Tamarix Tamarix ramosissima on ramosissima on

the Colorado the Colorado RiverRiver

Should saltcedar be Should saltcedar be removed?removed?

Should Should saltcedar be saltcedar be

removed?removed?

Remove saltcedarRemove saltcedar The review of the literature suggests that The review of the literature suggests that

evapotranspiration (ET) of this saltcedar evapotranspiration (ET) of this saltcedar plant responsible for huge water loss. plant responsible for huge water loss.

Some contend that if saltcedar was Some contend that if saltcedar was removed, enough water could be removed, enough water could be salvaged to supply major cities with salvaged to supply major cities with enough water to meet municipal water enough water to meet municipal water demands. demands.

The replacement of native species by The replacement of native species by saltcedar is another issue of the Tamarix saltcedar is another issue of the Tamarix plant. plant.

Retain TamarixRetain Tamarix

Others state that ET loss is over Others state that ET loss is over exaggerated, and that the loss exaggerated, and that the loss of native plants is due to the of native plants is due to the stress caused by the dams that stress caused by the dams that have been placed on the rivers. have been placed on the rivers.

Despite decades of saltcedar Despite decades of saltcedar invasion and control attempts, invasion and control attempts, conflicting opinions remain conflicting opinions remain about how, where, or if about how, where, or if controlling saltcedar is likely controlling saltcedar is likely to provide ecological or to provide ecological or economic benefits that justify economic benefits that justify its removal .its removal .

Tamarisk possesses many classic Tamarisk possesses many classic weedy characteristics to which it weedy characteristics to which it owes its rapid spread and effective owes its rapid spread and effective displacement of native vegetation. displacement of native vegetation.

It produces tremendous numbers of It produces tremendous numbers of seeds which germinate quickly in a seeds which germinate quickly in a wide range of conditions, and the wide range of conditions, and the resulting plants can grow rapidly, up resulting plants can grow rapidly, up to 4 cm dayto 4 cm day

In the process, tamarisk plants In the process, tamarisk plants consume tremendous quantities of consume tremendous quantities of water and draw salts up to the water and draw salts up to the surface from deep in the soil. surface from deep in the soil.

These salts, secreted on the These salts, secreted on the invader's leaves, give rise to invader's leaves, give rise to increasingly saline soils not tolerated increasingly saline soils not tolerated by native riparian species, such as by native riparian species, such as Goodding willow (Salix gooddingii) Goodding willow (Salix gooddingii) and Fremont cottonwood (Populus and Fremont cottonwood (Populus fremontii) fremontii)

Tamarisk can tolerate both Tamarisk can tolerate both drought and flooding to degrees drought and flooding to degrees

that native species cannotthat native species cannot It can withstand submersion for up to 3 months, It can withstand submersion for up to 3 months,

but it can also survive prolonged desiccation and but it can also survive prolonged desiccation and is more able than native species to establish in is more able than native species to establish in areas with deep zones of permanent water areas with deep zones of permanent water availability.availability.

Fire may also be assisting the spread of tamarisk, Fire may also be assisting the spread of tamarisk, both because the invader resprouts readily from both because the invader resprouts readily from belowground parts, and because the belowground parts, and because the accumulation of its litter increases the probability accumulation of its litter increases the probability of fire and salinizes the soil when fires do occur.of fire and salinizes the soil when fires do occur.

On average, after accounting for possible returns On average, after accounting for possible returns of transpired water to the region, tamarisk stands of transpired water to the region, tamarisk stands consume 3000 to 4600 m3 ha−1 yr−1 more water consume 3000 to 4600 m3 ha−1 yr−1 more water than the native vegetation that they replace.than the native vegetation that they replace.

Tamarisk – the water Tamarisk – the water useruser It reaches deeper for groundwater It reaches deeper for groundwater

farther from waterways, and it builds up farther from waterways, and it builds up banks and islands, which it then banks and islands, which it then colonizes, through sediment capture colonizes, through sediment capture

Tamarisk invasion therefore represents Tamarisk invasion therefore represents not only a ha-per-ha replacement of less not only a ha-per-ha replacement of less thirsty vegetation by a species that thirsty vegetation by a species that consumes more water; it also increases consumes more water; it also increases the extent of heavily vegetated (and the extent of heavily vegetated (and therefore heavily transpiring) areas near therefore heavily transpiring) areas near waterways. waterways.

