Tamarisk has a natural tendency to grow into very dense thickets, at times as many as 3000 plants per acre, which prevent the expansion of native vegetation (1). Native to Central Asia and the Mediterranean, this plant species has an “extensive root system well suited to the hot, arid climates and alkaline soils common in the western United States” (1). This specific species of plant mines into the watershed, monopolizing the water supply, and enabling tamarisk to thrive while native vegetation perishes.  Due to the depth of its far-reaching root system, tamarisks draw more salts from the groundwater than native vegetation which is then excreted through the leaves and deposited into the soil once they fall off the plant. This process causes an increase in soil salinity which in turn prevents the germination of many native plants, allowing tamarisk to take over. “Because tamarisk stands develop into dense thickets, sediment accumulates in their extensive root systems and promotes further tamarisk growth, “ (1, p.1).  From the rafts, we observed that tamarisk dominated the shoreline with no other flora competing for even the smallest space.  

In addition to out-competing other native plant species, the spread of tamarisk causes other problems as well.  The dense habitat of the plant limits recreational access to the river.  The dense growth also causes a fire hazard and allows fires to spread where once they weren’t such an influence on the ecosystem. Another impact is due to their accumulation of soil, tamarisks cause river and stream channels to gradual narrow and flooding increases (1, p.1).  Yet still another negative consequence is, “conversion to tamarisk typically coincides with reduction or complete loss of bird species strongly associated with cottonwood-willow habitats http://bulk.resource.org/gpo.gov/register/1995/1995_10708.pdf. If ecological reasons aren’t bad enough, “cottonwoods and willows are culturally valuable to tribes such as the Hopi and the Navajo.  Roots, branches, and logs are used in baskets, kachinas, and structures” (http://www.gcrg.org/bqr/13-3/aliens.html).  

As I stared at the river bank, I wondered what the area looked like 50 and 100 years ago, before the takeover of tamarisk?  Bret pointed out the huge flood plain in the upper part of the river that once existed before dams upstream started controlling the water flow. Bret showed us old river channels that were still lined by the native cottonwoods.  Camping under cottonwood trees in particular is ideal as the trees cast a cool shadow from the hot, high desert sun.

For all of the above reasons, the prevailing thinking has been to eradicate tamarisks and restore once native vegetation.  Mechanical, chemical, and biological eradication efforts have all been experimented with to prevent further spreading of tamarisks.  There have been attempts to reverse the damage that has already occurred and return river corridors in the West to their original state. Mechanical removal efforts are methods by which the shrub or tree is cut or mowed, however this is rarely effective as re-growth is high. Burning is not a viable option either as tamarisk can recover far quicker from fire damage than native vegetation can because it sprouts vigorously from the root crown. (2) The abundance of leaf litter from tamarisk raises the threat of wildfires which actually stimulates its growth, but destroys native vegetation such as cottonwoods and willows.

Chemical methods involve cutting the stump of a tamarisk two inches above the soil surface and treating it with an herbicide immediately. When the bark is dry, another herbicide can be applied near the base of the plant. In the fall months, herbicides may be sprayed on the foliage, however re-growth is common following these methods and re-treatment must be applied in order to kill the shrub (2).

Biological eradication methods involve the use living organisms in order to suppress the growth of the tamarisk species. Diorhabda elongata, or the “tamarisk leaf beetle,” has been tested since 1992 and approval of field testing was granted in 1999.  In 2001, beetles were released into the wild.  This biological control is still relatively “new” and the overall effect it will have on the suppression of tamarisk growth is still being observed and studied.  Beetles control tamarisk by feeding on the plants in massive hoards, completely defoliating the plant which prevents photosynthesize and storage of food in root systems. Repetition of this process over the course of years causes the roots to diminish in size to such a degree that they can no longer support the plant. Introduction of a foreign organism, like beetles, into an ecosystem has raised concerns.  Years of testing, prior to being released into the wild, has shown that the beetles prefer the species of tamarisk over other native flora (2).

Not all scientists saccept that tamarisks need to be removed everywhere in the West. Biologists studying the endangered willow flycatchers discovered a significant amount of the remaining 400 pairs of birds now nest in tamarisks- indicating how long the plants have been around (3)  “The attraction is proximity to water, shade and a branching structure that apparently reminds the birds of the native willow trees they historically nested in.”  So, if enough beetles were released to eat, “… all of the tamarisk, the reasoning went, an important chunk of nesting habitat would disappear, pushing the bird closer to extinction.”  This argument is found in a fascinating article entitled, “Tackling tamarisk” a feature story- from the May 25, 1998 issue of High Country News by Paul Larmer.  Larmer interviewed an ecologist, Bob Ohmard, of Arizona State University,  who did “pioneering studies in the 1970s showing that tamarisk supports less animal life – from insects to birds and mammals – than native vegetation.  …Ohmart argues that tamarisk has merely taken advantage of our sick, static river systems, and that removal of it will leave next to no habitat for the willow flycatcher and other riparian-dependent species.  Dams and water diversions have permanently altered river corridors in the West, he says, rendering many inhospitable to native cottonwoods and willows.  ‘If you wipe out saltcedar, what will replace it? Not much,’ says Ohmart. ‘I’d rather see a monoculture of saltcedar than bare dirt. At least it holds in soil and provides a little habitat. We’re damn lucky tamarisk came along when it did.’  

