ABSTRACT
The Dead Horse Mountains area of Big Bend National Park is one of the least explored areas in Texas. This is the first collective body of work to document the area’s vascular flora through a major new collection of vouchered specimens and a survey of existing herbarium specimens. Field work was performed between August 2003 and September 2006. The study area covered 176,800 acres (71,548 hectares; 276 mi2, 716 km2) with a 4100 ft (1250 m) range in elevation. Non-vascular specimens (bryophytes, hepatophytes, and lichens) were also collected but are not a part of the current report. A total of 1584 vascular specimens were collected during the current study, and 2212 previously collected specimens were found in various herbaria.
The total of the Dead Horse flora documented to date consists of 671 taxa at or below the species level (663 species) from 91 families and 344 genera. The current effort increased vouchered taxa by 12% and documented 55 novel species for the Dead Horse, a 10% increase over historical records. The best-represented families are the Asteraceae (12.0 % of total flora, 80 species), Poaceae (11.3 %, 75), Fabaceae (7.8 %, 52), Euphorbiaceae (5.1 %, 34), Cactaceae (5.1 %, 34), Pteridaceae (3.0 %, 20), and Boraginaceae (3.0%, 20). Seymeria falcata var. falcata was collected for the first time in the United States, in addition to seven new species records for Brewster County. One additional taxon may be undescribed or new to the United States. Twenty four non-native species have been collected in the Dead Horse; three are state-listed noxious weeds, and six are considered invasive. Eleven species endemic to Texas are found [p. iv] within the study area, and 17 species are considered rare. The Dead Horse flora differs from other southwestern floras, mainly in terms of the relative importance of monocots and the co-dominance of Asteraceae and Poaceae in the overall floristic composition of the Dead Horse. This and other factors suggest connections to several peripheral floristic areas, with influences ranging from the Mogollon Rim and the Great Plains, to South Texas and southern Mexico. Using similarity index calculations to compare regional floras should become an integral part of the future of defining floristic relationships of Trans-Pecos Texas and the Chihuahuan Desert Region.
ACKNOWLEDGMENTS
Mike Powell is offered my greatest appreciation and thanks for his vision for this project, which enabled my eventual involvement; for his generous assistance, helpful guidance, and consistent support; and for the collegial respect, companionship, and friendship we have enjoyed throughout this project. I wish to also recognize and thank Billie Turner, for providing such an enjoyable work environment, and for providing so much invaluable assistance towards this final product. It is because of botanists like these that current-day floristic work can occur with the degree of ease and facility we find possible. Botanists of the next generation will remain indebted to their publications and perhaps may never see their equal in their incredible command of regional floristics, from simple identifications to an intimate understanding of wide-ranging, field-level botanical relationships. They have also done an outstanding job at curating and maintaining the Sul Ross University herbarium; the exceptional organization made my work much easier by a significant degree.
I am thankful for the support given to me by Martin Terry, in addition to his excellent command of language and his perennial good-natured outlook on life. Joe Sirotnak has been an important friend and presence in my life, and he always reminds me of the joy to be found in field work. I appreciate James Zech’s encouragements to attain the highest standards possible in my work. Sul Ross State University should be recognized for continuing to support and house a vascular plant herbarium.
[p. vi]
Thanks go to the Sul Ross Biology faculty and staff for their support, Chris Ritzi for his help with grant writing, and the department as a whole for financial support and for loaning me an excellent camera for the duration of my project. Alfred Negley, Kirby Warnock, and the Big Bend Chapter of the Texas Native Plant Society all made scholarships possible through their donations. The Texas Academy of Science awarded me a graduate research grant, and a large grant contribution came from the Big Bend Natural History Association. The Friends of Big Bend National Park group was the original funding source for this study (National Park Service Task Agreement Number J717003001A and Cooperative Agreement Number H7170030001 with Sul Ross State University), enabling the project to be considered in the first place.
