Walk Through Time on the Geology Trail

Walking around Phil Hardberger Park and the Geology Trail located within it, an interesting juxtaposition of geologic time can be noticed

By Ethan Bucholz

While the geologic events occurring here are nowhere near as powerful as what created the Himalayas or as violent as a volcanic eruption, they are integrally important for visitors trying to decode the history of this landscape. Take the time to look at your surroundings. While man’s hand on the situation is inevitably visible, this park is a close representation of the natural state of this area when it was devoid of human activity.

The main bedrock in the area is limestone, specifically that of the Buda Limestone formation, dating back to the Cretaceous Period.  On top of that limestone are more contemporary deposits.  The borrow pit demonstrates this.  What makes it all so interesting is the fact that these small clues give us an insight to the past, as well as an insight to the present.

Limestone deposits represent a time in the Earth’s history when massive outpourings of lava (such as the Deccan Traps in India and the Laramide Orogeny) created mountain-building events which helped form the Colorado Plateau and our modern Rocky Mountains.  These events may have contributed a significant source of carbon dioxide to the atmosphere and caused a global rise of the sea.  This transgression of the sea formed a massive interior seaway known as the Cretaceous interior seaway which extended from Hudson Bay, down through the Great Plains and the Rocky Mountains and across the whole of Texas.  Deposits of this transgression, like the Buda Limestone found at Phil Hardberger Park, represent a vast global change and a time of great deposition of marine sediments. 

Some of these sediments can be found on the highest peaks of the Rocky Mountains while others are in this beautiful park in San Antonio.  This limestone--while not the strongest-- has interacted over millions and millions of years with freshwater, creating the numerous caverns and cave formations that can be found throughout Texas and bordering states. When water interacts with calcite it re-works the chemistry of the rock and creates passageways that expand over time to form gorgeous caverns found worldwide.  This feature of the landscape is generally referred to as “Karst Topography.” The numerous ephemeral and intermittent stream channels that snake their way across the park are continuing to work upon the eroding limestone. 

The borrow pit is a small look into the fluvial nature of the Park today.  It was underwater during the Cretaceous Period, but in more modern times rivers and streams have dominated the landscape.  No longer are there deep oceans and shallow seas in this area to deposit old marine life, but instead new rivers and streams carve and deposit sediments of their own.  Looking at the borrow pit and the many clasts that can be seen in the walls along with the red color of the soils surrounding, one may surmise that this is a terrestrial and a fluvial system.  During times of flooding, sediments and larger pebbles have been deposited.  We know that they were deposited in a river or stream because they are so rounded.  These are not breccia fragments with jagged edges, but rather rounded pebbles giving us the hint to their origin.

Over time, these deposits have been re-deposited by larger, more kinetic and scouring floods and then cemented together by mud and fine particles when flooding is less severe. The overlook is a very good representation of this. On one side, the water is cutting deeper and deeper into the cliff face while on the other sediments are deposited mostly by slack water. The fluvial transition the park area has seen in the past few million years is evident even in the areas where there are only boulders. These limestone boulders are remainders of the bedrock after the wind and water eroded its surface.

The next time you walk on the Geology Trail in Hardberger Park, take notice of these clues left for us by nature. For it is by examining the past that we have a better view of our role in the grand scale of time.

Ask a Naturalist: About Naturalists

Why does Hardberger Park have a Park Naturalist?

By Wendy Leonard, PHP Park Naturalist

Hardberger Park is in the demographic heart of the city and is surrounded by development. This urban setting has presented many challenges to the ecological “health” of the park. Many people in the neighboring communities install landscape plants that are exotic and can escape cultivation and form self-propagating populations within the park. These plants compete with and will eventually exclude good, native plants. Also, this urban setting presents challenges for wildlife. In 2012, two black vultures, one crested caracara (Mexican eagle), a baby cotton-tail rabbit, and a cotton-tail rabbit family in the dog park were all rescued and either taken to a rehabilitation facility or relocated to a safer area. It is the Park Naturalist job to make sure that native plant communities are maintained and not compromised by exotic invasive plants and that any wildlife issues are dealt with in a timely, humane manner.