Backing up Ohmart is Bertin Anderson, an ornithologist turned soil scientist based in Blythe, Calif.. “Removing tamarisk and replacing it with native vegetation isn’t going to happen on any major river in the Southwest,” says Anderson, who has spent the last 25 years restoring native vegetation to sites along the lower Colorado River for the Bureau of Reclamation, various Indian tribes and other clients.  Rivers and their banks have become saltier and drier since irrigated agriculture and dams came in more than 50 years ago, he says, and these conditions favor the hardier salt cedar over the cottonwoods and willows. Anderson says that dams have prevented the nurturing floods that wash salts out of the soil and moisten it to sustain native plants. “  Anderson says he analyzed a large portion of the Southwest’s rivers, looking at soil conditions, and found that 75 percent of the area is no longer suitable for natives.  ‘But a large percentage of the area is still suitable for tamarisk,’ he says. ‘In some places, the conditions are so bad that even tamarisk can’t survive.’  Ohmart’s and Anderson’s viewpoints have elicited visceral reactions from those involved with tamarisk control.  “I don’t want to damage the willow flycatcher, but it’s clear that the willow flycatcher has been hurt by saltcedar,” says DeLoach. “There are 50 other endangered riparian species that could benefit from biocontrol of saltcedar. The Fish and Wildlife Service needs to look at the benefits to the whole ecosystem, not just the willow flycatcher. You want to manage for flux.”  

It seemed like our PSU group was in such a rural, unpopulated area of Utah, and yet once we were told about the invasive tamarisks, the impact of humans became clearly visible. A quick glance to either shoreline along our three day trip down the river between Bluff and Mexican Hat on the San Juan provided first hand views of this overpowering plant species.  Only upon researching the topic did the controversial, complicated, conservation issues facing the West regarding this plant surface.  We gained a new appreciation for the longterm consequences of invasive species- a global issue of concern. 

Citations

1.)   http://www.tamariskcoalition.org/tamariskcoalition/index.html

2.)   http://www.discovermoab.com/tamarisk.htm

3)   https://www.hcn.org/issues/131/4174

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Ammonite Fossil Next To Quarter For Scale

Rafting down the upper section of the San Juan River from Sand Island to Mexican Hat, in southeastern Utah, there is a fossil stop near the entrance of Lime Creek, after the river emerges from the canyon. While much of the San Juan River passes through colorful layers of sandstone, the fossils of note are in a dark gray limestone.  Here is definite evidence that what is now desert was once covered by marine water.  The ancient Paradox Sea inundated a large area in the region and teemed with the marine life whose remains are before us.

I’m not the only one with “paleo-passion” (a term possibly coined by writer Donovan Webster in his article, “The Dino Wars: Who Owns American’s Fossils”, Smithsonian Magazine, April 2009, p. 48-57), but as an earth science educator, I feel protective of even one small trace of a fossil- what’s called a “fossil mold”, an impression made in the substrate. This is the only ammonite fossil I’ve seen in its actual place of formation and so to me it is noteworthy.  A thoughtless individual could damage the find, chiseling the mold out of the surrounding matrix, although I can’t imagine the tools or techniques that would be required to do so. It’s possible the true fossil form- the actual body of the animal making the mold- was removed by an eariler collector.  In discussing our itinerary on the river, I make sure our guide, Brett LeCompte, working for the Four Corners Outdoor School, stops at the fossil site.

We read and hear so much on our geo-cultural travel study trip to the Colorado Plateau about policies and practices regarding how to respectfully visit Ancestral Puebloan ruins, that I am curious about laws protecting fossils.  With a little research, I learn that currently fossils can be taken from private lands with permission of the owner for private collections or auction.  Some fossil materials, like petrified wood, in limited quantities, may be taken from public lands without permits.  However, additional legislation- the Paleontological Resources Protection Act- has been drafted mandating, “only trained, federally certified professionals be allowed to extract fossils from public lands,” (Webster, p. 56). The intent of the bill is to substanially increase penalties for illegal fossil excavation.

