Leave the Leaves!

Fallen leaves are not 'litter', but are food and shelter for many forms of wildlife.

This time of year, as the days shorten and leaves begin to fall, we can’t seem to help wanting to tidy up our yards and gardens by constantly mowing, blowing, and edging.  However, one of the most valuable things you can do to support pollinators and other beneficial species is to provide them with winter cover in the form of fallen leaves and dead plant material.

The Texas Alligator Lizard breeds in October or November, with females delaying egg
development during hibernation, laying their eggs in leaf litter beginning in February.

Leaves on the ground are not litter, which is unfortunately how most people see them.  Rather, they are food and shelter for many species of bees, beetles, butterflies, moths and other native creatures.  They are also habitat for beneficial snails, spiders, worms, millipedes, mites, and other small species that support the larger species such as birds and mammals that use them for food.

The larva or caterpillar of the Dusky-blue Groundstreak butterfly feeds on decaying leaves.

The vast majority of butterfly and moth species overwinter in the form of an egg, caterpillar, chrysalis, cocoon, or adult.  Some tuck themselves into a pile of leaves for protection from predators or the cold.  Others lay their eggs on fallen oak leaves, which becomes their first meal when they hatch in the spring.  Cocoons and chrysalises are often disguised with dried leaves, keeping them safe by helping to blend in and avoid predation.  Some species of lizard lay their eggs in fallen leaves, and many species of native bees and Sphinx moth larvae burrow into shallow soil for the winter, each attempting to survive the colder months covered in a protective blanket of leaves. 

The pupa (or immature inactive form between larva and adult)
of several species of Sphinx Moths, like this Virginia Creeper Sphinx,  
spend the winter a few inches under the soil, protected by a blanket of leaves. 

So how do you maintain your property while leaving the leaves?  First, if you must keep your lawn free of leaves, use a manual rake (it’s good exercise, too) and make a leaf pile in a corner of your yard or pile them up around your trees, shrubs, and perennials.  Don’t shred the leaves but keep them whole, let the leaf pile break down naturally, and leave the leaves that have already fallen in your beds and yard edges.  This free mulch provides you with valuable organic matter, builds up healthy soil, insulates tender roots, retains moisture, and helps to keep weeds at bay.   You can always decide to remove the leaves in the spring, once you wait late enough in the season so as not to destroy any overwintering species.

An adult Snowberry Clearwing Moth emerges from the leaf-covered ground in spring. 

And if the human side of things is more of a motivator for you, consider that the U.S. Environmental Agency has reported that mowers, edgers, and blowers used to remove leaves emit 27 million tons of air pollutants each year, not to mention the noise pollution that they create.  So do consider leaving the leaves this year, it’ll be less work for you and much better for the wildlife!

The Xerces Society encourages everyone to 
Leave the Leaves!

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.