What does a Park Naturalist do?

Most park naturalists in general are tasked with developing and conducting interpretive programs for either local, state, or national parks. These programs are focused on the historical or natural features of the park. The natural areas within San Antonio have two Education Coordinators that facilitate this need, so the majority of my job consists of managing plant communities to maintain maximum species diversity. Most of this work targets non-native, invasive plants. I also monitor rare and endangered species like the bracted twistflower, the golden-cheeked warbler, and the black-capped vireo.  I conduct surveys on these species as well as on karst/cave features to satisfy U.S. Fish and Wildlife Service requirements. Finally, I help manage wildlife at the park including certain bird species and feral hogs.

Ask a Naturalist: How many birds seen in park?

How many different species of birds have you seen in PHP?

By Wendy Leonard, PHP Park Naturalist

Hardberger Park is an important stop for migratory birds. We have seen some unusual migrants in the park including the sage thrasher, golden-cheeked warbler, warbling vireo, blue-headed vireo, and one of my favorites, the blackburnian warbler. Bird sightings for the park are documented on ebirds.  So far, 70 different bird species have been documented on the Blanco Road entrance or north side of the park and 59 species have been documented on the NW Military entrance or south side of the park.

Wednesday, 21 November 2012

Fall Blooms at Phil Hardberger Park

Bordered patch butterfly

By Wendy Leonard, PHP Park Naturalist

This fall has brought a steady wave of beautiful butterflies to Hardberger Park. Everything from the brilliant zebra heliconian to the ubiquitous common mestra and the ever faithful monarch can be seen at the park.

Their arrival is greeted with a flurry of blooms timed so perfectly to provide these butterflies with a nectar source. Two types of mistflowers are a favorite for these butterflies and can be seen blooming now at the park

On the Blanco Road side of Hardberger Park, along Voelcker Lane, is a magnificent show of white flowers.  This is the thoroughwort or white mistflower (eupatorium havanense). These flowers, produced in large quantities, are very fragrant and not only attract butterflies but hummingbirds, bees, and other insects. This plant makes an attractive addition to any garden and is readily available in any native plant nursery.

Common mestra butterfly

The second mistflower on show at Hardberger Park is the pink thoroughwort or pink eupatorium (eupatorium incarnatum). This lower growing bush has smaller, fragrant leaves and flowers. It is blooming all along the west side of Water Loop Trail and in some locations on the NW Military side of the park.  Both of these mistflowers are an important nectar source for butterflies either travelling through our area or who call Hardberger Park their home. We encourage you to get on the trails this week and brush up on your butterfly identification skills!

Ask a Naturalist: Most Unusual thing seen in park

What’s the most unusual thing you’ve found in Hardberger Park?

By Wendy Leonard, PHP Park Naturalist

The most unusual thing I have found in the park was the golden-cheeked warbler in spring 2012. Unfortunately, the warbler only stayed around for a day before moving on to territory further north.  Golden-cheeked warblers are endangered song birds who nest only in central Texas. Every spring, they fly up from their wintering grounds in Central America to raise young right here in Texas. They have specific habitat requirements so their presence in the park was exciting to say the least.   

Returning to its roots: the restoration of grassland savanna

The ecological restoration of Phil Hardberger Park presents a remarkable opportunity to recreate and preserve a representative sample of our natural heritage.

It’s not only that wide open expanse of sky meeting the land and waving seas of grasses that is missing from the overgrazed former dairy farm, but also the many other organisms that co-evolved with and are dependent upon these grasslands. Fox, great-horned owls, red-tailed hawks, quail, armadillo, many butterflies and other insects, and a panoply of wildflowers are some of the organisms that will not exist within Phil Hardberger Park without substantial grasslands to support them.

