Reproductive Ecology of Two Common Woody Species, Juniperus sabina and Artemisia santolinifolia, in Mountain Steppes of Southern Mongolia

The present study describes the reproductive ecology of the prostrate shrub Juniperus sabina and the dwarf shrub Artemisia santolinifolia in dry mountain steppes of southern Mongolia. Whereas stands of the juniper are located at the drought limit of the genus’ distributional range, the genus Artemisia is typical of central Asian drylands. Both species produce large numbers of reproductive organs. For Juniperus sabina, however, only 2.5% of the morphologically intact seeds were found to be viable. Correspondingly, neither seedlings nor saplings were found in the field, and recruitment by reseeding happens at most rarely under the present climatic conditions. Instead, clonal growth is apparently the main mode of reproduction of the juniper. RAPDfingerprinting demonstrated that patches of J. sabina were constituted by a single genet. As mean current growth rates were between 1.8 and 6.8 cm/a, the largest patches found in the study area are estimated to have a minimum age of 769 to 2941 years. Thus, seedling establishment might have taken place under more favorable climatic conditions as they occurred e.g. 1800 yrBP, whereas in dry phases such as today survival is mainly guaranteed by clonal growth. In contrast to that, more than 90% of the achenes of Artemisia santolinifolia were found viable. Achenes are not dormant, however, increasing temperatures positively affected time needed for germination (32◦ > 20/10◦ > 8/4 ◦C). Germination is possible in both, light and darkness. The higher the osmotic stress the slower is germination and the fewer achenes remain viable. Therefore, it can be concluded that Artemisia santolinifolia seeds are well adapted to germinate under a wide variety of conditions, allowing the plant to colonize open sites rapidly and enabling it to invade further stands providing open space is available. Since both species grow in the same habitat, A. santolinifolia is a possible candidate for replacing J. sabina provided that the climatic conditions are not reversing again so that chances of sexual reproduction for juniper increase.