Ashe Juniper/Edwards Aquifer Debate
Although seemingly unrelated, the Ashe juniper tree and the Edwards aquifer located in the Texas Hill Country have a lot to do with the Golden-Cheeked Warbler. This is because Texans feel that they are being forced to choose between the Golden-Cheeked Warbler, their habitat, and a reliable water supply. The following sections will therefore focus on the complex relationship between the Golden-Cheeked Warbler, the Ashe juniper, and the Edwards aquifer.
Most ranchers abhor the Ashe juniper tree because it has devastated native grass species that rely on open canopies, abundant sunlight, and water, to survive in the Texas Hill Country. The Ashe juniper canopy is notoriously thick which is why it shades out the native grass species that grow beneath its canopy. This thick canopy is however the preferred habitat of the Golden- Cheeked Warbler, which is why the Ashe juniper is such a hotly debated topic. On one side there are the ranchers, who want the Ashe juniper gone so that native grasses can thrive for livestock consumption; on the other side there are naturalists, who want to preserve ideal Warbler habitat. The third perspective to take in consideration is the perspective of water conservationists. As it turns out, the increased prevalence of Ashe juniper trees has created adverse effects on the Edwards aquifer system.
The Ashe juniper is in fact a native Texan tree and although it was not always so in the past; today, the Ashe juniper dominates the landscape of the Texas Hill Country. Historically the Ashe juniper’s habitat was restricted to rocky slopes, hilltops, and moist canyons because these areas infrequently burned. With modern fire suppression, however, all areas of the Texas Hill Country rarely see any type of burning event. The Ashe juniper is also not a food source to any native species because of its high oil content (Duff, 2009). As a result there is no environmental factor keeping the Ashe junipers growth in check. During late winter and early spring the male Ashe juniper trees disperse clouds of pollen that can travel hundreds of miles on the wind. Because of their highly adaptive and efficient reproductive process, Ashe junipers have quickly spread to all parts of the Hill Country with no wild fires to keep them in check. Ashe junipers are also an incredibly hardy tree making it difficult to eradicate. If a mature juniper tree is cut down or uprooted, many young saplings will germinate in its place, making the eradication process a multi-year project. Many landowners do not have this kind of patience. As a result many ranchers will destroy the mature Ashe junipers, but allow the new saplings to grow up in subsequent years.
Not everyone wants to destroy the Ashe juniper, however, because it does serve one very important purpose: ideal Golden-Cheeked Warbler habitat. The Golden-Cheeked Warbler is a very picky bird when it comes to nesting, and it just so happens that the warbler loves the Ashe juniper. The Golden-Cheeked warbler loves to make its nest out of the Ashe juniper's bark because it manifests itself in long flakey strands. The warbler does not necessarily build its nest in an Ashe juniper tree, but junipers must be close by so that nesting material is readily available. The actual preferred habitat for the Golden-Cheeked Warbler is a juniper hardwood mix consisting of 70 percent juniper and 30 percent Live and Texas oak. This is because Warblers enjoy eating bugs that live in the oaks during early march, when they are actually building their nests but prefer juniper bud worms starting in May. Because males are territorial, the Warblers also need large continuous stretches of sloping forest habitat to provide the necessary 10 to 15 acres per nest. Bird naturalists are very concerned with providing the Golden-Cheeked Warbler with suitable habitat because the Texas Hill Country is the one and only place the birds will live in the spring and summer as seen in figure 2 above. From a bird naturalists’ point of view, the increased prevalence of thick juniper habitats in recent decades has been a good thing for the picky Warblers.
The third element to be added into the Juniper/Warbler argument is the Edwards aquifer. The Edwards aquifer is located in south-central Texas and services around 2 million people in The Austin and San Antonio area. San Antonio and especially Austin are growing at some of the fastest rates in the U.S. and as a result the demand for more water is also growing. The Edwards aquifer is broken down into three main zones: the contribution zone, the recharge zone, and the artesian zone as seen below.
