Summary1. The effect of the ratio of red : far red light (R : FR) on seed germination of herbaceous species from northern temperate deciduous forest has received little attention. Here for 27 such species, we investigated the relationship between seed mass and the suitability of micro-sites for germination. Germination in light and in darkness was compared after cold stratification, and for the light-requiring species, the germination response to R : FR was determined. In addition, seed bank persistence was monitored over 4 years. 2. With increasing seed mass, germination became less dependent on light and seed bank persistence decreased. Furthermore, for the light-dependent species, there was a significant negative relationship between the R : FR that resulted in 50% germination and seed mass. 3. These data suggest that small-seeded species only germinate in micro-sites with a high R : FR, which signals the absence of over-topping vegetation or leaf litter. Such micro-sites are comparatively rare, which may necessitate persistence in the soil seed bank. 4. For small-seeded species, we propose that a key benefit from restricting germination to high R : FR is a reduction in the time-frame over which the initially small seedlings remain small and hence highly vulnerable to mortality: high R : FR is likely to indicate high-light levels which would facilitate rapid seedling growth.

Aim Climate and land use are key determinants of biodiversity, with past and ongoing changes posing serious threats to global ecosystems. Unlike most other organism groups, plant species can possess dormant life‐history stages such as soil seed banks, which may help plant communities to resist or at least postpone the detrimental impact of global changes. This study investigates the potential for soil seed banks to achieve this. Location Europe. Time period 1978–2014. Major taxa studied Flowering plants. Methods Using a space‐for‐time/warming approach, we study plant species richness and composition in the herb layer and the soil seed bank in 2,796 community plots from 54 datasets in managed grasslands, forests and intermediate, successional habitats across a climate gradient. Results Soil seed banks held more species than the herb layer, being compositionally similar across habitats. Species richness was lower in forests and successional habitats compared to grasslands, with annual temperature range more important than mean annual temperature for determining richness. Climate and land‐use effects were generally less pronounced when plant community richness included seed bank species richness, while there was no clear effect of land use and climate on compositional similarity between the seed bank and the herb layer. Main conclusions High seed bank diversity and compositional similarity between the herb layer and seed bank plant communities may provide a potentially important functional buffer against the impact of ongoing environmental changes on plant communities. This capacity could, however, be threatened by climate warming. Dormant life‐history stages can therefore be important sources of diversity in changing environments, potentially underpinning already observed time‐lags in plant community responses to global change. However, as soil seed banks themselves appear, albeit less, vulnerable to the same changes, their potential to buffer change can only be temporary, and major community shifts may still be expected.

Germination over 3 years was followed in 25 soil samples of 31 x 31 x 5 cm each from primary and secondary stands in Bialowieza forest, Poland. The number of seedlings emerging and the number of species declined over the 3 years. In year 1 the mean densities of emerging seedlings for the primary and secondary stands were similar (2142 rrr 2 and 2488 rrr 2 respectively); in year 3 the difference was greater (248 vs 498 rrr 2 ) but not statistically significant. The trend reflected the greater longevity of the seed bank species characteristic of the secondary forest. Two functional groups of herb and shrub species were distinguished in the seed bank based on (a) frequency as adults in the present vegetation, and (b) relative abundance in the seed banks of primary and secondary forest. Group A species need large-scale gaps in the tree canopy; most have very small seeds (<0.15 mg mean dry mass) and are very persistent in the soil. Group B species benefit from single-treefall gaps in the tree canopy, but appear to be suited primarily to gaps in the canopy of the herb layer and in the root layer made mainly by animals; their seeds are not as small (mostly >0.15 mg) and not as persistent in the soil. Group B species made up 86% of the seedlings emerging over 3 years in soil from the primary stand, and 56% of those from the secondary stand. In the laboratory all five Group B species tested showed some inhibition of germination in darkness, but only one showed unequivocal inhibition by far-redenrichment of low irradiance light.

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1. Responses to climate change have often been found to lag behind the rate of warming that has occurred. In addition to dispersal limitation potentially restricting spread at leading range margins, the persistence of species in new and unsuitable conditions is thought to be responsible for apparent time-lags. Soil seed banks can allow plant communities to temporarily buffer unsuitable en-vironmental conditions, but their potential to slow responses to long-term climate change is largely unknown. As local forest cover can also buffer the effects of a warming climate, it is important to understand how seed banks might interact with land cover to mediate community responses to climate change.3. We first related species-level seed bank persistence and distribution-derived climatic niches for 840 plant species. We then used a database of plant community data from grasslands, forests and intermediate successional habitats from across