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Streptanthus bracteatus (Brassicaceae), a rare annual woodland forb, thrives in less cover: evidence of a vanished habitat?


One of the challenges of understanding habitat requirements of endangered species is that the remaining populations may not be in optimal habitat, requiring experimentation to determine optimal habitat and to guide management. A better knowledge of its habitat requirements is important for the conservation of Streptanthus bracteatus, a rare annual of central Texas woodlands. The habitat requirements of a rare, declining species like S. bracteatus can also provide insights into anthropogenic habitat degradation and into previous disturbance regimes. We conducted a garden experiment and a transplant experiment to determine the effect of different light environments on the growth and reproduction of S. bracteatus. Higher levels of light improved S. bracteatus performance, especially fecundity. The optimum level of combined canopy and understory cover at the height of a S. bracteatus plant (≤0.5 m above ground) was less than 50 %. The remaining populations of S. bracteatus are in sub-optimal habitat because it is not open enough. The results are consistent with the hypothesis that this species was a “fire-follower.” The results also support the hypotheses that central Texas woodlands were once more open and that fire played an ecological role in these woodlands, an example of the ecological requirements of a rare species revealing past community structure and dynamics.

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We thank Lisa O’Donnell for facilitating this project; Alan Pepper, Dana Price, and members of the Bracted Twistflower Working Group for useful discussions; Karen Alofs, Christina Andruk, Chris Best, Laurel Fox, Lisa O’Donnell, Mark Rees, and two anonymous reviewers for comments on earlier versions of the manuscript. Funding provided by Texas Parks and Wildlife Department (Section 6 award). We thank Brackenridge Field Laboratory, University of Texas at Austin, where the garden experiment was conducted, and Balcones Canyonlands Preserve, City of Austin, for providing a site for the field experiment.

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Correspondence to Norma L. Fowler.

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Fowler, N.L., Center, A. & Ramsey, E.A. Streptanthus bracteatus (Brassicaceae), a rare annual woodland forb, thrives in less cover: evidence of a vanished habitat?. Plant Ecol 213, 1511–1523 (2012).

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  • Endangered species
  • Fire
  • Light requirements
  • Habitat requirements
  • Optimal habitat
  • Streptanthus bracteatus