Seed size and seedling emergence: an allometric relationship and some ecological implications

Abstract

We develop a geometric model predicting that maximum seedling emergence depth should scale as the cube root of seed weight. We tested the prediction by planting seeds from 17 species ranging in weight from 0.1 to 100 mg at a variety of depths in a sand medium. The species were spread across 16 genera and 13 families, all occurring in fire-prone fynbos shrublands of South Africa. Maximum emergence depth was found to scale allometrically with seed weight with an exponent of 0.334, close to the predicted value. We used the allometry to predict recruitment response to experimentally simulated variation in fire intensity. Five species with small (<2 mg) seeds and five with large (>10 mg) seeds were planted at ≤20-mm and 40-mm depths and exposed to low and high heat treatments and a control. The allometric equation predicted that species with large seeds would be able to emerge from a depth of 40 mm but those with small seeds would not. Only 1% of 481 seedlings from small-seeded species emerged from the 40-mm planting compared with 40% of 626 seedlings from the large-seeded group. The simulated fire treatments killed seeds in shallow, but not deeper, soil layers. At simulated high fire intensities, seedling emergence was poor in small-seeded species but good in large-seeded species, with most seedlings emerging from the 40-mm planting depth. Seed size could be a useful general predictor of recruitment success under different fire intensities in this system. We suggest that allometric relationships in plants deserve wider attention as predictive tools.

Short dry spells in the wet season increase mortality of tropical pioneer seedlings

“…Although seed size effects on drought sensitivity were not detected in this study, a comparable field experiment that tracked both the emergence and the initial survival of pioneer seedlings at the same study site found lower survivorship of small-seeded species (Dalling and Hubbell 2002). We suggest that drought might contribute to such size-dependent seedling mortality in pioneer seedlings, since the maximum soil depth from which successful seedling emergence can take place is strongly correlated with seed mass (Bond et al 1999;Pearson et al 2002). Consequently, the very smallest-seeded pioneers such as M. argentea (0.063 mg) are only able to emerge through a few millimeters of soil (Pearson et al 2002), which exhibit the most severe drought conditions.…”

Seed germination at different temperatures and seedling emergence at different depths of Rhamnus spp

“…This may be related to the high respiration to photosynthesis ratio, as observed in adult plants [2], although whether this also occurs in seedlings should be tested. Moreover, it may be related to seed size because according to [39,40] larger seeds have more energy reserves than smaller ones and had the advantage of giving rise to taller seedlings that could emerge from deeper burials. In fact, R. ludovici-salvatoris seeds are smaller than those of R. alaternus in both populations (Esporles and Lloret) (5.4 ± 0.2 mg vs. 8.7 ± 0.3 mg and 7.7 ± 0.6 mg).…”

Seed size-number trade-off in Euterpe edulis in plant communities of the Atlantic Forest

“…Community composition can be influenced by this trait as a result of dispersal limitation processes, since the capacity of propagule movement in the landscape through wind or vertebrate dispersers is affected by seed size (Fenner and Thompson, 2005), and by seedling establishment limitation processes, since seed mass may determine seedling fitness under different water, light and nutrient conditions (Leishman and Westoby, 1994;Bond et al, 1999;Seiwa, 1998).…”