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

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

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

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

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

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

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

Old Growth Woodland (pre-1961 fire)

Younger Woodland (post-1961 fire)

Riparian

Bluestem Grasslands

Muhly Grassland (Savannahs)

Stipa Grasslands

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)

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

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

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. 1961 and 62 were average rain years and 63 was a drought. It wasn’t until 64 when normal rain returned to Austin.

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

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

1965 Here is th woody cover of 1965. 37.5 Hectares

1980 1980 40.2 Hectares

1996 And 1996 68.9 Hectares

2012 And 1996 82 Hectares

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 1996. Eventually I will have more years after I finish digitizing all of them.

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?

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