Environmental effects on germination of Carex utriculata and Carex nebrascensis relative to riparian restoration

Abstract

Seasonal riparian seedbed temperatures were measured and germination of Carex utriculata and C. nebrascensis seeds was tested in relation to chilling, perigynia removal, incubation temperature, and light to help guide propagation and direct seeding of these species for riparian restoration. Diurnal temperatures of riparian seedbeds at two sites in Strawberry Valley, Utah, USA ranged from 3.1 to 11.2° C in May to 9.5 to 24.1° C in August when water was generally available for seed germination. Pre-incubation treatments of chilling at 5° C for 7 to 150 days and perigynia removal increased germination of 2-year-old seeds of these species but were not necessary for high germination percentages (>89%) when seeds were incubated in light under a summer temperature regime (10 to 24° C). Seeds aged 0.5 and 1.5 years had lower germination percentages than 2-year-old seed but also had adequate germination percentages (>20%) for greenhouse propagation without pre-treatments when incubated in light at the summer temperature regime. After 5.5 years of storage at room temperatures, germination of C. utriculata was negligible, but that of C. nebrascensis was >35%. Seeds of both species that were overwintered in seed bags in riparian microsites had high germination percentages (>80%) when retrieved the following summer and incubated at a summer temperature regime in light. Althoug direct seeding in fall would allow natural chilling and potentially high germination percentages the following spring or summer, the risk of seed loss or excessive burial is great during high spring stream flows. A better strategy is to surface-seed wet seedbeds in early summer after peak flows have receded and temperature and light conditions are conducive to high germination percentages.