Friday, March 2, 2018

Early Signs of Spring

Great Purple Hairstreak on Elbowbush (Forestiera pubescens), one
of the earliest plants to bloom, often beginning in February.
A blooming Missouri Violet (Viola missouriensis) is a sure sign
that spring has arrived!
Two-Flower Anemone (Anemone edwardsiana) blooms from February
to April, and prefers the tall grassy banks of moist, shaded canyons.
The yellow blooms of Agarita (Mahonia trifoliolata) appear in
February and March, and eventually form edible red
berries relished by humans and wildlife alike.
In late February and early March, one can often hear flocks
of Sandhill Cranes honking overhead as they make
their way north with the warming weather.
A Juniper Hairstreak sips nectar from the blooms of
an Elbowbush, which is also a favorite plant of native bees.
Texas Redbud (Cercis canadensis L. var. texensis) has clusters
of flowers that appear in early spring before the leaves emerge.
One of the earliest butterflies to appear in spring, Henry's Elfin
utilizes the Texas Redbud as one of its host plants.
Nothing heralds the smell of spring like the heady scent of a
blooming Mexican Plum (Prunus mexicana)!  This small tree is a
must for any pollinator garden.
The Falcate Orangetip is a true springtime butterfly, on the wing
as early as March.

Sunday, February 18, 2018

Marvelous Mahonias

Agarita showing its simple trifoliate leaflets.
One of the constant debates in the botany world is whether or not the genus Mahonia should stand alone or be included in the genus Berberis.  This discussion is based on the fact that several species in both genera are able to hybridize, and when viewed as a whole, no consistent separation exists except for simple versus compound leaves.  Taxonomy debate aside, the two most marvelous Mahonias in Texas are the well-known Agarita (Mahonia trifoliata) and the lesser-known Texas Barberry (Mahonia swaseyi).

Agarita with red berries.
Also called Agarito, Algerita, Laredo Mahonia, Laredo Oregon-grape, Trifoliate Barberry, and Texas Wild Currant, Agarita is a 3 to 8 foot evergreen, thicket-forming shrub with gray-green to blue-gray simple leaves composed of 3 leaflets.  Holly-like, each lobe of the leaflets ends in a sharp spine, and the woody stems are bright yellow inside.  Small yellow flowers appear in February and March, followed by red, berry-like fruits from May to July. Agarita grows throughout most of South-Central and West Texas, and prefers hills, rocky slopes, and open woods that have well-drained but rocky, limestone soils.  Songbirds and small mammals will eat the fruits, and use the prickly plant for cover.  In West Texas Agarita is used as a larval host plant for the Chinati Sheepmoth, one of our native wild silk moths.

’Texas Barberry has a more compound leaf structure.
Texas Barberry, also known as Texas Oregon-grape, is a 3 to 5 foot evergreen shrub with 3 inch long compound leaves composed of 2 to 4 leaflet pairs and one terminal leaflet.  The leaflet edges have spiny teeth and prominent veins on their lower surface.  From February to April yellow flowers appear, producing small orange-red fruits in early summer.  In addition to its leaf arrangement, Texas Barberry differs from Agarita in terms of range.  While it occurs in the Edwards Plateau and in one location in the Texas Panhandle, it is endemic to the Hill Country region, where it grows in full sun to light shade on ridges with rocky, limestone soil.  Texas Barberry is also rare and much less common than Agarita, and its foliage turns reddish-purple in the fall.   

While both of these species of plants are often grown for their spiny evergreen foliage and yellow flowers in early spring, their fruits are edible for humans (as well as wildlife) and are rich in vitamin C, and have been used to make jellies, pies, cobblers, and wines.  While edible, the fruits are highly acidic and should not be eaten raw in large quantities.  Additionally, the wood of these species has been used as a light yellow dye for wool.  

Whether you are looking for a barrier plant, wildlife cover, early bloomer, edible fruits, or just something evergreen that requires little care, look no further than our native, marvelous Mahonias

Sunday, January 21, 2018

A Descent of Woodpeckers

Ladder-backed Woodpecker, male
Known for creeping up tree trunks and drilling into wood to nest and find food, woodpeckers are arboreal birds having a vertical posture, rounded wings, a chisel-shaped bill, short legs with strong claws, and stiff tail feathers.  These features enable them to climb, prey on insects, and feed on nuts and fruits.

A woodpecker uses its tail for support as it moves up a tree trunk.  Stiff, pointed tail feathers reinforced with longitudinal ridges also have small barbs that curve inward towards the tree, allowing the bird to use its tail as a brace.  Its feet are ‘zygodactyl’, meaning two toes facing forward and two toes facing backward, which helps support it when clinging to vertical surfaces. While all woodpecker bills are chisel-shaped, differences in curvature are based on the hardness of the species of wood it excavates as well as the hammering force it uses.  Tongues are also specialized in that they are barbed, sticky, and extremely long for the bird’s head, which reduces the amount of excavation required for foraging.

Ladder-backed Woodpecker, female
One of the most common and noticeable species of woodpecker in our area is the Ladder-backed Woodpecker (Picoides scalaris), which has a black and white barred back, spotted sides, and a face marked with black lines.  The males also sport an extensive reddish crown, while the female’s crown is black.  While it can nest in several types of trees, it most often nests in tall cactus in the western part of the state, giving it the old name of ‘cactus woodpecker.’  Ladder-backed woodpeckers feed on beetle larvae from small trees, but will also eat prickly pear cactus fruits (tunas) and forage on the ground for insects.  When gleaning for insects in trees, the larger male probes and pecks on trunks and larger limbs with his stouter bill, while the female more often concentrates on gleaning bark surfaces on higher branches and outer twigs.

