Individual study: Establishment and spread of an introduced population of common cow-wheat Melampyrum pretense, an annual ant-dispersed hemiparasite, in forest at Glauer Berge near Berlin, northeast Germany
Heinken T. (2004) Migration of an annual myrmecochore: a four year experiment with Melampyrum pratense L. Plant Ecology, 170, 55-72
There is interest in dispersal mechanisms and establishment of temperate woodland plants, particularly due to evident differences in the ground flora between ancient and younger woodlands, the latter developing, for example, on former arable land or grassland. In northeast Germany (as elsewhere in European agricultural landscapes), isolated patches of forest are located in a generally inhospitable landscapes for seed dispersal of woodland ground flora. However, there is a lack data on the spread of especially ant-dispersed woodland herbs, such as common cow-wheat Melampyrum pretense. In this study, seed-sowing was used to examine establishment and colonization patterns of M.pratense in a secondary woodland in Germany which lacked a natural population of the species.
Study site: The common cow-wheat introduction site was a mixed secondary woodland at Glauer Berge, situated 20 km SSW from the Berlin city boundary, northeast Germany. Tree cover comprised predominantly Scots pine Pinus sylvestris and mixed oak Quercus forest.
Establishment of cow-wheat: One hundred cow-wheat plants were collected from Lehnin forest, an ancient mixed oak forest (25 km west of Glauer Berge) in September 1997 (the end of the growing season when these annual plants are naturally dying back). The plants were dried under ambient conditions for one week, after which all ripe seeds had been shed from the capsules. At each of three sites within Glauer Berge, 300 seeds were sown in a 1 × 1 m plot on 16 October 1997. Seeds were scattered evenly, and the litter and humus layer (scattered leaves plus a humus layer of 1-2 cm) was lightly raked to cover the seeds.
Population development and colonization: Germination and colonization patterns were investigated by recording the position of plants from 1998 to 2001. The sites were visited twice annually: spring (15 May-12 June) to record seedlings, and in summer (24 July-29 August) to record adult plants. To facilitate samping, a 20 × 20 m permanent grid was laid out in each site around the sown plot. A wider area of 50 m radius was checked for any individuals appearing further a field.
Seed fall: A small experiment was conducted in Lehnin forest between 9 August and 1 September 1998 to examine seed fall pattern. A seed trap (cardboard covered with self-adhesive plastic, 1.5 × 1.5 m), was set around a single, robust plant (height 15 cm, diameter 40 cm, max. 25 cm long lateral branches) within its natural habitat. As the released seeds become permanently adhered to the cardboard and thus cannot be removed by ants, this allowed an evaluation of primary dispersal distance.
Weather: During the growing period (April-September) all study years were warmer than the long-term average. In 1999 there was very low rainfall in combination with high temperatures which resulted in exceptionally dry conditions
Cow-wheat established at all three sown sites, with increases in both number and area of occupancy, up to at least 2001; numbers increased on average from 105 to 3,390, and area of occupancy from 2.07 to 109.04 m². Spread occurred in all directions, averaging 0.91 m/year; the highest migration rate was 6.48 m. The maximum distance an individual was recorded from the centre of a plot after three years was 7.63 m. Rates of spread were similar between the populations, but were significantly higher in 2001, presumably due to increasing population sizes. Colonization patterns were characterized by a rapid decrease in plant density with increasing distance from the sown plot, suggesting colonization by establishment of more or less isolated outposts of individuals and a gradual infill of the gaps in between.
Seed fall pattern: The seed rain of the single large Melampyrum indicated a maximum seed density between 4 and 18 cm from the stem base. The highest dispersal distance was 25 cm, and the lowest 3 cm. The median distance of seeds was 14.6 cm (n = 58).
These results resemble known myrmecochorous (ant) dispersal distances in temperate woodlands.
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