Sunday, December 3, 2017

Leafy Treasures

Rusty Blackhaw Viburnum

Fall is the time when the quiet, green palette of summer gives way to the crisp reds, vibrant oranges, and mellow yellows that paint the natural landscape.  During the growing seasons of spring and summer, our trees and shrubs use sunlight to convert water and carbon dioxide from the air into sugar.  Called photosynthesis, this process begins to wane in November in Central Texas, and the leaves on some plants begin to change color in preparation for winter’s rest.

Mexican Buckeye

Pigments are natural substances formed by the cells of leaves that provide the basis for leaf color. Most familiar is chlorophyll, which produces the color green, and is vitally important as it is required for photosynthesis.  Carotenoid, which produces the colors yellow, orange, and brown, is a common pigment in many fruits and vegetables, as are anthocyanins, which produce the color red. Both chlorophyll and carotenoid are present at the same time in leaf cells, but the chlorophyll covers the carotenoid and hence the leaves appear green in the spring and summer.  Not all trees can make anthocyanins, however, and most are produced under certain conditions and only in the fall.

Flameleaf Sumac

As the days grow shorter, the decreasing amount of sunlight eventually causes trees to stop producing chlorophyll.  When this happens, the carotenoid in a leaf can finally show through, turning the leaves into a myriad of yellows, oranges, and browns.  Red, on the other hand, is an entirely different matter.  Affected by temperature and cloud cover, red fall colors can vary greatly from year to year.  A lively showing of reds depends upon warm, sunny autumn days and cool, but not cold autumn nights.  This type of weather pattern triggers the production of anthocyanins, which the tree produces as a form of protection.  Anthocyanins allow trees to recover any sugar or nutrients left in the leaves, moving them through the leaf veins and down into the branches and trunk, and its presence generates the red color before the leaves fall off.  Rainfall during the year can also affect fall color, with too much lowering the overall color intensity, and too little delaying the arrival of color.

Bald Cypress

Fall leaf color can easily be used to help identify local tree and shrub species.  The most notable reds and oranges in our area are produced by Texas Red Oak, Flameleaf Sumac, and Rusty Blackhaw Viburnum.  Dotting the hillsides, roadsides, and upper reaches of wooded canyons, they contrast well with the surrounding greens of Ashe Junipers and Live Oaks.  Golds and yellows are represented by Eastern Cottonwood, Escarpment Black Cherry, Mexican Buckeye, Bald Cypress, and Little Walnut, whose colors transform the low-lying areas near creeks and streams.   

Little Walnut

While a tree’s trunk and branches can survive the colder winter temperatures, many leaves cannot. Made up of cells filled with water and sap, these tissues are unable to live throughout the winter, and the tree must shed them to ensure its survival.  As the days grow shorter, the veins that carry sap to the rest of the tree eventually close.  A separation layer forms at the base of each leaf stem, and when complete, the leaf falls.  Some oak trees are the exception, with this layer never fully detaching and the dead leaves remain on the tree until new spring growth pushes them off to the ground.  Once on the ground, the leaves slowly decompose with the help of earthworms, beneficial bacteria, and fungi, creating the soil necessary for the continuation of the cycle of life.  

Thursday, November 2, 2017

An Overwintering Texan

Rufous Hummingbird (male), Selasphorus rufus.

Late August into September typically marks migration season for hummingbirds, when most individuals move from their northern breeding grounds to their southern wintering grounds. Several factors affect this seasonal movement including amount of daylight, the angle of the sun relative to the bird’s location, availability (or lack of) food resources, and local weather patterns. Mature birds often start their migration earlier than juveniles, and males typically migrate a few days before females.  But the longest migration of any hummingbird species belongs to the Rufous Hummingbird (Selasphorus rufus), a species that can typically travel from as far away as Alaska to spend the winter in Mexico. 

A fairly small hummingbird with a nearly straight, slender bill, fairly short wings that don’t reach the end of the tail when the bird is perched, and a tail that tapers to a point when folded, the Rufous is like no other hummingbird in terms of color or behavior.  Males are bright orange on the back and belly with a vividly iridescent copper-red throat, while females are green above with orange-washed flanks and often a spot of orange in the throat.  They are the feistiest hummingbird with a gift for fast, darting flight and exceptional maneuverability, tirelessly chasing away other hummingbirds wherever they feed.  Males court females with elaborate flight displays, including J-shaped dives and nearly horizontal figure 8s.