Golden-fronted Woodpecker, female
The Golden-fronted Woodpecker (Melanerpes aurifrons) also has a black and white barred back, but a creamy white to pale yellow breast, a golden orange nape, and a small red cap on the male. A bird found west of the Balcones Escarpment, in flight they show white wing patches, a white rump, and a black tail, often calling as the glide from tree to tree.  They feed on insects, nuts (especially pecans), berries, acorns, and a wide variety of other food items, and only sometimes cache food in bark crevices.  

Downy Woodpecker, female
East of the Balcones Escarpment, the Downy Woodpecker (Picoides pubescens) has black upperparts checked with white on the wings, a boldly striped head, and a broad white stripe down the center of its back.  Its straight, chisel-like bill tends to look smaller than other woodpeckers its size, and the males have a small red patch at the back of the head.  In winter, Downy Woodpeckers are often members of mixed species flocks, allowing them to spend less time watching out for predators and better luck finding sources of food.  

The Red-bellied Woodpecker (Merlanerpes carolinus) has a patterned black and white barred back, barred central tail feathers, and a namesake small reddish patch or tinge on the belly that is often hard to spot.  The males have a solid red crown and nape, while the females only have a red nape.  Common in open woodlands, suburban areas, and parks, these woodpeckers are often seen hitching along branches and tree trunks, sometimes wedging large nuts into bark crevices and whacking them into manageable pieces using their pointed beaks.  

All woodpecker species use simple calls and drumming against tree trunks to communicate.  While the drumming is not a sure-fire way to identify a particular species, it can help you locate an individual bird, and maybe even a flock or descent of woodpeckers!

Saturday, December 30, 2017

Wintry Wonders

Agave in the Snow

While our winter weather is milder than most, our thoughts often turn to visions of ice and snow. From first frost to ice storms to snow storms, these frozen precipitation events are sporadic in Central Texas, but when they occur, they can also be spectacular!

How does frost, this sparkling layer that sometimes covers the landscape, form?  When the temperature of the air reaches a point where the water vapor in it can condense out into water, it is called the dew point.  The frost point is when the dew point falls below freezing, and rather than producing dew, it creates frost.  Consisting of tiny, spike-like crystal structures called ‘spicules’ that grow out from a solid surface, frost generally forms on surfaces that are colder than the surrounding air.  Even the size of the crystals can vary, depending upon the amount of time they took to grow, the relative changes in temperature, and the amount of water vapor available. 

Frost covers an Evergreen Sumac

Cold air is denser than warm air, so quite often when night skies are clear and calm, lower areas become colder due to differences in elevation.  Known as surface temperature inversion, this phenomenon forms ‘frost pockets’ or areas where frost forms first, due to cold air trapped against the ground.  On such days, there can be a 40 to 50 degree difference in air temperature between dawn and early afternoon.  Getting out early can reward you with a rare and wonderful spectacle of nature when something called ‘hoar frost’ is formed.

Hoar Frost formed on the edges of these Oak leaves

Referring to white ice crystals that are deposited on the ground or loosely attached to exposed objects such as leaves and branches, hoar frost forms on cold, clear nights when heat radiates out to the open sky faster than it can be replaced by nearby sources such as wind.  This allows objects in the landscape to cool below the frost point of the surrounding air, and well below the freezing point of water.  Hoar frost can form in low-lying cold air even when the air temperature a few feet above ground is well above freezing.  The name hoar comes from an Old English adjective meaning ‘showing signs of old age’, and refers to the frost making the vegetation look like it has grown white hair.  When hoar frost forms on objects above the surface, like branches and leaves, it has a feathery-like appearance and is specifically called air hoar.

Snow, on the other hand, is an entirely different matter.  When a cold water droplet freezes onto a pollen or dust particle high in the sky, it creates an ice crystal.  As this primary crystal falls toward the ground, more water vapor freezes on it, building new crystals that form the six characteristic arms of a snowflake.  This process of crystallization builds in a symmetrical or patterned way, because it reflects the internal order of the water molecules as they arrange themselves in pre-determined spaces to form the six-sided snowflake. 

Ice crystals highlight the leaves of a Sotol

The most significant factor that determines the basic shape of the ice crystal is the temperature at which it forms, and to a lesser degree humidity.  The intricate shape of a single arm of a snowflake is determined by these atmospheric conditions as the entire crystal falls.  As slight changes in temperature and humidity occur minutes or even seconds later, a crystal that begin to grow in one way might then change and branch off in a new direction. Since all six arms of a snowflake experience the same changes in atmospheric conditions, they all grow identically.  And since individual snowflakes encounter slightly different atmospheric conditions as they take different paths to the ground, they all tend to look unique, resembling everything from simple prisms and needles to intricately faceted plates and stellar dendrites.

On the surface, winter may seem as if nature is shutting down all around us, but take the time for a second look.  Aside from the visual beauty they provide, the frozen forms of precipitation during the season are just another part of the ongoing cycle of life and renewal for our native plants and animals.

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.