Species: Hieracium pilosella

Hieracium pilosella grows in dense mats, excluding other vegetation. Its major mode of reproduction is asexual but is tightly linked to flowering, as only plants which initiate inflorescences produce stolons and daughter plants (Bishop et al. 1978). After daughter plants have been produced, the mother plant dies. <br><br>Average plant age varied from study to study and site to site. In some populations individuals were replaced every one to two years, while others contained individuals up to 16 years old. If the soil in which mouse-ear hawkweed is growing is infertile, then a dense advancing front of plants will radiate from a bare center. On richer soils, inner gaps are filled when they occur. Grazing (by rabbits) was found to increase the length and double the number of stolons formed (Makepeace 1985a). Makepeace (1985b) found that mouse-ear hawkweed tends to establish on open sparsely-vegetated sites, and that seedlings sprouted only in years of higher-than-average spring rainfall. Seeds germinated most rapidly at 22 C. In the field, seeds germinated after moist intervals in spring and autumn. <br><br>In the rare instances a seedling survived beyond a few weeks, it reached adult size in 8 to 10 weeks. Mouse-ear hawkweed's dominance in an area once established is due in large part to its rosette growth pattern and stoloniferous reproduction, but it may also be allelopathic. Makepeace et al. (1985) found that umbelliferone, a known inhibitor of root growth, is present in mouse-ear hawkweed leaves and inhibited the growth of several species of clover. Alsike clover was the most effective com- petitor with mouse-ear hawkweed. <br><br>Watt (1981a, 1981b) has made long-term observations of mouse-ear hawkweed populations in England and over time has observed the establishment and rapid spread of an even-aged population of plants, followed by debris accumulation, surface leveling and stabilization coupled with plant senescence and subsequent plot diversification. In his study areas, a Festuca-dominated field was subsequently taken over by Hieracium pilosella, which in turn was being replaced by Thymus, although it was not clear whether Thymus was actively displacing the hawkweed or was filling in gaps left by the hawkweed's senescence.