A second major impact of A second major impact of tamarix on the functioning tamarix on the functioning

of riparian ecosystems of riparian ecosystems concerns flood control. concerns flood control.

When tamarix invades a When tamarix invades a riparian corridor, it riparian corridor, it establishes in dense and establishes in dense and extensively rooted thickets. extensively rooted thickets.

These qualities—the same These qualities—the same ones that make it a valuable ones that make it a valuable tool for erosion control—tool for erosion control—also cause tamarisk to also cause tamarisk to stabilize and trap sediment stabilize and trap sediment on sandbars, riverbanks, on sandbars, riverbanks, and midstream islands and midstream islands

Steady accretion enlarges Steady accretion enlarges banks and islands, banks and islands, narrowing river channels narrowing river channels and reducing their and reducing their waterholding capacity. waterholding capacity.

southern California's Metropolitan Water southern California's Metropolitan Water District (including Los Angeles) District (including Los Angeles)

the four major cities of central Arizona the four major cities of central Arizona (Phoenix, Tucson, Scottsdale, and Mesa) (Phoenix, Tucson, Scottsdale, and Mesa)

In each case, additional water generated by In each case, additional water generated by replacing tamarix with native vegetation replacing tamarix with native vegetation would help to meet municipal water would help to meet municipal water demands.demands.

Two urban areas in the region Two urban areas in the region affected by tamarisk are actively affected by tamarisk are actively pursuing, at significant cost, pursuing, at significant cost, schemes to augment their water schemes to augment their water supplies:supplies:

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In considering the spread of saltcedar In considering the spread of saltcedar on western U.S. rivers, it is important on western U.S. rivers, it is important to distinguish between inherent to distinguish between inherent competitive advantages that saltcedar competitive advantages that saltcedar may have over native trees, that allow may have over native trees, that allow it to displace native trees, it to displace native trees,

as opposed to greater stress tolerance as opposed to greater stress tolerance that allows it to replace native trees that allows it to replace native trees when a habitat has been altered to when a habitat has been altered to the point that it no longer meets the the point that it no longer meets the niche requirements of the native niche requirements of the native trees.trees.

Competitor to native trees Competitor to native trees or or

greater stress tolerancegreater stress tolerance If saltcedar is primarily a competitor to If saltcedar is primarily a competitor to

native trees, then restoring riparian native trees, then restoring riparian habitats must involve saltcedar removal. habitats must involve saltcedar removal.

On the other hand, if saltcedar is On the other hand, if saltcedar is primarily a stress tolerant replacement primarily a stress tolerant replacement species, restoration programs that species, restoration programs that concentrate on restoring pulse flows concentrate on restoring pulse flows might be successful without the need might be successful without the need for saltcedar control. for saltcedar control.

Three primary strategies for Three primary strategies for plant growthplant growth

the degree of competition - defined as “the the degree of competition - defined as “the tendency of neighboring plants to utilize the tendency of neighboring plants to utilize the same quantum of light, ion of a mineral same quantum of light, ion of a mineral nutrient, molecule of water, or volume of nutrient, molecule of water, or volume of space” space”

Disturbance is the periodic removal of all or Disturbance is the periodic removal of all or part of a plant's biomass from the activities of part of a plant's biomass from the activities of herbivores, man, plant pathogens or natural herbivores, man, plant pathogens or natural forces such as flooding, erosion and fire.forces such as flooding, erosion and fire.

and stress in the environment consists of and stress in the environment consists of conditions that restrict a plant's primary conditions that restrict a plant's primary production, such as shortages of water, light production, such as shortages of water, light or nutrients, or the presence of excess salts. or nutrients, or the presence of excess salts.

Under a natural flood regime, Under a natural flood regime, western riparian zones can be western riparian zones can be

considered low-stress, moderate considered low-stress, moderate disturbance environmentsdisturbance environments

Perennial streams have surface flow as well as a high Perennial streams have surface flow as well as a high water table within reach of plant roots, hence there is water table within reach of plant roots, hence there is much less water stress than in the surrounding desert much less water stress than in the surrounding desert habitats habitats

Nutrient levels tend to be high compared to the Nutrient levels tend to be high compared to the surrounding desert due to the accumulation of litter surrounding desert due to the accumulation of litter

On the other hand, occasional large flood events On the other hand, occasional large flood events (return time of 5–10 years) scour the floodplain and (return time of 5–10 years) scour the floodplain and rework the alluvium, removing existing plants and rework the alluvium, removing existing plants and creating space for the establishment of new cohorts. creating space for the establishment of new cohorts.

