PLANT PARENTAL CARE - CONSPECIFIC NURSE EFFECTS IN FRASERA-SPECIOSA AND CIRSIUM-SCOPULORUM

We investigated whether seedling establishment in two alpine plants in Colorado was enhanced through maternally mediated nurse effects. To b enefit from an association with maternal debris, seeds must remain wit h the debris, resulting in reduced risks to seedlings and enhancement of establishment success. Seedlings of Frasera speciosa (Gentianaceae) and Cirsium scopulorum (Asteraceae) were disproportionately abundant under decaying adult rosettes and infructescences relative to other mi crosites equidistant from the parent. Beneath decaying infructescences of both species, soil was significantly moister, and evaporation rate s from hydrometers that mimicked young seedlings were significantly lo wer than in exposed (control) microsites. For F. speciosa, mean water potential of seedlings planted under infructescences was also signific antly higher than that of seedlings planted into exposed plots. These data suggest that drought stress is reduced for seedlings associated w ith adult debris. In two populations of F. speciosa, adult cover had s ignificant positive effects on seedling establishment in 1995. These a dvantages were mediated through enhanced survival of young seedlings, rather than emergence success. Cover enhanced seedling survival by 80% in one population and 145% in the other. In one population of C. scop ulorum, no seedlings were established from seeds planted with or witho ut debris in 1994 (an extremely dry year). However, in 1995 (a wetter year), seedlings were seven times more likely to emerge and about four times more likely to survive in association with debris than in expos ed plots. These results show that associations with adult debris enhan ce offspring establishment success in both plant species, and provide one of the first demonstrations of conspecific nursing, a form of pare ntal care, in plants.