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Documents Flashcards Grammar checker. Charlet Abstract—Semi-arid shrublands and woodlands of Nevada are changing in the face of many daunting challenges. I compare Nevada to Iran to understand these challenges better, because Iran and Nevada have similar coloshate, geology, physiography, and latitude. Yet, Iran is different in its long history of civilization and concomitant human exploitation of the landscape.

Thus, we can look to Iran to gain insight into possible outcomes of our management actions in our remaining wild shrublands. The structure of Iranian vegetation is simple compared to that of Nevada.

Cklostate usually possesses only a single canopy layer and has low shrub species diversity, producing one-dimensional vegetation of low value for wildlife.

Shah-Kan-Daw: Anthropogenic Simplification of Semi-arid Vegetation Structure David A. Charlet

Docd Iranian flora shows the mark of long-term grazing and fire disturbance. In spite of enormous mountains, woodlands and montane forests are virtually non-existent. However, if we cllostate the processes that simplify vegetation to gain momentum, then we can look to Iran to see vocs monotonic future. At this time, three nations appear boldly in our newspapers. Conversely, a lack of cfr_insect opportunity in Mexico and other Latin Cfrj countries has led to a steady and substantial inflow of undocumented immigrants across our southern border.

Prominent in the news is Iran. Coincidentally, each of these nations poses not only political challenges to the United States but also colostste elements of their floras threaten the ecosystems of our semi-arid West.

Alien species have invaded our shrublands and woodlands. These species are affecting fundamental changes in basic ecosystem processes. Wildfires burn everywhere with dramatically increasing frequency Whisenant The changes in the vegetation are reflected in the status of formerly abundant vertebrates, and so the public learns from the news the threats to sage grouse in Artemisia shrublands and the desert tortoise in Larrea shrublands.

Misinformation abounds; we read in scientific literature that native juniper trees are invasive Ansley and Rasmussenpinyons are often regarded as such, and both are treated as if they were undocumented immigrants. A bright young Ph.

His concern was desertification in China. He was interested in shrubs and trees from Nevada that could hold back expanding sand dunes and so conserve the soil and the productivity of the land. I suggested he try species native to China, such as Tamarix. I am used to shrublands in my deserts and woodlands and forests in my mountains, with sand dunes and spring-fed wetlands as occasional fascinating features of a landscape already rich in species.

It is no wonder that we had difficulty understanding one another, as definitions of deserts vary greatly. For instance, McGinnies and others report that definitions of deserts based on precipitation alone vary from a maximum mean annual precipitation of 5 cm to as much as 38 cm!

Whatever we call them, in much of China—and as I was soon to find out in Iran as well—basic ecosystem processes in semi-arid regions are failing. By comparison, in Nevada, these processes are merely docw. Such a collapse inevitably leaves a burdensome colsotate wake, and potentially leads to tragic human consequences Diamond Humans deliver a one-two punch to wild ecosystems: Human activities in Nevada during the last years have caused countless disturbances.

Shah-Kan-Daw: Anthropogenic Simplification of Semi-arid Vegetation Structure David A. Charlet

They have accelerated the spread of alien weeds, such as cheatgrass Bromus tectorum5 Charlet Shah-Kan-Daw: Anthropogenic Simplification of Semi-arid Vegetation Structure that may lead to their dominance throughout much of the region Billings ; Bradley and Mustard ; Knapp Groundwater pumping constitutes a major threat to valley bottom phreatophytic vegetation and unique spring ecosystems Charlet Utility corridors cut large swaths throughout the state, fragmenting formerly continuous ecosystems, creating convenient migration corridors, and providing suitable ground for the establishment of these invasive species Bradley and Mustard ; Lathrop and Archbold In Nevada, alien species are notoriously flammable and invasive.

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Cheatgrass provides unbroken patches between shrubs, dries early in the growing season of most native plants, and so provides fine fuels early in the season that carry fires throughout large areas Young and Evans Once burned, the likelihood of another catastrophic fire returning is high, as fire return intervals are now shorter by as much as an order of magnitude from what they were before settlement Whisenant Life history characteristics conspire to accelerate the ascendancy of these species, which can prevent the establishment of shrubs even in the absence of returning fires Billings The prospect of increasing atmospheric CO2 levels almost ensures that this and other opportunistic aliens such as Bromus madritensis Smith and others will come to dominate the region.

The net effect of alien brome grasses in Nevada is to impoverish biodiversity Billings by converting shrublands and semi-arid woodlands to annual grasslands Bradley and others Moreover, the consequences of grassland replacement of shrublands and woodlands in the global carbon budget are that Nevada semi-arid vegetation rapidly transforms from a carbon sink to a carbon source Bradley and others Twenty years ago, Young and Sparks made an ominous, and hopefully not prophetic, prediction about the sagebrush shrublands of the Great Basin: The way is thus paved for repeated burnings and a continuing downward spiral of degradation.

Over the 35 years I have lived in Nevada, spending much of that time in its wild mountains and basins, I have witnessed a continuing and expanding degradation of its vegetation formations.

I was troubled by these changes, and wanted to get closer to the source of these problems. So, when an opportunity presented itself for me to go to Iran, I pursued it with enthusiasm and diligence. While they may have arrived here via Europe, most of the invasive species that are destabilizing Nevada ecosystems are native to Iran or elsewhere in the Middle East. Cheatgrass Bromus tectorum is aggressively invading upland shrublands and semi-arid woodland formations. Although not spreading as rapidly, saltlove Halogeton glomeratus continues to expand in the colostahe zone; occasionally forming pure stands over large areas.