Rufous Hummingbird (female)

In recent years, the Rufous has become the most common overwintering hummingbird in the southeastern United States, particularly along the Gulf Coast.  For the last several years we have kept a small hummingbird feeder on our back porch filled throughout the fall and winter, and have been regularly rewarded with an overwintering Rufous.  This species seems particularly able to handle the colder temperatures, perhaps because they go into ‘topor’ overnight, a reduced physiological state where their body temperature and metabolic rate are reduced.

While it has been proven that this species has an excellent memory for location, which may explain why they find our feeder year after year, it remains a mystery to scientists as to why these birds don’t complete their traditional fall migration to the Pacific coast of Mexico.  While providing a nectar feeder does not delay a hummingbird’s migration, scientists are investigating the theory that established shifts in climate and flower-blooming times are affecting their typical patterns.  Not only do these shifts appear to affect where these birds overwinter, but they also affect the timing of the clockwise circuit they make each year as they move northward up the Pacific coast in late winter and early spring, and travel southward along the chain of the Rocky Mountains in late summer. There is still much to learn about these migration patterns, and why these hummingbirds show up in places we don’t expect them to stay in winter.    

Regardless of reason, we feel fortunate to have our yard brightened during the colder months with this colorful visitor.  Why not keep a hummingbird feeder filled in your yard this season, and you just might find you have an overwintering Texan, too!

Sunday, October 8, 2017

Air Plants

Ball Moss

When the time of year arrives when leaves begin to fall and the landscape starts to appear a bit more barren, some things become more noticeable, even though they were present all along.  One such thing is epiphytes, or plants that grow harmlessly upon another plant (such as a tree), and derive moisture and nutrients from the air.  The word epiphyte comes from the Greek ‘epi’ meaning ‘upon’ and ‘phyton’ meaning ‘plant.’  Epiphytes differ from parasites in that they grow on other plants for physical support and do not necessarily negatively affect their host.  They are also called ‘air plants’ since they do not root in soil.  In central Texas, the most common epiphytes native to our area are Ball Moss (Tillandsia recurvata) and Spanish Moss (Tillandsia usneoides).  

Members of the Bromeliad or Pineapple family, neither of these plants are real mosses, but true plants with flowers and seeds.  Ball Moss is a scurfy herb with narrow leaves forming small, grayish ball-like clusters on the branches of deciduous trees.  In North America, it is native from Florida to southern Georgia, Texas, New Mexico, and Arizona, with a disjunct population in central Louisiana.  Slender, pale violet flowers appear on long bracts from June to August.  Ball Moss grows well in areas with low light, little airflow, and high humidity, which is why it is often found on shade trees in the South.  It photosynthesizes its own food by receiving water vapor from the air, nitrogen from bacteria, and other minerals from windblown dust.  Wind is also the main method of Ball Moss seed dispersal, and its plentiful seeds are armed with fine, straight hairs that cling well to wet or rough surfaces such as bark.

Spanish Moss

Generally growing upon larger trees such as Southern Live Oak and Bald Cypress, Spanish Moss forms a cascading mass of slender, scaly gray leaves.  These scales help the plant absorb water and nutrients, mostly from the minerals naturally leached from the foliage of its host tree.   Its specific name ‘usenoides’ means ‘resembling Usnea’, which is also known as Beard Lichen, but this plant is not a lichen either.  It grows in chain-like fashion to form hanging structures up to 20 feet in length, and bears tiny whitish-green flowers from April to June. Its primary range is the southeastern US, but is found as far north as Virginia, and it propagates both by seed and vegetatively with fragments carried by the wind to neighboring tree limbs.  Spanish Moss has been used for various purposes, including building insulation, packing material, and mattress stuffing.  It is still in use today for arts and crafts, and even in the manufacture of evaporative or swamp coolers.  These coolers contain thick pads of Spanish Moss that are pumped with water, with the cooling effect of evaporation caused by a fan that pulls air through the pad and into the building. 