The staff of Big Bend National Park have been extremely helpful, including the Science and Resource Management division, especially Betty Alex; Don Sharlow and the trail crew; the Rio District rangers, especially Mike Ryan; Steve McAllister; and Diane Herring. Texas Parks and Wildlife granted me access and permits to collect in the Black Gap WMA portion of my study area, and the staff was helpful in assembling climate and ownership data. Thanks go to Jackie Poole for her help with rare plant information and for her and Jim and Ferne Scuddy’s efforts to track down, and make available to me, regional floristic publications. Many people have put their time and effort into this project: Fay Burton mounted the majority of specimens, Sharon Collyer backed me up in the field, Hillary Loring helped me feel like a more accomplished botanist, Mark Darrach assisted me on a very successful spring break expedition, Bill Dodson opened the door to the eastern side of the Dead Horse and shared his valuable experiences there, the Shackelfords allowed us access to their property in Brushy Canyon, and Richard [p. vii] Worthington and James Henrickson graciously provided data based on many years of their hard work for the floristic analyses. I would like to recognize that this study stands on the shoulders of the floristic workers who have come before me, whose work enables and enriches all that comes after.
Deep appreciation goes to my parents Ann and Jeff for their unhesitating and generous support and encouragement over the years and that their ultimate desire for me is to be happy in life. Thanks go to my brother Ben for living his life the way he wants to, finding his passion, and having a great time at it — a good inspiration. Lastly, I am so thankful for the dedicated field assistance, motivational companionship, and overall, unfailing support during the study period from Mark Yuhas. This study was more enjoyable and exciting to do, and the final product is significantly more robust, because of his involvement.
p. vii
TABLE OF CONTENTS
Abstract |
iii |
|
Acknowledgements |
v |
|
Chapter |
||
I. |
Introduction |
1 |
Geography and Study Area Description |
5 |
|
Climate |
12 |
|
Geology |
21 |
|
Soils |
33 |
|
Human History |
43 |
|
Disturbance Regimes |
49 |
|
Paleoenvironment |
58 |
|
General Vegetation Description |
62 |
|
Previous Work, Notable Species |
69 |
|
II. |
Methods |
73 |
Herbarium search |
73 |
|
Field Collections |
75 |
|
Identifications and Nomenclature |
77 |
|
III. |
Results |
79 |
Herbarium Search |
79 |
p. ix
Chapter |
Page |
|
Vegetation Patterns |
80 |
|
Mixed Desert Scrub |
81 |
|
Desert Arroyo |
85 |
|
Desert Canyon |
87 |
|
Rio Grande Riparian Corridor |
89 |
|
Sotol-Yucca Grassland |
91 |
|
Chaparral |
95 |
|
Field Collections |
94 |
|
IV. |
Discussion |
121 |
Herbarium Search |
121 |
|
Field Collections |
123 |
|
Floristic Analysis and Comparison: Local level |
129 |
|
Floristic Analysis and Comparison: Regional level |
138 |
|
Phytogeographic Context |
144 |
|
V. |
Literature Cited |
151 |
Appendix A: |
Annotated Species List of the Dead Horse Mountains Flora |
166 |
Appendix B: |
Potential Species of the Dead Horse Mountains |
263 |
Appendix C: |
Species Unlikely to Occur in the Dead Horse Mountains |
268 |
Vita |
270 |
p. x
Table |
Page |
|
1 |
Outline of plant communities of the Chihuahuan Desert Region |
65 |
2 |
Vegetation types of Big Bend National Park |
67 |
3 |
Percent composition of vegetation types in the BBNP portion of the study area |
68 |
4 |
Top 20 plant families and top 10 genera of the Dead Horse Mountains |
96 |
5 |
Taxonomic composition of the flora of the Dead Horse Mountains |
98 |
6 |
Summary of the Dead Horse Mountain flora by life form |
104 |
7 |
Non-native species collected in the Dead Horse Mountains |
105 |
8 |
Species endemic to Texas occurring in the Dead Horse Mountains |
107 |
9 |
Rare species collected in the Dead Horse Mountains |
109 |
10 |
Top 10 families of the Dead Horse Mountains and the Solitario |
131 |