Contribution Zone
The contribution zone of the Edwards aquifer occurs on the Edwards plateau; a roughly 5,400 square mile range of rugged hills (Eckhardt, 2014). This plateau was once covered in native prairie grasses which allowed for rain water to easily infiltrate through the soil down to the impermeable rock layer of the aquifer, and flow until it reached the permeable rock or recharge zone. It is now dominated by the native Ashe juniper. The ash juniper poses a few problems to the contribution zone because of its biological make-up. Firstly the Ashe juniper has a thick canopy which traps roughly 37 percent of the water that falls in an average rainfall (Duff, 2009). When the sun comes out after a particular rainfall, it quickly evaporates the water trapped in the canopy. Ashe junipers also allow a lot of litter to accumulate at their bases. This litter can soak up another 43 percent of the water that makes it through the junipers canopy (Duff, 2009). This means that only 20 percent of a one inch rainfall is able to percolate into the soil, but even this water does not get far. In an average rainfall event in the Texas Hill Country (one inch of rainfall); the 20 percent that reaches the soil will be soaked up by the junipers themselves. It will therefor take a multi-inch rain event for there to be any soil infiltration by rain water. It is because of the recent dominance of the Ashe juniper that the Edwards aquifer contribution zone has not been contributing very much water to the recharge zone in recent decades. Compound this to the fact that water demand on the aquifer is growing year by year, and the Edwards aquifer runs into supply issues.
Recharge Zone
The recharge zone of the Edwards aquifer is a 1,250 square mile area where highly permeable and fractured limestone allow large quantities of water to flow into the Edwards aquifer (Eckhardt, 2014). It is here that flowing surface water and groundwater make their way through the faults and end up in the aquifer. It is estimated that roughly 75-80 percent of the aquifers water comes from the lakes, rivers, and streams that disappear underground through sink holes (Eckhardt, 2014). As stated above, the amount of water flowing into the recharge zone from the contribution zone has been greatly reduced because of the junipers water blocking biology.
Artesian Zone
The artesian zone of the Edwards aquifer consists of the aquifer itself bordered on top and bottom by two impermeable layers of rock. It is bordered by the Glen Rose formation below and the Del Rio formation on the top (Eckhardt, 2014). The incredible weight of the new water flowing into the aquifer from the recharge zone actually forces the water up through faults and cracks in the Del Rio formation, which in turn creates artesian springs. These springs flow to the surface at sights like San Marcos springs, Comal springs, San Antonio springs, and San Pedro springs. Water in the artesian zone generally flows from southwest to northeast. A typical cross section of the entire aquifer system can be seen below.
Although seemingly unrelated, the Ashe juniper tree and the Edwards aquifer located in the Texas Hill Country have a lot to do with the Golden-Cheeked Warbler. This is because Texans feel that they are being forced to choose between the Golden-Cheeked Warbler, their habitat, and a reliable water supply. The following sections will therefore focus on the complex relationship between the Golden-Cheeked Warbler, the Ashe juniper, and the Edwards aquifer.
Most ranchers abhor the Ashe juniper tree because it has devastated native grass species that rely on open canopies, abundant sunlight, and water, to survive in the Texas Hill Country. The Ashe juniper canopy is notoriously thick which is why it shades out the native grass species that grow beneath its canopy. This thick canopy is however the preferred habitat of the Golden- Cheeked Warbler, which is why the Ashe juniper is such a hotly debated topic. On one side there are the ranchers, who want the Ashe juniper gone so that native grasses can thrive for livestock consumption; on the other side there are naturalists, who want to preserve ideal Warbler habitat. The third perspective to take in consideration is the perspective of water conservationists. As it turns out, the increased prevalence of Ashe juniper trees has created adverse effects on the Edwards aquifer system.
The Ashe juniper is in fact a native Texan tree and although it was not always so in the past; today, the Ashe juniper dominates the landscape of the Texas Hill Country. Historically the Ashe juniper’s habitat was restricted to rocky slopes, hilltops, and moist canyons because these areas infrequently burned. With modern fire suppression, however, all areas of the Texas Hill Country rarely see any type of burning event. The Ashe juniper is also not a food source to any native species because of its high oil content (Duff, 2009). As a result there is no environmental factor keeping the Ashe junipers growth in check. During late winter and early spring the male Ashe juniper trees disperse clouds of pollen that can travel hundreds of miles on the wind. Because of their highly adaptive and efficient reproductive process, Ashe junipers have quickly spread to all parts of the Hill Country with no wild fires to keep them in check. Ashe junipers are also an incredibly hardy tree making it difficult to eradicate. If a mature juniper tree is cut down or uprooted, many young saplings will germinate in its place, making the eradication process a multi-year project. Many landowners do not have this kind of patience. As a result many ranchers will destroy the mature Ashe junipers, but allow the new saplings to grow up in subsequent years.
