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Invasive species and endangered species

Endangered species: Streptanthus bracteatus

The annual wildflower Streptanthus bracteatus is endangered by land development, by recreational use of public land, by deer browsing, and by increasing canopy cover in woodland sites.

Zippin, D. Z. 1997. Herbivory and the population biology of a rare annual plant, the bracted twistflower (Streptanthus bracteatus). Ph.D. dissertation, University of Texas at Austin.

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

Fowler 2010. Final Report to TWPD and USFWS.

More about Streptanthus bracteatus


Invasive non-native species: Bothriochloa ischaemum

Bothriochloa ischaemum, King Ranch bluestem, is a perennial Eurasian grass that reduces diversity in central Texas savannas and sometimes forms near-monocultures. A field survey found it to be absent only from sites with woody plant canopy. It is more common along roads, but its distribution is unrelated to fire or grazing intensity.

Gabbard, B. L., and N. L. Fowler. 2006. Wide ecological amplitude of a diversity-reducing invasive grass. Biological Invasions 9:149-160.

In a garden experiment at Brackenridge Field Laboratory it out-competed the largest common native grass, Schizachyrium scoparium (lower image on right).

Effects of habitat fragmentation on B. ischaemum

king ranch bluestem

King Ranch bluestem experiment

Invasive native species: Juniperus ashei

false color aerial
false color aerial, showing plot

Endangered species: Physaria thamnophila (Zapata bladderpod)

The endangered Zapata bladderpod (Brassicaceae / mustard family) lives near the Rio Grande. Threats include development, habitat conversion to grassland for ranching, invasive grasses, and the border wall. With collaborators Chris Best (USFWS), Dana Price (TPWD), and Alice Hempel (TAMU-Kingsville), we found that it performs best in open shrubby vegetation. Pictures taken by C. Best.

Fowler, N. L., C. F. Best, D. M. Price, and A. L. Hempel. 2011. Ecological requirements of an endangered Tamaulipan thornscrub plant. Southwestern Naturalist 56:341-352.


bladderpod habitat

Endangered species: Lophophora williamsii  (peyote)

In collaboration with Dr. Martin Terry of Sul Ross University, several members of the Native American Church, and others, we have documented overharvesting of this cactus species in south Texas.  

Terry, M., K. Trout, B. Williams, T. Herrera, and N. Fowler. 2011. Limitations to natural production of Lophophora williamsii I. Regrowth and survivorship two years post harvest in a South Texas population. Journal of the Botanical Research Institute of Texas 5(2):661-675.

For more information about this species and this project, see the Cactus Conservation Organization website.

Invasive species: Centaurea stoebe (spotted knapweed)

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demography    community dynamics     herbivory

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