Factors affecting seed germination and seedling establishment of a long-lived desert shrub (Coleogyne ramosissima: Rosaceae)

Abstract

Long-lived desert shrubs exhibit infrequent, episodic recruitment from seed. In spite of this long time scale, selection on life history attributes that affect seedling recruitment should be strong. We studied factors affecting germination phenology and seedling establishment for Coleogyne ramosissima, a dominant shrub species in the ecotone between warm and cold deserts in western North America. We also examined ecotypic differentiation in establishment strategy in response to selection regimes in two contrasting habitats. We followed patterns of dormancy loss, germination, emergence, and survival in reciprocal field experiments at warm winter Mojave Desert and cold winter Colorado Plateau study sites. Seed germination took place in late winter, under winter rain conditions at the warm desert site and under snow at the cold desert site. Distinctive germination phenologies for the two seed populations at contrasting field sites followed predictions based on laboratory germination experiments. There was no seed bank carryover across years. Seedling survival at the end of three growing seasons was remarkably high (mean survival 54%). Most seedling mortality was due to sprout predation by rodents early the first spring in unprotected caches. Emergence and establishment at each site were significantly higher for seeds from the local population, supporting the idea of ecotypic differentiation in establishment strategy. Establishment success was an order of magnitude greater overall at the Colorado Plateau site, which represents the leading edge of an upward elevational shift in distribution for this species under the current climatic regime. The Mojave Desert site is on the trailing edge of this shift, and recruitment there is apparently a much less frequent occurrence.

Seed bank persistence of clonal weeds in contrasting habitats: implications for control

“…Consistent with our results, theoretical models predict that the ability to reproduce by vegetative growth in addition to reproduction by seeds will select for reduced seed dormancy and consequently a rapid decline in the soil seed bank (e.g., Venable and Brown 1988;Rees 1994Rees , 1996Forbis 2003). Alternatively, Meyer and Pendleton (2005) suggested that the presence of only a transient or short-term persistent seed bank could represent a response to long-term selection for germination immediately following a mast year, when predation risk to individual seeds is expected to be reduced.…”

A demographic approach to study effects of climate change in desert plants

“…It stands to reason that favourable precipitation conditions are then required for both events. There may be a range of impinging biotic factors, including the seedling's reliance on nurse plants [43], competition from established individuals [37] and predation on seed and seedlings [50]. High predation rates have led to the suggestion that mast fruiting may underlie episodic recruitment events in aridland perennial species [50,51].…”

“…There may be a range of impinging biotic factors, including the seedling's reliance on nurse plants [43], competition from established individuals [37] and predation on seed and seedlings [50]. High predation rates have led to the suggestion that mast fruiting may underlie episodic recruitment events in aridland perennial species [50,51]. Comprehensive investigations into rates of seed production, predation and seedling establishment as a function of both interannual and interseasonal variation in precipitation would be worthwhile.…”

A silviculture-oriented spatio-temporal model for germination in Pinus pinea L. in the Spanish Northern Plateau based on a direct seeding experiment

“…Among the few studies carried out either partially or completely through field trials, only general climate comparisons (Ordóñez et al 2004;Meyer and Pendleton 2005), particular climatic events (Ruano et al 2009) and understory composition (Keyes et al 2009) have been evaluated in relation to germination.…”