I wonder how much concern there is for ammonities which can be found for sell in fossil stores and on the web.  Webster logged onto Ebay and found an ammonite specimen, expecting to go for $3000. Excavating specimens from their resting place eliminates the educational and scientific context, and for me the special significance and value of the fossil.

Ammonite structure

This particular fossil, resulting from ages of compression and cementation, is an invertebrate specimen, a highly developed marine mollusk belonging to the extinct family of ammonites of the cephalopod class. Similar to the shells of snails, cephalapods shells are divided into chambers. Modern members of cephalopods, like the squid and octopus have only two gills, while members of the ammonoid and nautiloid families have four gills. (I can’t imagine gills being distinguishable in a fossil.)

These living animals first appeared during the Silurian Period, approximately 400 million years ago and were abundant and widespread in oceans during the Jurassic and Cretaceous geologic periods. Ammonites are important index fossils, because they can be used to provide a relative date for the rock layer in which they are found as species evolved over time.

The shells of ammonites had hollow chambers separated by walls called septa. A tube called the siphuncle, connected the body with the chambers allowing the animal to use water or air to change its buoyancy in order to rise or drop in the ocean.  Only the last and largest chamber was occupied by the living animal.  Ammonites vary greatly in size, the largest early forms could be 15 feet. Shell shapes varied as well; some can be snail like and others are uncoiled.

Ammonites fed on plankton and lived exclusively in marine environments and so their presence indicate the location of prehistoric seas.  Now, the arid West means little vegetation covers the rocks, making fossils like ammonites easier to find. The limestone and other sedimentary layers of rock deposited in ancient environments are now being exposed, revealing what this corner of the world was once like. For me, this fossil stop is as rich a window into the past as any of the human related historical sites we visit.

Rowing through the Paradox Formation

Travelling along this river by boat, takes you back in time, not only to the time of Ancestral Puebloans, but to a period where the environment was very different.  In relation, our modern concerns about how climate change might impact a particular region, seem so anthropomorphically insignificant.

A nice animated image show several perspectives of an ammonite can be found at:  http://www.paleodirect.com/ammonites.htm, accessed on 3-27-09.

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It wasn’t until we decided to hike the Devil’s Garden Trail in Arches National Park at the end of the trip, that I really became curious about the vulnerability of biological soil crusts- a new concept that surfaced in our trip out West- our river guides mentioned it. However, while in Arches, it’s hard to look at your feet and worry about conservation, when there are such spectacular, colorful vistas drawing the eyes upward. It was only on returning home that I finally had time to investigate biological soil crusts in more depth. Fortunately, the Visitor Guide to Arches National Park included an informative article which was a starting point for my research on the topic.

I was particularly intrigued about the collection of constituents making up the cryptobiotic soil- cyanobacteria, mosses, soil lichens, green algae, microfungi and bacteria (Arches National Park Visitor Guide, Vol.1, No.8, 205, Canyonlands Natural History Association, www.cnha.org, pg 6). Soil crust is estimated to cover almost 75 percent of the Colorado Plateau and is considered to be alive and ecologically important. Cyanobacteria is considered to be the most prevalent and important constituent. “When filaments of cyanobacteria are moistened, they advance through the soil, leaving sheaths of sticky mucilage on their trail. These gluey filaments bind to soil particles and, over time, can create an erosion-resistant surface,” (Arches National Park Visitor Guide, Vol.1, No.8, 205, Canyonlands Natural History Association, www.cnha.org, pg 6). This description of cyanobacteria reminded me of slugs leaving a trail of slime. I was intrigued to learn more about this aspect of biology; cyanobacteria had not been part of my earth science education. An inquiring mind requires interdisciplinary research.

Cyanobacteria are microscopic, photosynthesizing organisms, rich in chemical diversity, and some forms were once classified as blue green algae. Motile species have some microbiologists referring to them as “gliding bacteria” for their peculiar locomotion habits. Photosynthetic pigments can impart a host of different colors-yellow, red, violet, green, deep blue and blue-green… Cyanobacteria may be single-celled or colonial and are among the easiest microfossils to recognize, being larger than other bacteria. Some have remained the same for billions of years. Cyanobacteria also have the useful trait of being able to capture nitrogen from the air and can then convert it to a form plants can use. So, cyanobacteria serve as a fertilizer in this way- a useful trait in an ecosystem notoriously poor in nitrogen. The sticky sheaths described above also bind to calcium, potassium, and manganese making these nutrients available to plants in a useable form. “When wet, the sheaths will expand to ten times their dry size, enabling the soil crust to retain more moisture.” So, biological crusts provide stable soil, nutrients, and moisture. The term biological soil crust, also called cryptobiotic crust, emphasizes that these areas are “formed by living organisms and their by-products, creating a crust of soil particles bound together by organic materials” (soilcrust.org).

