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Spatial pattern and composition of the Florida scrub seed bank and vegetation along an anthropogenic disturbance gradient

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Abstract

Question

How does spatial pattern and composition of the seed bank and its relationship to above-ground cover vary across an anthropogenic disturbance gradient of intact Florida rosemary scrub, degraded scrub and improved pasture?

Location

Florida rosemary scrub, Lake Wales Ridge, Highlands County, FL, USA (27° 11′N, 81° 21′W).

Methods

In nine grid plots located in intact Florida rosemary scrub, degraded scrub and improved pasture, we assessed percentage vegetation cover and seed bank composition.

Results

The vegetation was dominated by long-lived perennials, while the seed bank was dominated by short-lived species. Shrubs were the dominant above-ground cover in rosemary scrub, sub-shrubs and the spike moss Selaginella arenicola in degraded scrub and non-native grasses in pastures. Scrub forbs were dominant in the seed bank of rosemary scrub, similar amounts of sedges, ruderal forbs and scrub forbs in degraded scrub, and ruderal species and sedges in pastures. Species absent from the vegetation were randomly distributed in the seed bank, while species present above-ground had an aggregated spatial distribution. In rosemary scrub, scrub forb seed banks were spatially aggregated and were positively associated with conspecific species above-ground and with litter cover. These patterns were not observed in degraded scrub, perhaps due to reduced shrub and increased bare ground.

Conclusion

Our results suggest that reduced shrub cover and increased bare ground in the degraded scrub may explain why there is less spatial aggregation of scrub forbs in the seed bank. Restoration of Florida rosemary scrub in pasture sites will require species reintroduction of appropriate scrub species; restoration of degraded scrub should emphasize increasing shrub cover to restore habitat spatial structure.

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