Population biology of the rare military orchid (Orchis militaris L.) at an established site in Suffolk, England

Abstract

In Britain, where it reaches the north-westerly limit of its European distribution, Orchis militaris L. is extremely rare. Well-established and persistent populations of 0. militaris are known to exist at only two sites. The largest extant population of 0. militaris occurs in a disused chalk pit in Suffok. A preliminary demographic analysis of this population, covering the period 1975 to 1991, along with estimates of key life stage transition probabilities are presented here. From 1975 to 1986 the number of separate identifiable plants in the population declined substantially. Until 1986 recruitment of rosettes was poor. The largest cohort of new plants, recorded in 1976, was 35. Approximately 48% of new individuals recruited between 1976 and 1985 failed to flower. Of those flowering, approximately 55% flowered during their first year above ground. Of the original population recorded in 1975, 67.8% flowered at least once during the study. The reproductive performance, i.e. the frequency of flowering and the period between episodes of flowering, varied considerably between individuals. Some plants flowered every year while others only flowered once during the study. Few plants remained below ground for more than one year, while several apparently persisted below ground for more than 6 successive years. Although the number of plants that can be identified as separate individuals has declined, the total number of rosettes in the population has, from 1986, increased dramatically. Because of the dense clumping of these recruits it is not possible to determine whether they are derived from seed or vegetative propagation. When post 1986 recruitment is combined with the number of plants that established before 1986 and survive, the apparent number of plants present at the site has more than doubled between 1975 and 1991.

Orchid Biology: Reviews and Perspectives, VIII

“…Each year an average of 12.5% (0-50%) of the population remained dormant, and only once (in 1984) did all plants appear above ground ( Wells and Cox, 1991). On the average nearly 14% of Orchis militaris plants were dormant during anyone year ( Waite and Farrell, 1998). The probability of dormancy did not depend on age (Hutchings, 1987b).…”

“…On average in 5 populations of Orchis ustulata, 22% of the plants which bloomed during one year also flowered during the subsequent one, 59% remained dormant and 19% were vegetative ( Fig. In Orchis militaris 40 to 52% of plants flowering in one year flowered in the next, 9 to 10% stayed dormant, 19 to 40% were vegetative and 3 to 18% died annually ( Waite and Farrell, 1998). The ratios in Ophrys sphegodes were 43, 19, and 24 (Waite, 1989).…”

“…Irregular patterns in flowering may be the result of the negative cost associated with sexual reproduction and leaf herbivory. This suggests that cost of flowering is very low because plants had enough resources for consecutive flowering ( Waite and Farrell, 1998). After flowering, 3 years were required for a Tipularia plant to develop the necessary leaf area to flower again.…”

“…For another species of the genus, 0. sphegodes, the average percentage of dormant plants during 10 years was approximately 50. Kull and Tuulik, 1994Gregg, 1991Willems and Meiser, 1998Gill, 1989Falb and Leopold, 1993Kull1995b Shefferson et ai., 2001Rydlo, 1995Kull and Tuulik, 1994Light and MacConaill, 1991Mehrhoff, 1989bWhigham and O'Neill, 1991Tamm, 1972Elveland, 1993Wells and Cox, 1991Hutchings, 1987; Waite and Hutchings, 1991Tamm, 1972Inghe andTamm, 1988 Hutchings, 1998; Waite and Farrell, 1998Willems, 1982Vakhrameeva and Denisova, 1988Vakhrameeva and Denisova, 1988Wells, 1967 In Epipactis helleborine a quarter to half of the population emerged in any given year ( Light and MacConaill, 1991). On the average nearly 14% of Orchis militaris plants were dormant during anyone year ( Waite and Farrell, 1998).…”

“…In most cases the risk of death remains constant over time. Willems and Meiser, 1998 Ophrys api/era 5.8-11.2 (6.6) Wells and Cox, 1991 Ophrys sphegodes 1.5-2.3 (l.9) Hutchings, 1987b Orchis militaris 2.2-7.8 (4.8) Waite and Farrell, 1998 Spiranthes spiralis 4.6-9.2 (6.9) Wells, 1981 Factors affecting dynamics Willems and Meiser, 1998 Ophrys api/era 5.8-11.2 (6.6) Wells and Cox, 1991 Ophrys sphegodes 1.5-2.3 (l.9) Hutchings, 1987b Orchis militaris 2.2-7.8 (4.8) Waite and Farrell, 1998 Spiranthes spiralis 4.6-9.2 (6.9) Wells, 1981 Factors affecting dynamics…”