A sturdy branch, or even the trunk of a massive elm tree, begins with a tender green bud emerging from winter dormancy. From the bud, a pliable green shoot emerges. Given sufficient water and sunlight, assuming no animal or insect mischief, the young shoot grows rapidly. It reaches for the sun, its source of energy for creating carbohydrates used to build its woody structure, its fruits, and its flowers. If surrounded by tall neighbors that block morning or afternoon sun, the tree focuses its growth upward. If not surrounded by competing neighbors, but instead exposed to sunlight all day, the tree earnestly extends branches in all directions.
Laterally growing branches serve many purposes besides gathering sunlight for photosynthesis. They shade and crowd out possible competitors for light. They shade the soil, keeping the tree’s root zone cool and minimizing evaporation of soil moisture. The relatively moist cool zone under the tree makes a hospitable environment for fungi, bacteria, and microorganisms that decompose leaf litter and make nutrients available again for the benefit of the overarching tree canopy.
Birds roosting in a tree contribute their droppings which also eventually return to the soil and fertilize the tree. Birds devour insects that might attack the tree or spread pathogens that could infect the tree. Birds also consume fruit from the tree as their compensation for the task of distributing tree seeds in their excreta.
Cats perform an ambiguous role in this saga. They probably winnow out more than just the birds suffering imperfect health. I regret having pruned the lower branches from this young sapling in my garden. Without them, the neighborhood cats perceive this specimen as their ceremonial scratching post. Presumably, they scratch the bark to mark their territory. I worry that the combined marking activity of numerous felines might eventually strip enough bark to expose the vascular layer under the bark and cause serious damage to the tree. I presume that leaving the small lower branches on this tree might have discouraged such vigorous scratching frenzies. I pruned up the tree to allow the growth of sun-loving perennial flowering plants at its base. I failed to anticipate the conflict that I would set up.
Trees growing alone tend to hug the ground and build stout trunks. In their pliable youth, wind whips trees around, creating micro-breaks in their trunks. These tiny injuries heal and the resulting scar tissue thickens the trunk, making it more stalwart in the face of buffeting winds. Forest trees, surrounded closely by tall neighbors, enjoy protection from buffeting and desiccating winds. With such protection in numbers, they tend to grow tall and narrow. Wind not only threatens to break exposed limbs and trunks but speeds up evaporation from leaves and soil.
Trees fortunate enough to form a forest during wetter years write their own insurance policy against the eventuality of droughts. This mixed collection of juniper, mesquite, and other shrubby trees growing at the edge of a field of grass and forbs extends its sheltering limbs to the ground. In so doing, it not only diffuses shear stresses from wind but protects surrounding soil from the drying effects of over-exposure to sun and wind. These low-lying branches also capture wind-blown leaves that then become part of the tree’s protective mulch layer.
The sheltering forest canopy symbolizes a community and buffers its inhabitants from the damaging effects of too much sun or wind. Stored organic matter, in the form of fallen leaves, limbs, and other detritus in various stages of decay, creates in effect a reservoir that members of the forest community can draw upon even during times when nearby prairie or savannah zones go dry dormant, appearing mostly dead. In extreme drought situations, even forest denizens may shed leaves, limbs, or worse. However, even in death, these members of the forest community contribute to the welfare of future generations. Drought-killed vegetation harbors birds, reptiles, insects, other arthropods, and even some mammals in there hollows. As dead plants decay, they become more porous. In effect they become parts of a giant sponge. When rain eventually falls, the dead and decaying organic matter absorbs much of it for later use by the community and filters the portion that runs off. Without an abundance of absorbent detritus and mulch, rain water would quickly run off, taking with it an abundance of soil. Very little water would soak into the soil for future use by the local community.
Neither here nor there, contemporary institutional landscape design short-circuits the benefits of both forest and prairie biological communities. Shortly cropped turf suffers from scorching sun and never builds up a deep and durable root structure. The row of trees, kept pruned up and deprived of any mulch layer to protect their roots suffers stresses from wind shear, high heat, and dehydration. Deprived of natural processes by mowing crews in order to maintain a particular aesthetic appeal, both the fake prairie and the fake forest fragment require tremendous infusions of energy and water to keep them in their artificially static state.
Not just institutions but individual home keepers as well invest heroic amounts of energy and time to maintain wasteful landscape fashions. The fact that leaves and grass clippings from home landscapes no longer go to the municipal landfill provides little comfort to the ecologically aware. Tremendous quantities of fossil fuels contribute to manufacturing the bags, distributing and marketing the bags, collecting the filled bags and transporting them to the municipal compost factory, churning the compost to ensure speedy decomposition, packaging and marketing the resulting compost, and transporting it to customers’ landscapes. As the cost of fossil fuels resume their inexorable climb, this artificial cycle will eventually become untenable and circumstances will force us to abandon it.
Conventional landscape practices in the U.S. promote bankruptcy of the soil. Raking, bagging, and hauling away leaves and grass clippings produces the effect of mining organic matter out of the soil. Such impoverished soil can support only a limited variety of plants without a great deal of artificial intervention – i.e. irrigation, fertilizer, aeration, etc. Land stripped bare of vegetative cover requires many years to build up a soil layer capable of supporting a vigorous and resilient biological community. Current landscape maintenance practices in the United States continually strip away the organic material that would otherwise eventually become productive soil. We impoverish the soil around us in order to maintain traditions that no longer make sense. Sometimes, we humans forget to identify ourselves as members of biological communities. We must change the way we perceive the land and what grows on it.
Despite concerted efforts of city right-of-way maintenance crews to prevent the establishment and growth of unauthorized plants, sometimes, something beautiful makes an incursion. This “black brush acacia” (Acacia rigidula), apparently came in as a stowaway seedling in the container intended only for the Texas mountain laurel (Sophora secundiflora) surrounding its main stem. Both of these leguminous plants (which produce a bean-like fruit), set their own nitrogen and can thereby survive in poor soil that would discourage many other species. Relatively recent street redesign left precious little fertile topsoil in this traffic median on Dittmar Street. Despite vicious looking thorns 2-3 inches long, this acacia shrub produces a spectacular show of pale yellow flowers in late winter to early spring.
In Texas, spiny plants go with the territory. I advocate embracing these rugged but spiny plants, well, not literally. Their hardiness and drought-tolerance makes them perfectly appropriate in a region that desperately needs to save water while covering the land with a protective layer of greenery.
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