11 |
Genera with the highest number of species occuring in Texas |
134 |
12 |
Comparison of top ten families in terms of proportion of flora, between four |
135 |
13 |
Comparison of family percentages between the southern Big Bend of Texas and the average of 50 southwestern U.S. floras |
140 |
14 |
Taxonomic summary of southwestern floristic areas |
142 |
15 |
Symbols used in association with the species entries in Appendix A |
169 |
16 |
Abundance categories used to describe species occurrences |
171 |
17 |
Acronyms for study area vegetation types |
172 |
p. xi
18 |
Herbarium acronyms |
174 |
19 |
Index to workers who have collected in the study area |
175 |
p. xii
Figure |
Page |
|
1 |
Vegetational areas of Texas |
2 |
2 |
Map of Big Bend National Park showing study area location |
6 |
3 |
Dead Horse Mountains study area locations |
8 |
4 |
The extent of the Chihuahuan Desert Region |
14 |
5 |
Average annual high and low temperatures of the Dead Horse Mountains |
15 |
6 |
High and low temperatures of weather stations of Big Bend National Park |
17 |
7 |
Average annual precipitation by month for Big Bend National Park and BlackGap Wildlife Management Area weather stations |
18 |
8 |
Average annual precipitation totals for Big Bend National Park and Black GapWildlife Management Area weather stations |
19 |
9 |
Low-lying clouds over higher Dead Horse peaks |
22 |
10 |
Historical annual precipitation levels for Big Bend National Park weatherstations and for the Black Gap Wildlife Management Area |
23 |
11 |
Yearly precipitation patterns during study period, 2003-2006 |
24 |
12 |
Geologic periods, typical life forms, and a general Big Bend geologic record |
26 |
13 |
Stratigraphic layers in Big Bend National Park |
27 |
14 |
Diagram of upthrust fault blocks |
31 |
15 |
Schematic drawing of high elevation soil units |
35 |
16 |
Schematic drawings of lower elevation soil units |
40 |
p. xiii
Figure |
Page |
|
17 |
Erosion of Tornillo soils into badlands formations |
41 |
18 |
Tobosa grassland on the western side of Ernst Basin |
42 |
19 |
Recorded fire events in the Dead Horse Mountains |
52 |
20 |
Non-native Phragmites australis growing densely along the Rio Grande |
54 |
21 |
Impacts from trespass livestock |
56 |
22 |
Schematic map of Trans-Pecos mountain ranges |
71 |
23 |
Mixed Desert Scrub vegetation type |
82 |
24 |
Potentially less-appreciated members of the Dead Horse flora |
86 |
25 |
Desert Canyon vegetation type |
88 |
26 |
Riparian Corridor vegetation type |
90 |
27 |
Sotol-Yucca Grassland vegetation type |
93 |
28 |
Chaparral vegetation type |
96 |
29 |
Study area collection locations |
102 |
30 |
Rare species of the Dead Horse Mountains |
111 |
31 |
Reconfirmed and newly collected rare species of the Dead Horse Mountains |
112 |
32 |
Unusual species of the Dead Horse Mountains |
114 |
33 |
Environment of the high saddle northwest of Sue Peaks |
117 |
34 |
Views from Stuarts Peak |
118 |
35 |
Views of Sue Peaks |
120 |
36 |
Species/effort trend after 100 years of collecting effort in the Dead Horse |
124 |
37 |
Species/effort trend for collections made 2003–2006 in the Dead Horse |
125 |
38 |
Species/effort trend after three visits to the Passionflower Canyon area |
126 |
p. xiv
Figure |
Page |
|
39 |
Species/effort trend after two visits to the Sue Peaks area |
128 |
p. xv
“Away from the railroad, the Big Bend – sometimes called the Bloody Bend – is a hardy country, that is, one in which, through lack of water, civilization finds it difficult to gain a foothold. Although abundantly supplied with waterworks, such as scarped and canyoned streamways, it possesses a minimum of water. These great arroyos are mocking travesties which suggest that nature becomes tired of making this country before turning on the water.”
Robert T. Hill, USGS geologist, 1889
(Maxwell 1985)
“The harsh physically inhospitable arid Big Bend area either attracts and fascinates or utterly repels the visitor…if [he] lingers however, he learns that the higher mountains are a treasure…”