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Abstract: We measured newly-produced seeds entering the
soil (Potential Seed Bank) to assess the timing and spatial patterning
of Phase I dispersal in the central Monte desert, Argentina. Rates
of forb- (6.13 mg m-2 d-1) and shrub-seed
input (48.9 mg m-2 d-1) were maximum in early
summer. The rate of grass-seed input, instead, was similar in early
and late summer (7 to 8 mg m-2 d-1). About
90% of forb- and shrub-seed mass entered the habitat through protected
(i.e., under canopy) areas, whereas 70% of grass-seed mass did so
through exposed areas. Adult plant location and the uneven impact
of wind on shrub, forb and grass seeds may explain such patterns.
We also compared the Potential Seed Bank with the soil seed bank
in the following spring (Realized Seed Bank). Seeds that form transient
banks in other ecosystems (e.g., shrub seeds of the genus Larrea,
or perennial grass seeds like those of Pappophorum and Trichloris)
prevailed in the Potential Seed Bank. Some annual forb seeds, instead,
appeared to form a more persistent seed bank, and prevailed in the
Realized Seed Bank (e.g., Chenopodium). Horizontal redistribution
did not affect the spatial patterning of forb and shrub seeds, but
produced a more homogeneous distribution of grass seeds in the habitat.
The impact of wind could explain the redistribution pattern of grass
seeds. Finally, we found almost 80% of total seeds in the top 2
cm of soil. The smallest grass and forb seeds (Sporobolus
and Descurainia) as well as some medium-sized and large forb
seeds (e.g., Glandularia, Sphaeralcea, Phacelia)
were able to reach deeper soil layers in the central Monte desert.
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