida) and Bird's-nest orchid (Neottia nidus-avis), lack chlorophyll nearly or entirely. The needs for nutrients are covered by close symbiosis with subterranean fungi. The symbiosis causes that especially specimens of the three species have a fungi-like living pattern. They have the ability to stay subterranean for one year or more and meanwhile regenerate the rootstock enable the specimen to raise aerial flowering shoots again. Besides, the Bird's-nest orchid can form subterranean, self-fertilising flowers directly on the rootstock.

    The 36 other orchid species that produce organic substances by photosynthesis have a complicated symbiosis with soil fungi, too. The result is that many species are more or less specialised in their choice of habitat. Therefor it is often hard or even impossible to move an orchid from one location to another. The sensibility to additional amounts of nutrient and pesticides of the co-operating fungus often causes that the corresponding orchid species is sensible, too.

    The presence of fungi has an impact on the possible propagation success of the orchids. The orchids produce the smallest and lightest seeds in the Plant Kingdom as they are formed without endosperm. In case of the Fragrant orchid the weight has been measured to 0,000008 grams.

    On germination the orchid seed depends on the presence of adequate fungi supplying the sprouting orchid with proteins. The sprouting orchid and the fungus join in a little bulb-shaped or worm like stolon whose outer layer is penetrated by the mycelium of the fungus, the protocorm. It may last years before the emergence of adventitious roots and aerial stems from the protocorm. Therefor there is time gab between germination of the seed and the first flowering of the new orchid. The first green leaves appeared after four years in cultivation experiments on the germination of seed of the Fen orchid (Liparis loeselii).

    Ecology (Table of contents)
    Some orchid species have adapted to live under the specific edaphic conditions by which the corresponding fungus partner thrives. Other orchid species have a wider ecological range and is therefor found in various vegetation types; a few orchids are especially actively dispersing and able to grow in many habitat types even in places where the soil composition has been changed by agricultural management. A couple of species are able to colonise areas with thin vegetation cover due to soil erosion or excavation. Examples of colonising species are Fen orchid (Liparis loeselii), Dactylorhiza purpurella ssp. majaliformis and Marsh helleborine (Epipactis palustris). A general feature of the habitats of the Danish orchid species is a demand for unfertilised and unsprayed conditions. Super-fertilised fresh water in a neighbouring ditch caused the decaying of the tubers of the Fragrant orchid (Gymnadenia conopsea) on its last site on Funen in the 1990es.

    A dispersion of Danish orchids according to preferred nature type 12 may be considered as forest orchids, 13 as fen orchids and 9 as dry grassland orchids. The remaining 11 are less habitat specific as they can be divided into more categories.

    Ways of living (Table of contents)
    The height of the full-developed specimens varies between a few centimetres to approx. 1.5 metres; the smallest specimens are found among Bog orchid (Hammarbya paludosa) and Musk orchid (Herminium monorchis), while the tallest are the Helleborine species (Epipactis sp.). Some species especially among the fen, dry grassland and heath orchids demand light and suffer from overgrowing from dense vegetation, shrubs and trees. On the contrary, many woodland orchids, e.g. the Helleborine species, are adapted to various amounts of shade. The chlorophyll-less orchid species are able to accomplish their life cycle in deep shade in willow-shrubs or closed beech-forest.

    Pollination (Table of contents)
    Most Danish orchids fertilise by cross-pollination. Many species have developed complicated pollination mechanisms to prevent self-pollination, while some species depend on self-pollination. In a few species both pollination mechanisms are working: if cross-pollination fails self-pollination secures that fertilisation takes place.

    The sexual reproduction (i.e. the fertilisation takes place after preceding pollination) is by many species the most important source to seed dispersal on the entire site and in some instances the only source for long-distance dispersal. Besides, some species are able to spread on the sites by vegetative propagation by forming subterranean stolons or by division of the rootstocks. In the tuberous orchids division of the tuber performs vegetative propagation. Other organs than the subterranean can perform vegetative propagation in the orchids. The only Danish example is the Bog orchid (Hammarbya paludosa) forming bulbils from the leaf tips.

    Variation in number (Table of contents)
    The regulation mechanisms behind the population fluctuations are only scanty known. It is a fact, that a dry spring season versus a wet has an influence on the population number of flowering shoots. Spring arrived early in Denmark in 1992 and stayed dry; the number of blooming orchids on dry grassland sites was specifically lower that year compared to the previous. On the other hand many orchids were in bloom in springtime in 1994 and 1995 after mild winters rich on precipitation.

    Another prominent feature is the human impact - conscious or unconscious - on the habitats of the orchids. The choice of browsers, their number and sort, the time for mowing, the supply of fertilisers, the degree and type of forest management, and human trampling on the sites are all impacts that influence the composition of the vegetation cover and therefor the living conditions of the orchids. Besides, the genotype of the species in question plays an important but unknown part for the germination, for the frequency of flowering, the setting of fruits, and for the life span of the individual specimen. Add to this the symbiosis with fungi whose impact on the life cycle of orchids is generally speaking unknown apart from investigations carried out in laboratory on the relationship between fungi and the seed germination of the orchids.

    Additional reading on Danish orchids (Table of contents)

    NERI publications

    Wind, P. 2002: Bevaring af Mygblomst (Liparis loeselii (L.) L.C.M. Richard) i Danmark. - Flora og Fauna 108: 33-48. In Danish with a summary in English Download i pdf-format (25223 kb).

    Wind, P. 2002: Overvågning af orkidéer 2000. Arbejdsrapport fra DMU nr. 163. 46 sider. Download i pdf-format (634 kb). Kan købes i Frontlinien. Pris 50 kr.

    Wind, P. 2001: Overvågning af danske orkidéer 1999. Danmark. Naturovervågning. - Danmarks Miljøundersøgelser. Arbejdsrapport fra DMU nr. 144. 114 sider. Kan købes i Frontlinien. Pris 65 kr.

    Wind, P. 1999: Overvågning af danske orkidéer 1998. Påvirkningsfaktorer. Danmark. Naturovervågning. Arbejdsrapport fra DMU nr. 109. 31 sider. Kan købes i Frontlinien. Pris 65 kr.

    Other publications

    Delforge, P. 1995: Europas Orkideer. Oversat og bearbejdet af J. Feilberg. - Gad. København.

    Johnsen, B. 1994: Skandinaviens orkideer. - Rhodos. København.

    Løjtnant, B. 1991: Overvågning af Orchideer 1987-89. - Flora og Fauna 97: 63-121.

    Nilsson, S. & Mossberg, B. 1979: Nordens orkideer. Dansk udgave v. B. Løjtnant. - Gyldendal. København.

    Rasmussen, H.N. 1995: Terrestrial orchids from seed to mycotrophic plant. - Cambridge University Press. Cambridge.

    NERI P.O. box 358 Frederiksborgvej 399 4000 Roskilde  Denmark Tel: +45 4630 1200 Fax: +45 4630 1114
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