Not everyone wants to destroy the Ashe juniper, however, because it does serve one very important purpose: ideal Golden-Cheeked Warbler habitat. The Golden-Cheeked Warbler is a very picky bird when it comes to nesting, and it just so happens that the warbler loves the Ashe juniper. The Golden-Cheeked warbler loves to make its nest out of the Ashe juniper's bark because it manifests itself in long flakey strands. The warbler does not necessarily build its nest in an Ashe juniper tree, but junipers must be close by so that nesting material is readily available. The actual preferred habitat for the Golden-Cheeked Warbler is a juniper hardwood mix consisting of 70 percent juniper and 30 percent Live and Texas oak. This is because Warblers enjoy eating bugs that live in the oaks during early march, when they are actually building their nests but prefer juniper bud worms starting in May. Because males are territorial, the Warblers also need large continuous stretches of sloping forest habitat to provide the necessary 10 to 15 acres per nest. Bird naturalists are very concerned with providing the Golden-Cheeked Warbler with suitable habitat because the Texas Hill Country is the one and only place the birds will live in the spring and summer as seen in figure 2 above. From a bird naturalists’ point of view, the increased prevalence of thick juniper habitats in recent decades has been a good thing for the picky Warblers.
The third element to be added into the Juniper/Warbler argument is the Edwards aquifer. The Edwards aquifer is located in south-central Texas and services around 2 million people in The Austin and San Antonio area. San Antonio and especially Austin are growing at some of the fastest rates in the U.S. and as a result the demand for more water is also growing. The Edwards aquifer is broken down into three main zones: the contribution zone, the recharge zone, and the artesian zone as seen below.
Contribution Zone
The contribution zone of the Edwards aquifer occurs on the Edwards plateau; a roughly 5,400 square mile range of rugged hills (Eckhardt, 2014). This plateau was once covered in native prairie grasses which allowed for rain water to easily infiltrate through the soil down to the impermeable rock layer of the aquifer, and flow until it reached the permeable rock or recharge zone. It is now dominated by the native Ashe juniper. The ash juniper poses a few problems to the contribution zone because of its biological make-up. Firstly the Ashe juniper has a thick canopy which traps roughly 37 percent of the water that falls in an average rainfall (Duff, 2009). When the sun comes out after a particular rainfall, it quickly evaporates the water trapped in the canopy. Ashe junipers also allow a lot of litter to accumulate at their bases. This litter can soak up another 43 percent of the water that makes it through the junipers canopy (Duff, 2009). This means that only 20 percent of a one inch rainfall is able to percolate into the soil, but even this water does not get far. In an average rainfall event in the Texas Hill Country (one inch of rainfall); the 20 percent that reaches the soil will be soaked up by the junipers themselves. It will therefor take a multi-inch rain event for there to be any soil infiltration by rain water. It is because of the recent dominance of the Ashe juniper that the Edwards aquifer contribution zone has not been contributing very much water to the recharge zone in recent decades. Compound this to the fact that water demand on the aquifer is growing year by year, and the Edwards aquifer runs into supply issues.
Recharge Zone
The recharge zone of the Edwards aquifer is a 1,250 square mile area where highly permeable and fractured limestone allow large quantities of water to flow into the Edwards aquifer (Eckhardt, 2014). It is here that flowing surface water and groundwater make their way through the faults and end up in the aquifer. It is estimated that roughly 75-80 percent of the aquifers water comes from the lakes, rivers, and streams that disappear underground through sink holes (Eckhardt, 2014). As stated above, the amount of water flowing into the recharge zone from the contribution zone has been greatly reduced because of the junipers water blocking biology.
Artesian Zone
The artesian zone of the Edwards aquifer consists of the aquifer itself bordered on top and bottom by two impermeable layers of rock. It is bordered by the Glen Rose formation below and the Del Rio formation on the top (Eckhardt, 2014). The incredible weight of the new water flowing into the aquifer from the recharge zone actually forces the water up through faults and cracks in the Del Rio formation, which in turn creates artesian springs. These springs flow to the surface at sights like San Marcos springs, Comal springs, San Antonio springs, and San Pedro springs. Water in the artesian zone generally flows from southwest to northeast. A typical cross section of the entire aquifer system can be seen below.