Back to trekking in the high desert in Arches National Park, when wayward foot steps trod upon the sheaths, they can be destroyed and the cyanobacteria as part of a delicate microsystem cease to function. So, the once “biological” crust is no longer fulfilling its vital roles. Pieces break off and are blown away by the wind. Loose sand covers the remaining biological crust blocking sunlight and photosynthesis stops. It is really important to stay on marked trails, walk on solid rock, or in drainages so as not to impact the biological crusts. The motto while in Arches is don’t “bust the crust”. Reminding hikers to leave no trace while exploring the Colorado Plateau takes on a special meaning and requires a new kind of vigilance in watching where one walks.

For most of us New Englanders, biological soil crusts are a novelty as they are a feature of arid environments. The closest connection we can make is with fragile, above timberline, alpine terrains that harbor rare plants- one of the reasons that the White Mountain National Forest doesn’t allow geo-caching in it’s boundaries.

I have seen media headlines, “Are We Loving Our Parks to Death?” I wondered if raising awareness about biological soil crusts figured into any VERP studies. VERP which stands for Visitor Experience and Resource Protection is a new focus for our public parks. Arches National Park has been part of a VERP study, in the last few years, which looks at visitor impacts as well as visitor perceptions; asking visitors what number of people seen on the trail is an “acceptable numberâ€? before they begin to feel crowded. They are shown computer-generated photos of the trail, each with an increasing number of people on them. The results help park managers make decisions. Reading about VERP reminded me of a new policy I’d heard about being instituted in the White Mountain National Forest; group sizes larger than 10 are discouraged from hiking trails, to help maintain a quality experience for all. Were certain visitor policies being universally shared across our public lands? How much attention was being paid to biological soil crusts. I did discover Soilcrust.org, a website dedicated to the topic.

I lived in Arizona from 1983-1987 and had never heard of biological soil crusts. So, I wondered when the term was coined, who did the research, and how it was conducted. Could I find and line up a scientist at Arches or in the area who could inform my next group of students to the region about this important concept. I personally wanted a closer glimpse into the world of cryptosoils so I could become a more informed, passionate advocate for protecting these fragile systems.

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I made an interesting observation on the part of the Navajo reservation I visited that you can always tell where the schools are, and therefore the middle of a town, by looking for the water towers. Water in this area has to be trucked in and stored in water towers. This water is strictly protected and rightly so. There are signs all over the school and surrounding area, warning against taking water off the school grounds, and the punishments for doing so. One of the areas I was in, Chinlee, Az, was fortunate enough to have a reservoir as well. However, this reservoir was tiny and the sediment was so thick that you could not see through it. It is common practice to have to filter the water that comes out of a tap and then boil that water to make it safe to use for people. Most people tend to buy bottled water and use that instead of the tap water for cooking and drinking water.

Another striking aspect on the reservation is the lack of plants. Because of the lack of water, no one has lawns or gardens. The only trees and bushes in the area are ones very well adapted to arid conditions and even these are located close to the only sources of water. Here in New England, we take for granted the fact that we are surrounded by greenery. Even if people don’t have lawns, there is lots of other vegetation on their property. This is not the case with Navajo land. Their “lawns” consist of dirt. There are sometimes a few plants that we would consider weeds, here and there, but mainly just dirt. They cannot afford the luxury of wasting water to keep up gardens or even just grass. This was depressing to myself and the other student I was with, but it is not to the Navajo people. Just as we are used to our green surroundings, they are used to the land on which they live. There is some good news though. Arizona is trying to figure out water conservation issues. The Arizona Department of Water Resources plays a big role by enforcing water codes and laws and putting together education and outreach programs. More can be learned about this by visiting their website at http://www.azwater.gov/dwr/default.htm. In addition to this department there are many other organizations such as the AMWUA at http://www.amwua.org/, the Water CASA at http://www.watercasa.org/, SAHRA http://www.sahra.arizona.edu/programs/water_cons//water_cons/, and many more. As long as there are people that care, there will always be hope to overcome the issue of water shortage.

– Alyssa Langley

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The PSU students will be assisting with a book project, entitled, ‘Discovering our Watershed: Voices and Images from students on the Colorado Plateau.’ If you’re a student in grades K-8 living on the Colorado Plateau you are eligible to submit an entry, by May 1st, 2006. Entries can be poetry, artwork, interviews, or essays about the Colorado River Watershed on the Colorado Plateau.

If you decide to follow our journey, a bonus feature is that a PSU librarian will be assisting us in answering questions that arise as we explore the region.

–Mary Ann McGarry, instructor

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