1. David R. Johnson Department of Biology St. Edward’s University
Identifying the factors controlling plant community structure at Wild Basin Wilderness Preserve
David R. Johnson Department of Biology St. Edward’s University

2. Wild Basin And Vireo Preserves
Wild Basin – 227 acres, off Loop 360
Late 70s - land purchased for conservation
Now owned and managed by St. Edward’s University and Travis County
Prime Golden-Cheeked Warbler habitat

3. Land Use History Cedar cutting industry (1800s – 1920s)
Unsuccessful cattle ranch (1920s-1970s)
Big fire in 1961
Conservation (1970s – present) …. SEU since 2009.

4. Questions What factors control plant community structure today?
How has this landscape regrown since the last major disturbance (1961)

5. 2013: Determining ecosystem structure at WB
Measured plant communities
14 Sites across Wild Basin

6. 2013: Determining ecosystem structure at WB
Collected Environmental Data:
Slope/Aspect/Elevation
Fractional Canopy
Soil Moisture
Soil Structure

7. Identifying Communities: Hierarchical Clustering
42 independent transects across 14 photopoints
Six major plant communities using a 60% cut off:
Juniper woodland
Dominated by red-oaks, Ashe-juniper, Lindheimer’s silktassel, with little understory (cedar sage/cedar sedge)
Riparian
No clear woody dominant, though Ashe juniper and lianas are common, high understory, very low litter
Old growth Woodland
Dominated by Ashe-juniper and live oak, with little understory (cedar sedge)
Savannah
Dominated by Seep Muhly with Ashe-juniper and other shrubs common
Flat Grassland
Primarily in VP: low overall cover, dominated by various forbs and grasses, a few shrubs
Open grassland –
Also in VP: High ground cover, dominated little blue-stem, and other grasses and shrubs

8. Old Growth Woodland (pre-1961 fire)

9. Younger Woodland (post-1961 fire)

10. Riparian

11. Bluestem Grasslands

12. Muhly Grassland (Savannahs)

13. Stipa Grasslands

14. NMS Ordination Four variables together (R2 = 0.92) explain Axis 1:
Fractional Canopy (R2 = 0.82) – higher values towards the right
Elevation (R2 = 0.06) – higher values towards the left
Slope (R2 = 0.03) – higher values towards the right
Total Rock (R2 = 0.01)

15. NMS Ordination Three variables together (R2 = 0.2) explain Axis 2:
Litter depth (R2 = 0.09) – higher values towards the bottom
Course Sand (R2 = 0.06) – higher values towards the left
Fine Sand (R2 = 0.05) – higher values towards the right

16. Student Research in 2014 & 2015
10 Students (LLC/TG) – Developed their own projects tangential to our understanding of plant community structure

17. So all the way back in April 1961 when Wild Basin a fire struck from a lit cigarette igniting a grass fire over the area. After a two day community effort the fire stopped just north of Bee creek. The fire spread about 400 acres reaching outside the Wild Basin boundary. It is said that the severity of fire could have been affected by a few things. It was an extremely drought period of time for Central Texas. There was strong wind that day due to a cold front. It was extremely difficult for fire fighting equipment to enter the canyons. And there was piles of brush all over the place due to mass land clearing in the 50s by the owner. Although it didn’t rain until June it did help recover some decent growth and 62 were average rain years and 63 was a drought. It wasn’t until 64 when normal rain returned to Austin.

18. Georeferencing Images
All parts line up at every areal photo
Six points
The current phtoto has spatial data the old doesn’t
This will stretch and adjuct eh picture to the new one
So it matches to where it actually is in space

19. Digitizing Cover
Using a threshold tool to tell the difference of what grey I want to decide what is cover and what isnt

20. 1965
Here is th woody cover of 1965.
37.5 Hectares

21. 1980
1980
40.2 Hectares

22. 1996
And 1996
68.9 Hectares

23. 2012
And 1996
82 Hectares

24. Results: between 1961 and 2012, woody cover went from ~40 to ~90% of the total Wild Basin area!!
These are the total for the three years through time. AS you can see it looks to be a pretty big increase from 1980 to Eventually I will have more years after I finish digitizing all of them.

25. Urban Socio-Ecological Systems
Current Active Management:
Control of Invasives
Suppression of Fire
New questions:
How does a fire-free urban greenspace function?
What is interannual variability?
What about water?

26. Goals for 2016
Looking for 1-2 students to do field work during summer I:
Resample community structure to determine interannual variability due to differences in precipitation and temperature
In depth soil moisture study