Little evidence exists that Ball Moss 
harms the health of a tree.

There is a common misconception that these epiphytes are parasites, and that they harm the trees that serve as their hosts.  While trees that are heavily infested with these plants can have increased wind resistance and result in fallen limbs, there is little evidence among the botanist community that a reasonable presence of these plants have a noticeable effect on the growth or health of the tree.  In fact, the presence of these air plants serves as a benefit to many forms of wildlife by harboring small insects that provide food, supplying nesting material, and serving as shelter from the outside elements.

Thursday, October 5, 2017

Fields of Gold

Cooler temperatures and shorter days mark the onset of autumn, and the golden colors of the season begin to surround us.  Among the amber and scarlet hues making an appearance in the landscape, one cannot help but notice three of our most common fall-blooming native plants: Goldeneye (Viguiera dentata), Zexmenia (Wedelia acapulcensis var. hispida),  and Prairie Goldenrod (Solidago nemoralis).  

A member of the sunflower family, Goldeneye is a bushy, drought-tolerant, multi-branched plant that tends to grow in colonies, providing rich swaths of golden color along our roadsides and in open areas.  It has narrow leaves and numerous 1.5 inch daisy-like flowers at the tips of long, slender stalks.  Growing to 3 feet tall in full sun or up to 6 feet tall in partial shade, this plant is native not only to Texas but to Arizona and New Mexico as well.  It prefers relatively dry, partially shaded areas such as woodland edges and open prairies, and in Mexico is also known by the common name Chimalacate.  


The mid to late fall blooms of Goldeneye not only provide seasonal color, but provide for native wildlife as well.  Goldeneye is a larval food plant for both the Bordered Patch and Cassius Blue butterflies, and if spent flower stalks are left to stand through most of the winter, they will provide good seed forage for Lesser Goldfinches and other birds.  Infusions of this plant are still used today as an antibacterial treatment for baby rash.  

Often called Creeping-oxeye or Hairy Wedelia, Zexmenia is a small shrub 8 inches to 2.5 feet tall, that blooms continuously from May to November, although often most profusely once the weather has cooled.  The woody stems and rough-hairy green foliage give rise to showy, 1 inch wide butterscotch-orange flowers on long stems that extend vertically above the pointy-lobed leaves. Hardy, long-lived, long-blooming, and non-aggressive, this drought-tolerant plant appreciates full sun and dry, well-drained soils.  It is another host plant for the Bordered Patch butterfly, a nectar source for many species of butterflies, and its seeds are a favorite food of bobwhite quail.


Prairie Goldenrod, also called Gray Goldenrod or Field Goldenrod, is a slender-stemmed plant 1.5 to 2 feet tall, that blooms from June through October.  A member of the aster family, it has thin, coarsely-toothed leaves and yellow flowers that are borne on the upper side of hairy stalks, arching out and downward to create a vase-shaped flower cluster.  Individual plants bloom at various times, extending the flowering season, but they are most noticeable in fall, especially when paired with purple Gayfeather and red Autumn Sage.  An excellent addition to a wildflower meadow or a sunny garden, Prairie Goldenrod is naturally found in dry, open woods and upland prairies, and does well in full sun to part shade. A carefree plant, it can become invasive if left alone, but is also easily controlled.  

Prairie Goldenrod

Of special value to bees and butterflies for its pollen and nectar, and to several species of finches for its seeds, Prairie Goldenrod was also used by Native Americans to treat jaundice and kidney disorders, and as a wash for burns and skin ulcers.  The Navajo burned the leaves as incense, and used the seeds for food.

As you wander along roadways and pathways this fall, admire these fields of gold that delight not only our senses, but provide a bountiful harvest for our wild neighbors as well!

Saturday, September 16, 2017

It's a Sphinx, Methinks!

