Post-dispersal fate of seeds in the Monte desert of Argentina: patterns ofgermination in successive wet and dry years

Marone, L Horno, ME Del Solar, RG

L. Marone et al., Post-dispersal fate of seeds in the Monte desert of Argentina: patterns ofgermination in successive wet and dry years, J ECOLOGY, 88(6), 2000, pp. 940-949

27

INGLESE

Article

Environment/Ecology

JOURNAL OF ECOLOGY

0022-0477 → ACNP

88

6

2000

940 - 949

ISI

0022-0477(200012)88:6<940:PFOSIT>2.0.ZU;2-7

1 Patterns of seed germination of grass and forb species were studied in op en Prosopis woodland of the central Monte desert (Argentina) during several years, to test the hypotheses that (i) seed germination is positively affe cted by both rainfall and protection afforded by vegetation cover (a facili tative effect), (ii) the number of surviving plants is positively influence d by rainfall but negatively affected by established vegetation (a competit ive effect), and (iii) seed loss from soil banks owing to germination is lo wer than that caused by granivorous animals. 2 Forb species germinated during restricted periods, either in early autumn or in spring. Grasses, however, germinated throughout the growing season, but because seedlings could not be identified to species level, it was impo ssible to discern whether different species germinated in particular season s, or if all grasses germinated in all seasons. Grass and forb germination were generally of similar magnitude, but grass germination increased by an order of magnitude during a summer of unusually abundant rainfall related t o an El Nino Southern Oscillation (ENSO) event. 3 Overall, the spatial distribution of neither germinating seeds nor surviv ing plants could be explained by interactions with established vegetation ( facilitation and competition effects, respectively). An alternative explana tion may be provided by the distribution of forb and grass seeds in the soi l. 4 Seed loss owing to germination was low in both dry and rainy years. For f orbs, such loss totalled < 1% of soil-seed reserves, and no forb species su ffered losses > 4%. Total grass-seed loss to germination was usually < 0.5% , and the 5% reached in 1997-98 corresponded to an interruption of a prolon ged drought by unusually abundant rainfall associated with a reduced seed b ank. 5 Grass-seed loss caused by germination was one to two orders of magnitude lower than that reported due to autumn-winter granivory in the central Mont e desert.