Prior to European settlement, Central Texas — indeed, most of the state except deep East Texas — was dominated by prairie and grassland savanna. A little over one hundred years later this landscape is much altered. Overgrazing, overpopulation of deer, erosion and absence of periodic fire have drastically changed the vegetational patterns. The great Central Prairie of North America began in Canada; extending southward, it phased into a tree studded savanna in Texas, and reached into northern Mexico. Today it is estimated that as much as 99% of the native American grasslands have vanished.

Phil Hardberger Park is an example of this process. Chosen by Max and Minnie Voelcker for a dairy farm due to its expansive and productive grasslands, the park is now almost entirely dominated by young, second-growth shrubs and trees – mostly persimmon and juniper.

Based on extensive community input, the plan to develop Phil Hardberger Park for public enjoyment is based on three primary principles: 1) recreation, 2) environmental education and 3) ecological restoration of the land. Ecological restoration is essentially the repair of biological communities to maximize their ability to provide “natural services.” Natural services are products and processes provided by nature that sustain the health of our environment, including climate modification, flood control, pollution abatement, biological diversity, ground water recharge, carbon sequestration, creation of soil and erosion control, nutrient cycling, natural pest control, pollination, seed dispersal, maintenance of the composition of the atmosphere and countless other services.

To ensure maximal diversity of plant and animals species and overall ecological health of Phil Hardberger Park we must implement management programs. Nature preserves are not areas to be set aside and left alone. Due to previous and continuing impacts to our ecosystems, we must through management counterbalance negative effects.

Savannah restoration is one of the management goals for Phil Hardberger Park. The natural services at Phil Hardberger Park that will be improved through the restoration of savanna (replacing a portion of the scrub regrowth) include pollution abatement from stormwater runoff, ground water recharge, erosion control and creation of soil, and biological diversity.

Restoring the grasslands of Phil Hardberger Park also increases the amount of “edge.” Edge is an ecological concept signifying the zone where two communities intersect, in this case the forest community and the grassland community. The edge combines species of plants and animals from both communities. In addition there are species that prefer this transition zone. Thus the edge is richer in diversity than either of the two communities it joins.

As the grasslands of Phil Hardberger Park are restored and the edge effect increased, we will see (and are seeing) an overall increase in biotic diversity. The increased grasses and other herbaceous plants will support herbivores such as grasshoppers, field mice and cottontails. These in turn will support predators such as reptiles, hawks and foxes. This is a greatly simplified illustration. The actual changes will range from microscopic bacteria to large mammals.

The Master Plan for Phil Hardberger Park designates thirty acres of the original grasslands to be restored. A three-acre pilot project was undertaken in 2009. The area was cleared of 80% of its woody plants. Fifty-five thousand plugs of native grass and perennial wildflowers species were grown. These plants were installed in one morning on September 28, 2009, by over 500 community volunteers as part of National Public Lands Day and through partnership of the Conservancy with the City of San Antonio and Texas Public Radio. The three acres were also over-seeded with a broader mix of native grasses and wildflowers. A temporary irrigation system had been installed to help ensure against potential drought conditions. The irrigation system was used three times in October and November of 2009 and never since. The three acres was an ocean of color throughout spring of 2010 and had blooming, climax native grasses (some over five feet in height) by autumn of that year. Though less colorful, this restored savanna continued to perform well in the record drought of 2011, with almost 100 percent ground cover of native grassland species.

The restored savanna at Hardberger Park is also a living laboratory. Trinity University, St. Mary’s University, University of Texas at San Antonio and others are involved in various studies to increase our knowledge of the restoration and functioning of native grasslands and their inhabitants. Alamo Area Master Naturalists and Boy Scouts seeking their Hornaday Environmental award are assisting with the project.

Our challenge is now to take the restoration of grassland savanna within Phil Hardberger Park to the next level. We have a goal of restoring six additional acres in 2012. This will triple the current size of restored grassland and put us at one-third of our ultimate goal.