A White-lined Sphinx hovers while feeding at a thistle
A family of moths called the Sphingidae are more commonly known as hawk moths, hummingbird moths, and sphinx moths.  This family has over 1,450 species worldwide, and 73 of them are known to be present in Texas.  Generally speaking, these moths are named not just for their streamlined bullet-shaped bodies that have long narrow forewings and short hindwings, but also for their distinct behavior which comes in the form of swift, hovering flight.  Many species in this family hover in mid-air or swing from side to side when feeding on flowers, an ability that has evolved in only three other groups: hummingbirds, certain bats, and hoverflies.  In addition to nectaring on flowers, these moths often pollinate them at the same time.  

The leaf-feeding caterpillars or larva of these moths typically have a smooth body with a characteristic horn near their posterior end, hence the common name hornworm.  They pupate in an earthen cell or loose cocoon at or near the soil surface.  The word sphinx was first associated with the larva in 1736, when Rene Reaumur, a French scientist and entomologist, noted that they often assumed a pose reminiscent of the mysterious Egyptian Sphinx of antiquity.  They accomplish this pose by holding their anterior legs off their substrate and tucking their heads underneath when resting, which appears to form an upright praying position.  

Vine Sphinx

White-lined Sphinx
In our area, some of the more interesting sphinx moths include the Vine Sphinx (Eumorpha vitis), Tersa Sphinx (Xylophanes tersa), Waved Sphinx (Ceratomia undulosa), and Rustic Sphinx (Manduca rustica).  The Vine Sphinx appears similar to the well-known White-lined Sphinx, but is dark greenish-brown with a more complex pattern of sharp whitish streaks and bands on its forewings (instead of an even, pale tan stripe from base to tip intersecting uniform white lines) and a small pinkish patch on its hindwings (instead of a broad pink band).  The wingspan of this moth is 3.5 to 4 inches, it flies from April to May and July to October, and the larva feed on grapevines.  

Tersa Sphinx
The Tersa Sphinx is easily identified by its long pointed abdomen, brownish-tan forewings that look like woodgrain, and hindwings with jagged black and white markings.  This sleek, fighter jet-like moth has a wingspan of 2.5 to 3 inches, flies June to October, and its larva feed on catalpa and smooth false buttonweed.

Waved Sphinx
The Waved Sphinx has brownish-gray forewings with contrasting black streaks and zigzag lines and a small, kidney-shaped white spot outlined in black, while the hindwings are gray with darker gray shading.  Its wingspan is 3 to 4.5 inches, it flies from May to October, and its larva feed on ashes and oaks.  

Rustic Sphinx

The Rustic Sphinx has an abdomen with three pairs of yellow spots along the sides, and yellowish to chocolate-brown forewings with black zigzag lines. It has a wingspan of 3.5 to 6 inches, flies from July to October, and its larva feed on crossvine and trumpet vine. 

Certain species of sphinx moths have been widely used in scientific research aimed at better understanding animal flight and insect physiology.  Some have played a key role in advancing knowledge of hormones produced by nerve cells, while others have contributed to the development of small flying robots by shedding light on how these insects stay airborne while hovering.  Those are some pretty important roles for a sphinx, methinks!   

Wednesday, August 30, 2017

A Thistle Epistle

Mexican Yellow nectaring on Texas Thistle

As one of the most wrongly maligned and misunderstood group of wildflowers, native thistles have never been truly embraced, not even by wildscape gardeners or habitat restoration practitioners. While these plants play a significant role in our ecosystems, they have been a direct casualty of habitat loss, first by plow-based agriculture and followed by the continual development of roads and cities.  Further, recent invasions of non-native, exotic thistle species and the inability to discern them from the superficially similar native species, have contributed to their unjustified reputation and ongoing demise.

Texas Thistle, Cirsium texanum

Native thistles are a beautiful and important group of plants, with subtle blue-green foliage, fascinating stem and leaf architecture, and long-lasting pastel blooms that nourish many species of insects and birds.  The nectar they produce is utilized by many species of bees, wasps, butterflies, moths, flies, beetles, spiders, katydids, and hummingbirds, which demonstrates the wide diversity of animals supported by native thistle flowers.  In late summer and early fall, they are an essential nectar source for migrating Monarch butterflies. Their persistent seed heads provide the favorite food of goldfinches (both Lesser and American) and other songbirds such as the Carolina Chickadee, and the silky fluff attached to mature seeds is used to line their nests in the spring. 

