Neotinea ustulata Bateman, Pridgeon & Chase (formerly Orchis ustulata L.) is a tuberous, short-lived perennial herb noted for its relatively frequent dormancy and limited potential for clonal reproduction via buds and secondary rhizomes (Tali 2002; Tali et al. 2004). The plant has a 10–20-cm-long stem, 2–6 lanceolate leaves and a flower spike with flowers approximately 5 mm long (Tali et al. 2004). It generally grows in open, sunny meadows and prefers calcareous soils. It occurs in populations throughout Estonia, being most common on the west coast and western islands (Kull & Tuulik 2002).
We sampled and censused a total of 1013 individual plants in five populations, referred to as A, J, K, L and S, across Estonia from 1993 to 2005. Population A (Aljava, 58°33′22″N, 23°10′52″E, elevation 3–4 m) is a Carici montanae–Seslerietum meadow located on the seashore and has been ungrazed for the last 10 years. Population J (Jäneda, 59°15′19″N, 25°43′22″E, elevation 79 m) is a Melampyreo–Scorzoneretum grassland (once a sports field) and is now overgrown with pines and spruce. Population K (Kapi, 58°37′42″N, 23°12′26″E, elevation 18–19 m) is a drier Seslerio–Filipenduletum grassland that was once the site for lime burning, and is now covered with a young pine forest. Population L (Lõetsa, 58°38′47″N, 23°19′13″E, elevation 10–12 m) is a Seslerio–Filipenduletum pasture less than 1 km from the Baltic Sea. Population S (Sillukse, 58°36′53″N, 23°34′5″E, elevation 11–12 m) is an overgrown Seslerio–Filipenduletum grassland on a working limestone quarry. Four of these populations are located within 30 km of each other, including three on the island of Muhu (populations A, K and L) and one on the western coast of the mainland (population S). The fifth population (population J) is located inland, 150 km away from the other populations. Three populations consist of the early-flowering variety of N. ustulata (N. ustulata ssp. ustulata, populations A, K and L), while the remaining two populations consist of the late-flowering variety (N. ustulata ssp. aestivalis, populations J and S; Tali 2002).
Census recordings involved marking and mapping the location of each plant within 10 permanent 1 × 1 m plots per population in each growing season. Each plant's presence and life history state (i.e. flowering, vegetative or absent) were recorded annually. Plots were checked multiple times during each growing season as sprouting and flowering times vary. We sampled 180, 137, 282, 282 and 132 plants in populations A, J, K, L and S, respectively, and each plant consisted of no more than one sprout per year.