Abstract
The Patagonian steppe is formed by tussock grasses and shrubs in a bare-soil matrix (50% cover), and as in other arid and semiarid systems, vegetation is arranged in patches. Although there is a good understanding of the probabilities of seedling establishment of Bromus pictus in relation to location within these patches, these probabilities account for only a portion of the spatial dynamics of the community. The objective of this paper was to assess the pattern and dynamics of Bromus pictus seed availability in this community, which represent the other portion of the recruitment equation. We first evaluated its seed bank along transects. Plant- or litter-covered areas had 85% of the sampled seeds; however, they accounted for 55% of the area. Bare-soil areas had seeds only if they were located close (≤10 cm) to a plant or litter microsite. In a second study, we analyzed the movement of seeds using pitfall traps. Traps located near plants captured seed amounts similar to those from traps located in bare-ground areas (far from plants). The contrast between the high number of seeds in transit and the low number of seeds retained by bare-ground microsites illustrates the importance of lateral secondary movement of seeds. We used this information on seed distribution and previous data about establishment probabilities to estimate the spatial pattern of recruitment. Microsites that are vegetated or close to individual plants are expected to recruit the greatest number of individuals. Vegetation patches play an important role in modifying ecological processes in arid and semiarid communities. Our results highlight the importance of seed distribution in the formation and maintenance of these patches.
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Claims 4
Claim · model-written summary
Plant or litter covered microsites contained 85% of sampled Bromus pictus seeds despite occupying 55% of the area.
Verbatim
e0“Plant- or litter-covered areas had 85% of the sampled seeds; however, they accounted for 55% of the area.”
e1“Bromus pictus seed availability”
Claim · model-written summary
Bare soil held seeds only within 10 cm of a plant or litter microsite.
- Taxon
- Bromus pictusBromus pictuse1
- Outcome
- seedse0
- Qualifier
- close (≤10 cm) to a plant or litter micrositee0
- Setting
- Bare-soil arease0
Verbatim
e0“Bare-soil areas had seeds only if they were located close (≤10 cm) to a plant or litter microsite.”
e1“Bromus pictus seed availability”
Claim · model-written summary
Seed traps near plants captured amounts similar to traps in bare ground far from plants.
- Taxon
- Bromus pictusBromus pictuse1
- Outcome
- seed amountse0
- Direction
- similare0
- Comparator
- bare-ground arease0
Verbatim
e0“Traps located near plants captured seed amounts similar to those from traps located in bare-ground areas (far from plants).”
e1“Bromus pictus seed availability”
Claim · model-written summary
Vegetated microsites or those close to plants were estimated to recruit the greatest number of individuals.
- Taxon
- Bromus pictusBromus pictuse1
- Outcome
- recruit the greatest number of individualse0
- Direction
- greateste0
- Setting
- Microsites that are vegetated or close to individual plantse0
Verbatim
e0“Microsites that are vegetated or close to individual plants are expected to recruit the greatest number of individuals.”
e1“Bromus pictus seed availability”