Silvery bracts of the Texas Thistle

While there are many plants with spines that are erroneously called ‘thistles’, true thistles belong to the genus Cirsium. Of the 62 native species in North America, the most important species in our area are the Texas Thistle (Cirsium texanum) and the Yellow Thistle (Cirsium horridulum).  The Texas Thistle, also called Southern Thistle or Gray Woolly Twintip, is an upright, unbranched or sparingly branched plant, 2 to 6.5 feet tall, with grayish-green foliage that is spiny and woolly-white below.  Violet-pink to deep lavender-rose composite flower heads top the stems from April to August, and are surrounded by bracts that bear a silvery strip down the middle.  Texas Thistle is also the larval host plant for the Painted Lady and Mylitta Crescent butterflies.  

Yellow Thistle, Cirsium horridulum
Yellow Thistle, as perhaps foreshadowed by its scientific name, has a host of other, undeserved common names such as Horrid Thistle and Terrible Thistle.  It has a branching, densely hairy stem rising from a 2 foot wide basal rosette, 1 to 5.5 feet tall, with long grayish-green spiny leaves and several large flower heads.  Blooming May to August, these composite flower heads are up to 3 inches wide, surrounded by a whorl of spiny, hairy, leaf like bracts, and are frequently red-purple, pink, or white instead of the namesake yellow.  In the first year of growth this plant remains a low-lying rosette, and ‘bolts’ in the spring of the following year to reach its full height.  Yellow Thistle is an excellent attractant for Sphinx moths and is the larval host plant for the Little Metalmark and Painted Lady butterflies.  

Texas Thistle seed head

It’s time to bring back our native thistles, so this fall consider planting them in your wildscape. These species have evolved with our native pollinators in our natural habitats over thousands of years.  As a result, they benefit us by helping to sustain a healthy ecoweb, protecting our water quality, sequestering carbon in our soils, and adding a sublime beauty and structure to our landscapes.  And that’s our epistle to the thistle! 

Monday, July 10, 2017

Understanding the Balcones Canyonlands Preserve System

Fall Color in the Balcones Canyonlands Preserve (BCP)

While we are not professionals or employees of the Wildlands Conservation Division, we have volunteered for them for nearly 20 years.  We are Texas Master Naturalists and the authors of two natural history books (with a third in the works).  We also own a private preserve named Woody Hollow that is part of the BCP, and for 10 years have written monthly Nature Watch columns for local neighborhood newsletters.  We have served on the BCP Citizens Advisory Council (CAC) and feel it is important to attempt to set the record straight regarding many of the issues that have been reported regarding the BCP.

In the 1980s, during a conflict that started between land development and enrivonmental conservation, it was discovered that the Golden-cheeked Warbler (GCWA), a bird species that is highly adapted to a very specific and essential habitat in Central Texas, was in peril due to habitat fragmentation and urban sprawl (all GCWAs are native Texans but spend their winters in Central America).  As such, it was listed as a federal endangered species in 1990.  Recognizing that the Austin area was going to continue to grow rapidly (in fact, it has grown over 350% in the last 45 years), the city decided to take action.

In 1992 voters in the City of Austin passed Proposition 10, approving $22 million in bonds for the sole purpose of acquiring and improving lands to be set aside to protect water quality, conserve endagered species, and provide open space for passive public use.  These lands, made up of several tracts in western Travis County, now make up the Balcones Canyonlands Preserve (BCP) System, and are jointly managed and owned by the City of Austin, Travis County, Lower Colorado River Authority, The Nature Conservancy of Texas, Travis Audubon Society, and various private landowers (expressly through permanent conservation easements).  Collectively, activities on these lands are governed by the Balcones Canyonlands Conservation Plan (BCCP) and operated on a permit issued by the U.S. Fish and Wildlife Service (USF&WS).  These activities are carried out by biologists that work for the city or the county, and augmented by corps of specifically trained volunteers.  The preserve system protects 8 endangered species (2 songbirds, 6 karst invertebrates) and 27 species of concern (those becoming increasingly rare).

