Christine Westerman, Office Lead, SWCA Environmental Consultants, San Antonio office, is the author of this piece.
The live oak-Ashe juniper ecosystem is located in shallow limestone soils on hills and escarpments in the Edwards Plateau. This Central Texas ecosystem is characterized by savanna-like grassland with scattered individual tress or mottes dominated by the plateau live oak (Quercus fusiformis) and Ashe juniper (Juniperus ashei). Before European settlement, the ecosystem boasted fairly deep, uniform soils and provided habitat for native animals such as the nomadic bison, which grazed an area very intensely and then moved on, giving the prairie grasses time to recover. In addition, natural fires and fires set by Native Americans killed woody plants, promoting growth of native prairie grasses. The cycle of grazing and that of fire-and-recovery maintained ecosystems for thousands of years.
CHARACTERISTICS AND CONTRIBUTIONS OF LIVE OAK AND ASHE JUNIPER SPECIES
Live oaks, large evergreen shrubs to medium trees with dark bark, have leathery, elliptical leaves with a short (3/8-inch) petiole and produce small (5/8 to 1-inch long), light brown acorns. Live oaks provide cover and shelter for wildlife while their oil-rich acorns supply an important food source for numerous species including white-tailed deer, squirrels, javelina, and bobwhite quail. Indigenous people and early settlers made extensive use of oak acorns for food and oak wood for fuel and shelter. Even the endangered Whooping Cranes eat acorns during their annual migration from Canada to the Aransas Wildlife Refuge. Songbirds feed on the spiders, insects, and caterpillars that find habitat in live oak canopies.
Ashe juniper, often maligned as a “water-hogging” invasive, is actually a hardy native species known for its dense, twisted branches, peeling bark, and distinctive blue-green berries. This evergreen conifer offers nesting space and protection to a variety of songbird species, both native and migratory, along with a ready source of winter nutrition in the blue berries or “cones” produced in the fall. Notably, the endangered golden-cheeked warbler (Dendroica chrysoparia), which breeds exclusively in Central Texas, peels strips of bark from mature Ashe juniper trees for nesting material.
Like any natural ecosystem, the live oak/Ashe juniper community contains a diversity of trees, shrubs, grasses, and wildflowers. Common species in this ecosystem include Texas oak, cedar elm, and escarpment black cherry (especially along creeks), as well as understory shrubs such as Texas persimmon, evergreen sumac, Texas mountain laurel, agarita, and twist-leaf yucca. Cedar sedge commonly occurs in the areas shaded by live oaks and Ashe junipers and is often the only herbaceous species growing under them.Sunnier areas can support a variety of grasses such as little bluestem, Texas grama, curly mesquite, and seep muhly.
HEALTH OF THE ECOSYSTEM
The live oak/Ashe juniper ecosystem, still a vital component of the Edwards Plateau, faces several challenges that threaten its long-term sustainability. Ashe juniper expansion, for example, historically managed by periodic wildfires and grazing, has been enabled by modern land management practices, such as fire suppression and overgrazing. Unchecked juniper proliferation will reduce biodiversity, contribute to soil erosion, and alter hydrological cycles by inhibiting other ground cover. This leads to increased runoff and reduced groundwater recharge, although there is some research considering other perspectives on the effect of juniper on groundwater retention. Fragmentation due to urbanization, agriculture, and infrastructure development is another threat to the system, with its resulting habitat loss for the species that depend on large, unbroken tracts of this ecosystem.
CONSERVATION AND RESTORATION EFFORTS
Landowners, conservation organizations, and government agencies are working together to manage juniper populations, reintroduce fire as a management tool, and protect critical habitats from further fragmentation. Promotion of sustainable grazing practices and strategic water conservation are among steps that will allow the live oak-Ashe juniper ecosystem of the Edwards Plateau to remain a unique and ecologically significant landscape, shaped by millions of years of geological and climatic processes.
For material for children see Live oak/Ashe juniper Ecosystem