Cottonwood and willow have been considered to be Cottonwood and willow have been considered to be ruderal, pioneer tree species in the riparian zone, able ruderal, pioneer tree species in the riparian zone, able to establish quickly and form a dominant overstory to establish quickly and form a dominant overstory following flood events following flood events

Under a regulated flow Under a regulated flow regime, riparian zones have regime, riparian zones have

tended to become high tended to become high stress, low disturbance stress, low disturbance

environmentsenvironments Banksides have become saline due to lack of Banksides have become saline due to lack of overbank flooding to leach salts from the soil,overbank flooding to leach salts from the soil,

and water tables have declined due to and water tables have declined due to withdrawal of flows to support human withdrawal of flows to support human activities. activities.

It has been proposed that reestablishment of It has been proposed that reestablishment of a natural flow regime on these rivers might a natural flow regime on these rivers might permit passive restoration of native trees, permit passive restoration of native trees, without the need for aggressive saltcedar without the need for aggressive saltcedar clearing programs clearing programs

The cost to remove Tamarix The cost to remove Tamarix could be enormous.could be enormous.

The terrain is difficult to deal The terrain is difficult to deal with. One suggested method with. One suggested method to remove Tamerix is to to remove Tamerix is to bulldoze the plant and its bulldoze the plant and its crown roots. crown roots.

This was one of the least This was one of the least expensive and most effective expensive and most effective methods proposed. methods proposed.

Bulldozers on the rugged Bulldozers on the rugged Colorado leave the question Colorado leave the question of how do you get the of how do you get the equipment to and from the equipment to and from the site. site.

Chemical controlChemical control Chemical control in association with Chemical control in association with

chainsawing existing saltcedar more chainsawing existing saltcedar more than triples the cost while reducing than triples the cost while reducing effectiveness dramatically. effectiveness dramatically.

Application of the herbicide also comes Application of the herbicide also comes into question as studies performed used into question as studies performed used fixed wing aircraft to apply the fixed wing aircraft to apply the chemicals. This approach is not practical chemicals. This approach is not practical in the Grand Canyon. The use of in the Grand Canyon. The use of helicopters is also difficult as well as helicopters is also difficult as well as being a less effective dispersal method. being a less effective dispersal method.

The third method of control proposed is the The third method of control proposed is the introduction of biological agents such as the introduction of biological agents such as the leaf eating beetle Diorhabda elongata. leaf eating beetle Diorhabda elongata.

This could help to control the present pest This could help to control the present pest Tamarix. Tamarix.

However, adaptations by a non native life However, adaptations by a non native life form could evolve, and this keeps this form could evolve, and this keeps this method as questionable, at best. method as questionable, at best.

The risk is too high to bring another The risk is too high to bring another unknown into the environment if these is an unknown into the environment if these is an other alternative. other alternative.

Cohabitation of Tamarix with native trees Cohabitation of Tamarix with native trees of willow and cottonwood trees could help of willow and cottonwood trees could help

to restore some native species to the to restore some native species to the banks of the Colorado Riverbanks of the Colorado River

This plan is financially reasonable no removal This plan is financially reasonable no removal expenseexpense

The establishment of regular large flood flow The establishment of regular large flood flow is recommended as part of the plan. is recommended as part of the plan.

The flooding would eliminate the high stress The flooding would eliminate the high stress environment that is currently imposed upon environment that is currently imposed upon the plant life of the Colorado. the plant life of the Colorado.

Studies have show that large volumes of Studies have show that large volumes of water scour the floodplain of sediment water scour the floodplain of sediment buildup produced by saltcedar. buildup produced by saltcedar.

These sediments move downstream and These sediments move downstream and reestablish beaches that have eroded due to reestablish beaches that have eroded due to low level waterflow. low level waterflow.

The Grand Canyon was shaped The Grand Canyon was shaped by floodsby floods

it is reasonable to speculate that flooding will help to it is reasonable to speculate that flooding will help to return the environment to some of its former self. return the environment to some of its former self.

The scouring of the river basin by the extreme water The scouring of the river basin by the extreme water flow will also help to remove any opportunistic flow will also help to remove any opportunistic plants that have taken up residence. plants that have taken up residence.

This will reduce the Colorado River banks overall This will reduce the Colorado River banks overall evapotranspiration rates from its present levels.evapotranspiration rates from its present levels.