The endangered Golden-cheeked Warbler (GCWA)

There are several important factors to note regarding the preserve system, which is federally protected.  While this is not intended to be an all inclusive list, it addresses some of the most misunderstood issues and rumors:

The USF&WS permit has several conditions that must be met, and they include total acreage acquired, amount of edge habitat, and number of karst features protected.  Currently, while progress has been made, not all conditions have been satisfied.

While the BCCP and resulting preserve system is the first of its kind in the nation (i.e. made up of several distinct tracts managed by a group of partners), it is not the largest preserve in the U.S.

The USF&WS allows for a concept called ‘take’, a federal term for harm, habitat damage, or other impacts to a species survival.  Developers must pay a fee and donate alternate and suitable acres of habitat commensurate with the acres of habitat they intend to ‘destroy’.  A key point is that the official agreement states that setting aside the 30,000+ acres of preserve was mitigation for allowing 70% of the GCWA’s habitat (non-preserve land) to be developed.  As such, this agreement would be breached if any kind development or other use were allowed in the preserve system.

There has never been an official promise by any authority to ‘open up the preserve to the public’.  In fact, ‘passive public use’ refers to the grandfathering of BCP several tracts included in the overall system that have always allowed public use: Barton Creek Greenbelt, Bull Creek Greenbelt & District Park, Commons Ford Park, Emma Long Metro Park, Mt. Bonnell Park, St. Edwards Park, Stillhouse Hollow Preserve, and Wild Basin.  These ‘public use’ tracts comprise 30% of the overall preserve acreage.  Additionally, unlike these public tracts, there are very few (if any) trails on many of the other preserve tracts closed to the public.  Two of the best ways to see some of these tracts is to sign up for a guided hike or sign up to become a volunteer (

Some of the larger preserve tracts that were deeded over to the City of Austin carried with them the legal requirement that they would not ever be open for public use.

Studies are being performed continually on preserve lands to understand what is necessary to optimize conditions for protected species.  For example, data has implicitly shown that the GCWA requires closed canopy and a mix of mature, unfragmented oak-juniper woodland for breeding and nesting success.   Care needs to be taken regarding publicly reported studies regarding the GCWA; many have been proven to overestimate current populations due to incorrect assumptions in the models and/or study constructs.  Additionally, several factors will determine success, including but not limited to the number of acres of protected habitat, long-term viability of the GCWA population, and the genetic diversity of that population.

Fences have been erected to protect preserve boundaries due to vandalism by neighbors and encroachment on preserve property (fence cutting, tree cutting, trail creation, homeless camps, etc).  Two notable examples include the high-profile River Place trail closure, where a section of the trail was constructed on preserve property with no authorization, and a neighbor in Jester Estates who was arrested by the police after being given a cease and desist order for cutting down large sections of trees in the preserve adjacent to his property (twice!).

The city and the county have been very attentive to recent concerns about wildfires, and have implemented shaded fuel breaks on urban-wildland interfaces.  Note that increasing human use of preserves would likely increase the chance of human-caused fires and other management issues.  One such issue is the management of feral hogs.  They are of increasing concern and elimination efforts would be such more complicated if tracts were open to public use.

Oak - Juniper Woodland is essential habitat for the GCWA

The benefits of the preserve system are not one-sided.  For humans, it protects our natural heritage by offering sanctuary to a wide array of native plants and animals unable to adapt to urban and suburban development.  Keeping the vegetation healthy helps minimize erosion, moderates urban heat island effects, filters air & water pollutants, and allows rain to slowly infiltrate into the ground to recharge our aquifers.  

One final point.  There is a distinct difference between a ‘park’ and a ‘preserve’.  ‘Parks’ are set aside for people and their recreational activities, while ‘preserves’ are set aside to protect habitat for rare or endangered species as well as the quality of our air and water.  We’re pretty sure most reasonable people would think that’s a fair balance, and one that contributes significantly to the high quality of life here in Central Texas.

P.S. For those who are looking for more trails to use for mountain biking, hiking, and running, consider these excellent alternatives in the area:

Walnut Creek Metropolitan Park (Austin):

Flat Creek Crossing Ranch (Johnson City):

Rocky Hill Ranch (Smithville):

Milton Reimers Ranch Park (Dripping Springs):

Reveille Peak Ranch (Burnet):