Clubmoss, precipitation, and microsite effects on emergence of graminoid and forb seedlings in the semiarid Northern Mixed Prairie of North America

Clubmoss (Selaginella densa Rydb.) provides extensive ground cover throughout the Northern Mixed Prairie of North America, but little is known about how this cryptogam affects seedling emergence relative to precipitation. Seedbed treatments including a control, Glyphosate applied to kill clubmoss, and clubmoss removal were factorially combined with ambient precipitation, precipitation reduced, and irrigation. Graminoid and forb emergence in the seedbeds and the microsites of live clubmoss, dead clubmoss, bare soil, litter, and caespitose grasses was determined. Forb emergence was greatest with clubmoss removal and irrigation. About 2.6–3.6-fold more forbs emerged from bare soil microsites, but clubmoss reduced forb emergence by 32–76%. Litter reduced forb emergence in 2 of 3 years. Graminoid emergence did not vary among seedbeds (P ≥ 0.780), but irrigating increased seedling emergence. Graminoid emergence was unaffected or improved in live clubmoss, dead clubmoss, bare soil, and litter microsites. In the semiarid Northern Mixed Prairie, above-average precipitation combined with bare soil will favor emergence of forbs. By contrast, clubmoss does not limit graminoids because seedlings emerge from a range of seedbeds and microsites provided diaspores are present and precipitation is above average. Emergence of graminoids and forbs is constrained primarily by precipitation in the semiarid Northern Mixed Prairie.

Research highlights
► In the semiarid Northern Mixed Prairie, above-average precipitation combined with bare soil favored emergence of forbs.
► Clubmoss did not limit graminoids because seedlings emerged from a range of seedbeds and microsites provided diaspores were present and precipitation was above average.
► Graminoid and forb seedlings were not uniformly distributed between the seed banks under clubmoss and bare soil on all sampling dates. About 1.7-2.4-fold more graminoid seedlings and 2-4 times more forb seedlings emerged from clubmoss than bare soil.
► Emergence of graminoids and forbs is constrained primarily by precipitation in the semi-arid, Northern Mixed Prairie.