Russian-olive Elaeagnus angustifolium is mainly a problem in riparian areas in central Nevada, but salt-cedar Tamarix ramosissima is rapidly gaining the upper hand along streams and at springs throughout Nevada. It makes sense to see the landscapes 6 from where these alien elements are native, in order that colosyate may better understand the threats to our region. Latitude, physiography, and climate are shared by Iran and Nevada.

Because copostate its size, Iran occupies a wider latitudinal range than Nevada, but virtually all of Nevada lies within the latitudinal range of Iran. A considerable amount of Iranian territory occupies coastal regions along the Persian Gulf, Indian Ocean, and Caspian Sea, environments that have no equivalent in Nevada.

Nevertheless, the great interior of Iran is much larger than the Great Basin and Mojave cloostate, about copostate of which is in Nevada.

Iran is a land of large, parallel mountain ranges with large intermountain, internally drained basins Zohary While the western boundary of the Basin and Range province drains to the Pacific Ocean, the western slopes of the Zagros Mountains of western Iran drain into cfei Persian Gulf.

The northern boundary of the Great Basin drains into the Columbia River and thence to the Pacific, much as the northern slopes of the Alborz Mountains of Iran drain into the Caspian Sea. The Alborz Mountains are large, equivalent cfro length and breadth to the Sierra Nevada both are km longbut considerably higher than the Sierra Nevada and the Zagros Mountains.

Although not taller than the Alborz Mountains, the Zagros Mountains are more massive, spanning 1, km in length and km in width. Mount Dena is the highest point in the Zagros Mountains at 5, m 16, ftcompared to the highest point in the Sierra Nevada, Mount Whitney 4, m; 14, ft. Iran has four clusters of small glaciers: The non-coastal climates of Iran and Nevada are remarkably similar.

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Both have interior climates in the rain-shadow of enormous mountain ranges that intercept storms coming ashore and strip them of their moisture. Anthropogenic Simplification of Semi-arid Vegetation Structure by mainly winter precipitation and have cold winters in the north and hot summers in the south.

For cfri_inxect, the northern Nevada city of Reno occurs at the base of the Sierra Nevada, much like Tehran sits at the base of the Alborz Mountains. Las Vegas and Esfahan are southern cities in hot deserts amidst treeless, arid mountains. Paradise Valley and Urumieh are both high agricultural valleys situated between moderately sized mountains that develop Charlet large snow packs. Both cities occur near high mountains and at moderately high elevations, with Virginia City at about m A.

L while Tabriz is situated at m A. In each case, not only are average annual temperature and precipitation close table 1but the monthly distribution of precipitation and temperature is also dofs fig.

Figure 1—Iran, its cfri_inzect nations, and geographic features named in the text. The Alborz Mountains extend across northern Iran from Turkey to Afghanistan, connecting the mountains of eastern Europe with the mountains of Central Asia.

The Zagros Mountains run nearly the entire north-south dimension of Iran along its western border. Iran data from the Iran Meteorological Organization Nevada data from the Western Regional Climate Center L [18, ft] in the Alborz Mountains. Two vast interior basins in Iran, the Coolostate and the Dasht-e-Lut are reminiscent of the Bonneville Basin of Utah, although far larger than Bonneville and not as dissected by mountain ranges as is the Lahontan Basin of Nevada, nor do they possess permanent lakes.

However, Lake Urumieh in northwestern Iran, situated between the Alborz and Zagros Mountains, is very similar to the Great Salt Lake colosate the lakes even possess at the base of their food webs closely related brine shrimp Artemia urmiana in Charlet Urumieh and Artemia franciscana in the Great Salt Lake D. Christopher Rogers, written communication Today both Iran and Nevada are experiencing dramatic human population growth fig.

And so at this time in both places, demands on water, minerals, and other natural resources, including the land itself, are escalating at an ever-increasing pace. The main difference between the two regions is that in Iran during the Holocene, the vegetation evolved in a context of agriculture, pastoralism, metallurgy, and denser human populations. Therefore, an investigation of the flora and vegetation of Iran should provide insights on management and conservation of the Great Basin and Mojave Desert of Nevada.

Figure 3—Human population growth in Nevada top and Iran bottomto Both experienced geometric population increases during the 20th century. The rate of growth slowed in Iran during — due to the IranIraq war. Instead, these monotonic shrublands extend across vast areas of the Turan Biosphere Preserve and vegetated portions of the Dasht-e-Kavir Moore and Bhadresa Widely spaced chenopodiaceous shrubs, in genera such as Atriplex, Suaeda, and Haloxylon, dominate salt deserts in terminal basins.

Upland xeric vegetation is largely dominated by short Artemisia shrublands, again with few other shrub species. Shrublands are omnipresent in the montane zone; these dominated largely by thorny members of the fabaceous genera Astragalus and Onobrychis. Similarly, subalpine habitats do not have multi-story, highly diverse shrublands. Instead, these are invariably dominated by a single low, shrubby Astragalus species.

Inter-shrub spaces are dominated by a wide array of geophytes largely in the genera Lilium, Allium, and Tulipa whether in the subalpine, the montane, or the low deserts. Desert shrublands sometimes have grasses such as Stipa barbata, while montane shrublands are sometimes accompanied by bunchgrasses such as Agropyron spp.

While the landscapes before me were familiar, they also were eerie in what was absent. Where are the forests? Why is neither Pinus nor Picea even on my list?